Implantable medical device delivery system and method

Abstract

A delivery system and method are described that include a catheter (102) and a stylet (200). The catheter (102) defines a delivery lumen (146) therethrough. The stylet (200) extends through the delivery lumen (146) of the catheter (102) and is movable relative to the catheter (102). The stylet (200) includes a tip section (220) at a distal end (212) of the stylet (200). The tip section (220) selectively transitions between a narrow state and a flared state. The tip section (220) in the flared state has a greater lateral extension than the tip section (220) in the narrow state. The tip section (220) in the narrow state is configured to project beyond a distal end (116) of the catheter (102) to pierce cardiac tissue. The tip section (220) is configured to transition from the narrow state to the flared state to anchor the stylet (200) to the cardiac tissue.

Description

IMPLANTABLE MEDICAL DEVICE DELIVERYSYSTEM AND METHODCROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority to U.S. Provisional Application No. 63 / 708,062 (filed 16-October-2024), the entire disclosure of which is incorporated herein by reference.BACKGROUND

[0002] Embodiments of the present disclosure relate generally to systems and methods for implanting medical devices (IMDs) within a patient, such as delivery systems for implanting IMDs or leads thereof into cardiac tissue of the patient.

[0003] Some IMDs function to monitor cardiac activity of a patient, provide electrotherapy to the cardiac tissue, and / or the like. Some cardiac pacemakers and implantable cardioverter-defibrillators (ICD) use insulated wires called leads to monitor the heart and provide stimulation therapy by delivering electrical pacing pulses and / or shocks. Some leads pierce the myocardial tissue of the heart to deliver stimulation therapy directly into the tissue. Leadless pacemakers can monitor the heart and deliver stimulation therapy without the use of leads. References herein to IMDs encompass both leads of IMDs and leadless IMDs, unless specified.

[0004] The implant procedure of these IMDs can involve catheters that transport the IMD through an access introducer into the subject. The catheter may navigate the venous system and / or cardiac anatomy to position the IMD at a target anatomical location. The IMD may be transported within a lumen of the catheter. A thin structural member called a stylet may be used to assist the implant procedure by enhancing the structural stiffness of the catheter and / or providing a means of steering the catheter through the patient anatomy. The implant procedure may fixate (e.g., secure) a distal end of the IMD to the cardiac tissue at15870W0011 (013-0619PCT) 1 PATENTthe target location. The IMD may provide stimulation therapy when fixated to the cardiac tissue. Upon placement of the IMD at the target anatomical location, the catheter and stylet are withdrawn from the subject while the IMD remains.

[0005] The heart is complex and electrical conduction through the cardiac tissue varies based on location. It is difficult to determine if a current implant location of the IMD is better than another location at conducting electrical energy. The implant procedure may be an iterative process to discover an implant location for the IMD along the heart that provides better pacing characteristics (e.g., better electrical conduction) than other potential implant sites along the heart. The iterative process to implant the lead can be an invasive one due to the exploratory piercings of the cardiac tissue by the lead. A system is desired to reduce the invasiveness of the cardiac tissue when investigating candidate implant sites.

[0006] Furthermore, even after the implant site for an IMD is determined, it may be difficult to reliably and accurately deliver the IMD to the target implant site. For example, the catheter may move relative to the heart, causing the IMD held by the catheter to deviate from a desired position and miss the target implant site. A system is also desired to reliably and accurately deliver the IMD (e.g., lead) to a target implant site within the cardiac tissue.SUMMARY

[0007] In accordance with embodiments herein, a delivery system is provided that includes a catheter and a stylet. The catheter defines a delivery lumen therethrough. The stylet is configured to extend through the delivery lumen of the catheter and is movable relative to the catheter. The stylet includes a tip section at a distal end of the stylet. The tip section is configured to selectively transition between a narrow state and a flared state. The tip section in the flared state has a greater lateral extension than the tip section in the narrow state. The tip section in the narrow state is configured to project beyond a distal end of the15870W0011 (013-0619PCT) 2 PATENTcatheter to pierce cardiac tissue, and the tip section is configured to transition from the narrow state to the flared state to anchor the stylet to the cardiac tissue.

[0008] In an example, the delivery system includes a lead of an implantable medical device (IMD). The lead may include a lead body that defines a lead lumen therethrough. The stylet may extend through the lead lumen of the lead and may be movable relative to the lead. The lead may extend through the delivery lumen of the catheter and may be movable relative to the catheter. While the stylet is anchored to the cardiac tissue via the tip section in the flared state, the lead may be advanced relative to the catheter along a length of the stylet so that a distal end of the lead penetrates the cardiac tissue and follows a path defined by the stylet through the cardiac tissue.

[0009] In an example, the stylet may include an electrode located on the tip section or proximate to the tip section. The electrode on the stylet may define a bipolar electrode pair with a second electrode that is disposed on one of the catheter or an IMD that is held by the catheter. The bipolar electrode pair may deliver stimulation energy to the cardiac tissue and / or sense evoked responses from the cardiac tissue to evaluate a site of interest along the cardiac tissue.

[0010] The stylet may include a core element and an outer sheath that surrounds and contains the core element in the narrow state of the tip section. The outer sheath may be retractable relative to the distal end of the stylet to expose the core element and permit the tip section to transition to the flared state. The core element may be biased to automatically laterally project beyond the outer sheath, achieving the flared state, in response to retraction of the outer sheath to expose the core element. The core element may include a shape memory material. The core element may automatically assume a coiled shape in the flared state. In another example, the core element may include multiple prongs that are biased to spread apart in different directions when transitioning from the narrow state to the flared state. In another example, the stylet includes a balloon at the tip15870W0011 (013-0619PCT) 3 PATENTsection. The balloon may be inflated to transition the tip section from the narrow state to the flared state.

[0011] The delivery lumen of the catheter may be a first delivery lumen, and the catheter may define a second delivery lumen laterally spaced apart from the first delivery lumen. The second delivery lumen may have a greater cross- sectional size than the first delivery lumen. The second delivery lumen may receive at least a portion of an IMD that is movable through the second delivery lumen relative to the catheter.

[0012] In accordance with embodiments herein, a method for delivering an IMD to patient cardiac tissue is provided. The method includes loading a catheter into a patient towards cardiac tissue at a site of interest (SOI). The catheter defines a delivery lumen therethrough. The method includes advancing a stylet through the delivery lumen of the catheter so that a distal end of the stylet projects beyond a distal end of the catheter and pierces the cardiac tissue at the SOI. The stylet includes a tip section at the distal end that is configured to selectively transition between a narrow state and a flared state. The tip section in the flared state has a greater lateral extension than the tip section in the narrow state. The tip section is in the narrow state when advancing through the delivery lumen and piercing the cardiac tissue. The method includes transitioning the tip section to the flared state to anchor the stylet to the cardiac tissue.

[0013] In an example, the stylet extends through a lead lumen of a lead of an IMD and is movable relative to the lead. The lead extends through the delivery lumen of the catheter and is movable relative to the catheter. The method may include advancing the lead relative to the catheter along a length of the stylet, while the stylet is anchored to the cardiac tissue, so that a distal end of the lead penetrates the cardiac tissue and follows a path defined by the stylet through the cardiac tissue. In an example, the method includes transitioning the tip section of the stylet to the narrow state after advancing the lead into the cardiac tissue. The method may include withdrawing the stylet in the narrow state from the cardiac15870W0011 (013-0619PCT) 4 PATENTtissue through the lead lumen of the lead while the distal end of the lead remains in the cardiac tissue.

[0014] Advancing the stylet to pierce the cardiac tissue at the SOI may include advancing the distal end of the stylet through a thickness of a septal wall so that the distal end enters a chamber. Transitioning the tip section to the flared state may include transitioning the tip section to the flared state within the chamber so that the tip section in the flared state is configured to abut against a back side of the septal wall.

[0015] In an example, the stylet includes a core element and an outer sheath that surrounds and contains the core element in the narrow state of the tip section. Transitioning the tip section to the flared state may include retracting the outer sheath relative to the distal end of the stylet to expose the core element and permit the tip section to transition to the flared state. In another example, the stylet includes a balloon at the tip section. Transitioning the tip section to the flared state may include inflating the balloon.

[0016] In accordance with embodiments herein, a delivery system is provided that includes a lead of an implantable medical device (IMD) and a stylet. The lead includes a lead body that defines a lead lumen therethrough. The stylet is configured to extend through the lead lumen of the lead and is movable relative to the lead. The stylet includes a tip section at a distal end of the stylet. The tip section is configured to selectively transition between a narrow state and a flared state. The tip section in the flared state has a greater lateral extension than the tip section in the narrow state. The tip section in the narrow state is configured to project beyond a distal end of the lead to pierce cardiac tissue of a heart at a site of interest (SOI). The tip section is configured to transition from the narrow state to the flared state while the tip section is within the heart to anchor the stylet to the heart. The lead is configured to be advanced into the cardiac tissue while the stylet is anchored to the heart so that the lead follows a path defined by the stylet through the cardiac tissue.15870W0011 (013-0619PCT) 5 PATENT

[0017] In an example, the stylet includes a core element and an outer sheath that surrounds and contains the core element in the narrow state of the tip section. The outer sheath may be retractable relative to the distal end of the stylet to expose the core element. The core element may be biased to automatically laterally project beyond the outer sheath, achieving the flared state, in response to retraction of the outer sheath to expose the core element.

[0018] In an example, the delivery system includes a catheter defining a delivery lumen therethrough. The lead may extend through the delivery lumen of the catheter and may be movable relative to the catheter. The tip section of the stylet in the narrow state may project beyond the distal end of the lead and a distal end of the catheter to pierce the cardiac tissue at the SOI.

[0019] The stylet may include an electrode located on the tip section or proximate to the tip section. The electrode may define a bipolar electrode pair with a second electrode that is disposed on the lead or a catheter that holds the lead. The bipolar electrode pair may deliver stimulation energy to the cardiac tissue and / or sense evoked responses from the cardiac tissue to evaluate the SOI.BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 illustrates a schematic cutaway view of a heart relative to an IMD.

[0021] Figure 2 is another schematic cutaway view of the heart showing a location of the bundle of His (e.g., His bundle) in the heart.

[0022] Figure 3 illustrates a delivery system formed in accordance with an embodiment.

[0023] Figure 4 illustrates a distal end segment of the delivery system according to an embodiment.15870W0011 (013-0619PCT) 6 PATENT

[0024] Figure 5 illustrates the distal end segment of the delivery system with a lead projecting beyond a catheter and a stylet projecting beyond the lead.

[0025] Figure 6 is a cross-sectional view of a tip section of the stylet according to at least one embodiment.

[0026] Figure 7 illustrates the tip section of the stylet in a flared state according to a first example embodiment of the core element.

[0027] Figure 8 shows the lead and the stylet at a first stage in an implant procedure according to an embodiment.

[0028] Figure 9 shows the lead and the stylet at a second stage in the implant procedure.

[0029] Figure 10 shows the lead and the stylet at a third stage in the implant procedure.

[0030] Figure 11 shows the lead and the stylet at a fourth stage in the implant procedure.

[0031] Figure 12 illustrates the stylet projecting from the lead according to a second embodiment of the stylet.

[0032] Figure 13 is an enlarged view of the tip section of the stylet shown in Figure 12.

[0033] Figure 14 illustrates the stylet of the delivery system according to a third embodiment showing the tip section in the narrow state.

[0034] Figure 15 illustrates the stylet of Figure 14 showing the tip section in the flared state.

[0035] Figure 16 illustrates the distal end segment of the delivery system according to a second embodiment of the catheter.15870W0011 (013-0619PCT) 7 PATENT

[0036] Figure 17 is a flow chart of a method 400 of implanting a lead or an IMD within cardiac tissue of a patient according to an embodiment.

[0037] Figure 18 illustrates a block diagram of an exemplary IMD that is configured to be implanted into a patient in accordance with one or more embodiments herein.DETAILED DESCRIPTION

[0038] It will be readily understood that the components of the embodiments as generally described and illustrated in the figures herein, may be arranged and designed in a wide variety of different configurations in addition to the described example embodiments. Thus, the following more detailed description of the example embodiments, as represented in the figures, is not intended to limit the scope of the embodiments, as claimed, but is merely representative of example embodiments.

[0039] Reference throughout this specification to “one embodiment” or “an embodiment” (or the like) means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment. Thus, appearances of the phrases “in one embodiment” or “in an embodiment” or the like in various places throughout this specification are not necessarily all referring to the same embodiment.

[0040] Furthermore, the described features, structures, or characteristics may be combined in any suitable manner in one or more embodiments. In the following description, numerous specific details are provided to give a thorough understanding of embodiments. One skilled in the relevant art will recognize, however, that the various embodiments can be practiced without one or more of the specific details, or with other methods, components, materials, etc. In other instances, well-known structures, materials, or operations are not shown or described in detail to avoid obfuscation. The following description is intended only by way of example, and simply illustrates certain example embodiments.15870W0011 (013-0619PCT) 8 PATENT

[0041] The methods described herein may employ structures or aspects of various embodiments (e.g., systems and / or methods) discussed herein. In various embodiments, certain operations may be omitted or added, certain operations may be combined, certain operations may be performed simultaneously, certain operations may be performed concurrently, certain operations may be split into multiple operations, certain operations may be performed in a different order, or certain operations or series of operations may be re-performed in an iterative fashion. It should be noted that, other methods may be used, in accordance with an embodiment herein. Further, wherein indicated, the methods may be fully or partially implemented by one or more processors of one or more devices or systems. While the operations of some methods may be described as performed by the processor(s) of one device, additionally, some or all of such operations may be performed by the processor(s) of another device described herein.

[0042] Embodiments may be implemented in connection with one or more implantable medical devices (IMDs). Non-limiting examples of IMDs include neurostimulator devices, implantable leadless monitoring and / or therapy devices, catheters, and / or alternative implantable medical devices. For example, the IMD may represent a cardiac monitoring device, pacemaker, cardioverter, cardiac rhythm management device, defibrillator, neurostimulator, leadless monitoring device, leadless pacemaker and the like. For example, the IMD may include one or more structural and / or functional aspects of the device(s) described in U.S. Patent 9,333,351 “Neurostimulation Method And System To Treat Apnea” and U.S. Patent 9,044,610 “System And Methods For Providing A Distributed Virtual Stimulation Cathode For Use With An Implantable Neurostimulation System”, which are hereby incorporated by reference.

[0043] All references, including publications, patent applications and patents, cited herein are hereby incorporated by reference to the same extent as if each reference were individually and specifically indicated to be incorporated by reference and were set forth in its entirety herein.15870W0011 (013-0619PCT) 9 PATENT

[0044] Embodiments set forth herein include delivery systems for implanting IMDs and methods for using the delivery systems to implant IMDs. Particular embodiments of the delivery system include a stylet that has an expandable distal tip for selectively anchoring the stylet to cardiac tissue of a patient’s heart. The stylet is delivered to the heart within a lumen of a delivery catheter or a lead of an IMD. In an example, the stylet is disposed within a lead lumen of a lead, which itself is disposed within a delivery lumen of a catheter. The distal tip of the stylet may be in a narrow state when contained within the lumen. The stylet may remain in the narrow state when advanced beyond a distal end of the catheter and / or the lead to pierce the cardiac tissue. The distal tip may be selectively expanded from the narrow state to a flared state when extending into the heart to secure the delivery system to the heart. For example, the flared distal tip provides a fixation mechanism for securing the delivery system in place relative to the cardiac tissue. In an example application, the stylet is used to secure the delivery system to a septal wall of the heart to assist with implanting the IMD to the septal wall at a target implant site. For example, when the distal tip of the stylet is expanded, the stylet may resist forces that would otherwise laterally dislodge the delivery system (e.g., the catheter, lead, and / or stylet) and / or pull the delivery system away from the cardiac tissue. The septal wall in an example application may be a ventricular septal wall separating a left ventricular chamber from a right ventricular chamber.

[0045] In addition to anchoring the delivery system to the heart, the stylet may be used for additional beneficial functions, such as exploratory testing of different candidate implant sites for conduction system pacing (CSP) and guidance of the lead or IMD to a target implant site. For example, the stylet may be used as a guidewire that guides the IMD to the target implant site within the heart. The stylet may extend through a lumen of a cardiac lead of the IMD, so that the lead surrounds the stylet. The stylet may be advanced beyond a distal end of the lead to pierce the cardiac tissue. Once the stylet is embedded in the cardiac tissue and the distal tip is expanded to the flared state to secure the stylet in place, the lead may be advanced to pierce the cardiac tissue. The lead, still surrounding the stylet,15870W0011 (013-0619PCT) 10 PATENTfollows a path of the stylet through the cardiac tissue towards the target implant site. Once the lead reaches the target implant site, the stylet can be released from the cardiac tissue by transitioning the distal tip to the narrow state and then withdrawing the stylet through the lead lumen. The lead may remain fixed in place at the implant site as the stylet exits the cardiac tissue and is subsequently withdrawn through a proximal end of the lead.

[0046] The stylet in an example may assist a physician with selecting an implant site for the IMD within the cardiac tissue of the patient heart. The selected implant site may be a site for the IMD to provide pacing stimulation therapy. The stylet may be a thin, minimally-invasive wire (e.g., when in the narrow state), that is significantly thinner than a cardiac lead or leadless IMD. Iterative penetration of the distal end of the stylet into the cardiac tissue to investigate implant sites with desirable conductive properties for pacing is less invasive than using the lead or IMD for the same process. The stylet may have an electrode at or near the distal end of the stylet. The distal electrode may assist with testing various sites of interest (SOI) prior to fixating (e.g., securing) the IMD into the cardiac tissue. For example, the stylet may be implanted at different locations and different depths into the cardiac tissue to reach multiple SOI. At each SOI, the electrode of the stylet may be used to define part of a bipolar electrode pair for analyzing electrically conductive properties of the SOI. Data generated by the bipolar electrode pair can be used to select which SOI to designate at the target implant location of the IMD. As a result, the IMD can be delivered directly to the target implant location, without participating in the iterative site selection investigation.

[0047] The stylet of the delivery system may enable relatively quick and efficient investigation into different SOI to select which site is suitable as the target implant location for the IMD with limited or no trauma to the cardiac tissue because the stylet is very small and thin. For example, the delivery system may permit temporary bipolar pacing at each SOI without requiring the IMD to be implanted into the cardiac tissue. The IMD (e.g., the lead) may only be implanted into the15870W0011 (013-0619PCT) 11 PATENTcardiac tissue after selecting the target implant location based on the investigation. And, as described above, the stylet may further assist with the implantation of the IMD by securing the delivery system to the heart in the flared state and / or providing a path along which the lead is advanced towards the target implant location.

[0048] Figure 1 illustrates a schematic cutaway view of a heart 10 relative to an IMD 50. The heart 10 includes a right atrium RA, a right ventricle RV, a left atrium LA, and a left ventricle LV. During normal operation of the heart 10, deoxygenated blood from the body is returned to the right atrium RA from the superior vena cava 12 and inferior vena cava 14. The right atrium RA pumps the blood through the atrioventricular or tricuspid valve 16 to the right ventricle RV, which then pumps the blood through the pulmonary valve 18 and the pulmonary artery 20 to the lungs for reoxygenation and removal of carbon dioxide. The newly oxygenated blood from the lungs is transported to the left atrium LA, which pumps the blood through the mitral valve 22 to the left ventricle LV. The left ventricle LV pumps the blood through the aortic valve 24 and the aorta 26 throughout the body.

[0049] Figure 2 is another schematic cutaway view of the heart 10 showing a location of the bundle of His 30 (e.g., His bundle) in the heart. The His bundle 30 consists of fast-conducting muscle fibers that begin at the atrioventricular node in the right atrium and pass to the interventricular septum (e.g., septal wall) 32. The His bundle 30 divides in the interventricular septum into a right branch and a pair of left branches. The right branch travels along the right side of the interventricular septum and supplies excitation to the right ventricle. The pair of left branches travel along the left side of the interventricular septum 32 and supply excitation to the left ventricle. The fibers in the branches terminate in an extensive network of Purkinje fibers which distribute excitation pulses to the layer of cells beneath the endocardium. The His bundle 30 serves as an initial pathway for electrical impulses to travel from the atria to the ventricles. For example, the His bundle 30 transmits electrical signals from the AV node to the right and left bundle branches. The left bundle branch (LBB) is one of the two bundle branches of the His bundle15870W0011 (013-0619PCT) 12 PATENT30, traveling along the left side of the interventricular septum 32. The LBB carries electrical impulses to the left ventricle, facilitating synchronized contraction of the left ventricle.

[0050] Returning to Figure 1 , the IMD 50 includes a pulse generator 52 that is operably coupled to a lead 54 through a lead adaptor 56. The lead adaptor 56 is configured to receive a lead connector (not shown) of the lead 54. Although the IMD 50 includes only one lead in Figure 1 , the IMD 50 may include multiple leads in other embodiments. The lead 54 is a cardiac lead designed to penetrate the cardiac tissue of the heart 10. In an example, the lead 54 may be positioned and advanced to penetrate the endocardium in contact with His bundle 30 and / or the LBB. The lead 54 may enter the vascular system through one of several possible vascular access sites. For example, the lead 54 may extend through the superior vena cava 12 to the right atrium RA.

[0051] In Figure 1 , the IMD 50 is a cardiac pacemaker. In other embodiments, however, the IMD 50 may include an ICD, a CRT-D, an ICD coupled with a pacemaker, and the like. The IMD 50 may be a dual-chamber stimulation device capable of treating both fast and slow arrhythmias with stimulation therapy, including cardioversion, defibrillation, and pacing stimulation, as well as capable of detecting heart failure, evaluating its severity, tracking the progression thereof, and controlling the delivery of therapy and warnings in response thereto. The IMD 50 may be controlled to sense atrial and ventricular waveforms of interest, discriminate between two or more ventricular waveforms of interest, deliver stimulus pulses or shocks, and inhibit application of a stimulation pulse to a heart based on the discrimination between the waveforms of interest and the like. The IMD 50 may provide pacing stimulation to the His bundle 30 and / or the LBB, referred to as His bundle pacing (HBP) and left bundle branch pacing (LBBP), respectively.

[0052] Although not shown, the IMD 50 may wirelessly communicate with an external device. The external device may be used by a physician or other15870W0011 (013-0619PCT) 13 PATENTtechnician to select and / or modify therapy parameters to be implemented by the IMD 50.

[0053] Figure 3 illustrates a delivery system 100 formed in accordance with an embodiment. The delivery system 100 in the illustrated example includes a catheter (or introducer sheath) 102, a handle 104, a connector assembly 106, and a fluid flushing assembly 108. The delivery system 100 includes additional components not visible in Figure 3. For example, the delivery system 100 includes a stylet 200 (shown in Figure 4). The delivery system 100 may also include an IMD. In various examples, the IMD of the delivery system 100 is or includes a cardiac lead 202 (shown in Figure 4). The delivery system 100 may have at least some different components in other examples. The fluid flushing assembly 108 may be omitted in at least one example. The delivery system 100 may also include an obturator / dilator. A distal end of the obturator / dilator may be wedge-shaped or cone-shaped (e.g., conical). The obturator / dilator may be used to enlarge an opening (e.g., incision) in the patient for accessing the vascular system. The obturator / dilator may provide support for the catheter 102 as the catheter 102 is maneuvered through the vascular system of the patient.

[0054] The connector assembly 106 may include an electrical connector 110. In an example, the electrical connector 110 may be electrically connected to one or more electrodes of the delivery system. For example, the electrical connector 110 may be coupled to a proximal end of the stylet 200 and electrically connected to one or more electrodes of the stylet. The connector assembly 106 may selectively communicatively connect to a pacing system analyzer device 111. The pacing system analyzer device 111 , as explained herein, may use the delivery system 100 to electrically map multiple candidate sites of interest (SOI) along patient cardiac tissue to select a target implant location for long-term implant of an IMD. For example, the pacing system analyzer device 111 may include a pulse generator, a memory device, and processing circuitry. The processing circuitry may control the pulse generator to generate a pacing pulse that is delivered by15870W0011 (013-0619PCT) 14 PATENTone or more electrodes of the stylet 200 to myocardial tissue at a SOI. The processing circuitry may then analyze signals indicative of an evoked response in the myocardial tissue to the pacing pulse.

[0055] The handle 104 may include a hemostasis hub 112 for accepting and coupling to (e.g., tethering to) a proximal end 114 of the catheter 102. The catheter 102 extends from the proximal end 114 to a distal end 116 of the catheter 102. In an embodiment, the catheter 102 has at least one lumen that extends through the catheter 102 from the proximal end 114 to the distal end 116. Each lumen may be open at both ends 114, 116. The hemostasis hub 112 permits access to the lumen(s) of the catheter 102. The lumen(s) of the catheter 102 are referred to herein as delivery lumen(s) to distinguish from a lead lumen of the lead 202. The fluid flushing assembly 108 may mechanically couple to the hemostasis hub 112 and fluidly couple to the catheter delivery lumen through the hemostasis hub 112.

[0056] The catheter 102 is configured to introduce both the stylet 200 and the lead 202 of an IMD (or an entire IMD) into a designated anatomical region of a patient, such as the heart. For example, the stylet 200 and the lead 202 may be loaded into one or more lumens of the catheter 102. The catheter 102 may be steerable to navigate through a tortuous vascular system of the patient. The catheter 102 may be steered to position a distal end segment 124 of the delivery system 100 proximate to a SOI, with the distal end of the catheter 102 facing the cardiac tissue at the SOI. The catheter 102 may include a plurality of sheath segments or portions along its length, and at least some of the sheath segments may be bendable relative to other sheath segments. An operator may steer the catheter 102 by holding the handle 104 and manipulating at least one actuator 135 coupled to the handle 104. Based on its intended use, the catheter 102 may be designed to exhibit various properties. For example, the catheter 102 may be maneuverable and have a sufficient columnar strength for being inserted through the tortuous vascular system. The catheter 102 may also have sufficient kinkresistance so as to bend smoothly.15870W0011 (013-0619PCT) 15 PATENT

[0057] Figure 4 illustrates the distal end segment 124 of the delivery system 100 according to an embodiment. The catheter 102 includes a catheter body 140. The catheter body 140 may extend the length of the catheter 102 from the proximal end 114 of the catheter 102 to the distal end 116 of the catheter 102. The catheter body 140 extends lengthwise along a central axis 144 of the catheter body 140 from the proximal end 114 to the distal end 116. The central axis 144 may extend along a curved path that changes as the catheter 102 is flexed, bent, or otherwise manipulated. In an example, the catheter body 140 defines a single delivery lumen 146. The delivery lumen 146 extends lengthwise along the catheter body 140. The delivery lumen 146 may be parallel with the central axis 144. For example, the central axis 144 may extend through the delivery lumen 146. The delivery lumen 146 may be open at the distal end 116 of the catheter 102. For example, the catheter 102 may have an access opening 148 to the delivery lumen 146 at the distal end 116. The delivery lumen 146 may also be open at the proximal end 114 to receive a payload therein. The payload in an example is both the lead 202 and the stylet 200. In an example, the delivery lumen 146 is cylindrical, with a circular cross-sectional shape. In another example, the delivery lumen 146 may have an elliptical or oval shape. The dimension of the delivery lumen 146 in an example may be 4 French (F) to 9 F.

[0058] In the illustrated embodiment, the delivery lumen 146 is sized to receive the (cardiac) lead 202 of an IMD therein. The lead 202 is disposed within the delivery lumen 146 in Figure 4. The delivery lumen 146 is also sized to provide clearance to permit the lead 202 to move relative to the catheter 102. With the clearance, the lead 202 can be advanced and / or retracted relative to the catheter 102. For example, if the lead 202 has a diameter of 6 F, the delivery lumen 146 may have a cross-sectional dimension (e.g., diameter) of 7 F or 8 F. The clearance may reduce friction between the lead 202 and an inner surface of the catheter body 140 that defines the delivery lumen 146.15870W0011 (013-0619PCT) 16 PATENT

[0059] In an embodiment, the lead 202 defines a lumen 204, referred to herein as lead lumen 204. The lead lumen 204 may by defined by a lead body 206 of the lead 202. The lead lumen 204 may extend the length of the lead 202 from a proximal end of the lead 202 to a distal end 208 of the lead 202. The lead lumen 204 may be parallel with the central axis 144 of the catheter 102 when the lead 202 is disposed within the delivery lumen 146. For example, lead lumen 204 may be coaxial with the delivery lumen 146. The lead lumen 204 may be open at the distal end 208 of the lead 202. For example, the lead 202 may have an access opening 210 to the lead lumen 204 at the distal end 208. The lead lumen 204 may also be open at the proximal end of the lead 202 to receive a payload therein. The payload in an example is the stylet 200. In an example, the lead lumen 204 is cylindrical, with a circular cross-sectional shape. In another example, the lead lumen 204 may have an elliptical or oval shape. In this example, the lead body 206 is radially disposed between the stylet 202 and the catheter body 140. For example, the lead body 206 surrounds the stylet 202, and the catheter body 140 surrounds the lead body 206.

[0060] In the illustrated embodiment, the lead lumen 204 is sized to receive the stylet 200 therein. The stylet 200 is disposed within the lead lumen 204 in Figure 4. The lead lumen 204 is also sized to provide clearance to permit the stylet 200 to move relative to the lead 202 (and the catheter 102). With the clearance, the stylet 200 can be advanced and / or retracted relative to the lead 202. For example, if the stylet 200 has a diameter of 2 F, the lead lumen 204 may have a cross-sectional dimension (e.g., diameter) of 3 F. The clearance may reduce friction between the stylet 200 and an inner surface of the lead body 206 that defines the lead lumen 204.

[0061] Figure 4 may show the distal end segment 124 of the delivery system 100 in a routing configuration. The lead 202 is nested within the delivery lumen 146 of the catheter 102, and the stylet 200 is nested within the lead lumen 204 of the lead 202. Optionally, neither the lead 202 nor the stylet 200 projects beyond15870W0011 (013-0619PCT) 17 PATENTthe distal end 116 of the catheter 102 in the routing configuration. The routing configuration may be utilized when the delivery system 100 is being implanted into the patient and the distal end segment 124 is traversing through the vascular system to the heart. In an example, the distal end segment 124 may be advanced into a chamber of the heart, such as the right ventricle chamber, when in the routing configuration. In an alternative example, the stylet 200 and / or the lead 202 may be loaded into the delivery lumen 146 of the catheter 102 only after the catheter 102 is maneuvered through the incision of the patient and advanced at least part of the way to the heart.

[0062] Figure 5 illustrates the distal end segment 124 of the delivery system 100 with a distal end 208 of the lead 202 projecting beyond the distal end 116 of the catheter 102 and a distal end 212 of the stylet 200 projecting beyond the distal end 208 of the lead 202. The lead 202 and the stylet 200 may each be movable relative to the catheter 102. For example, an operator (e.g., a physician or other technician) operating the delivery system 100 may manipulate one or more actuators to selectively advance and retract the stylet 200 and the lead 202. The one or more actuators may be located on or near the handle 104 (Figure 3). For example, once the distal end 116 of the catheter 102 is located proximate to cardiac tissue (e.g., myocardium) near a candidate site of interest (SOI) for stimulation therapy, the operator can selectively advance the stylet 200 through the lead lumen 204 beyond the distal end 116 of the catheter 102 and the distal end 208 of the lead 202. The projecting stylet 200 may pierce the cardiac tissue and traverse through the myocardium towards one or more candidate SOIs. In one example application, the cardiac tissue pierced by the stylet 200 may be a ventricular septal wall 32 that divides the left and right ventricular chambers. The candidate SOI may be in the ventricular septal wall 32 for HBP or LBBP. In another example application, the stylet 200 may be advanced to penetrate a different area, such as the right ventricular apex.15870W0011 (013-0619PCT) 18 PATENT

[0063] After determining a target implant site in the cardiac tissue, the stylet 200 may function as a guidewire that guides the lead 202 to the target implant site. For example, with the stylet 200 embedded within the cardiac tissue, the lead 202 may be advanced through the delivery lumen 146 so that the distal end 208 of the lead 202 projects beyond the distal end 116 of the catheter 102. The operator may control the movement of the lead 202 via an actuator on or near the handle 104. The advancing distal end 208 of the lead 202 may penetrate the cardiac tissue. The movement of the distal end 208 of the lead 202 may be guided by the stylet 200 which is anchored to the cardiac tissue and projects beyond the distal end 208 of the lead 202. For example, the lead 202 continues to surround the stylet 200. The lead 202 moves along the length of the stylet 200, approaching the distal end 212 of the stylet 200.

[0064] The lead 202 may include a fixation element 214 for penetrating the cardiac tissue and securing the lead 202 to the cardiac tissue. The fixation element 214 may be a helical coil, a tapered point, or the like. The fixation is a helical element 214 in the illustrated example. In an example, the lead 202 may include a protective sleeve 216 that surrounds the fixation element 214. The protective sleeve 216 may protect the patient tissue from the fixation element 214 before the fixation element 214 is used to secure the lead 202 to the cardiac tissue. The protective sleeve 216 may also protect the fixation element 214 and / or other components of the lead 202 that are relatively delicate and fragile from risk of damage experienced outside of the patient. The protective sleeve 216 may retract to expose the fixation element 214 when the lead 202 is poised for penetration into the cardiac tissue. The protective sleeve 216 optionally may be withdrawn after implant with the catheter 102 and the stylet 200, while the lead 202 remains secured to the heart.

[0065] Although both the lead 202 and the stylet 200 are shown projecting from the catheter 102 in Figure 5, the operator can control the stylet 200 to advance beyond the distal end 116 of the catheter 102 while the distal end 208 of the lead15870W0011 (013-0619PCT) 19 PATENT202 is nested within the delivery lumen 146 of the catheter 102. For example, the stylet 200 can be used to explore candidate SOI as an active mapping wire. Furthermore, after the target implant site is determined, the stylet 200 can be used to secure the delivery system 100 to the cardiac tissue to allow the lead 202 to accurately and efficiently reach the target implant site.

[0066] The stylet 200 has a tip section 220 at the distal end 212. The tip section 220 selectively transitions between a narrow state and a flared state. The tip section 220 in the flared state has a greater lateral extension than the tip section 220 in the narrow state. The tip section 220 is shown in the narrow state in Figure 5. For example, the tip section 220 may have to be in the narrow state to fit within the lead lumen 204 of the lead 202. When in the flared state, the tip section 220 may be too wide to fit within the lead lumen 204. The state of the tip section 220 of the stylet 200 may be controlled by the operator. For example, the operator may manipulate one or more actuators on or near the handle 104 (shown in Figure 3) to selectively switch the tip section 220 between the flared and narrow states. In an example, the operator may maintain the stylet tip section 220 in the narrow state as the stylet 200 projects beyond the catheter 102 and the lead 202 and pierces the cardiac tissue of the heart. The operator may subsequently transition the tip section 220 to the flared state while the tip section 220 is within the cardiac tissue and / or a chamber of the heart to anchor the stylet 200 to the cardiac tissue.

[0067] Figure 6 is a cross-sectional view of the tip section 220 of the stylet 200 according to at least one embodiment. The cross-section plane may bisect the stylet 200 and may extend parallel to the longitudinal length or axis of the stylet 200. The tip section 220 is shown in the narrow state in Figure 6. The stylet 200 may include a core element 240 and an outer sheath 242. In the narrow state, the outer sheath 242 surrounds and contains the core element 240. The core element 240 is within a channel 244 defined by the outer sheath 242. The outer sheath 242 retains the core element 240 in a linear or straight orientation. In an example, the core element 240 is a wire, and the outer sheath 242 is a thin tube (e.g., a15870W0011 (013-0619PCT) 20 PATENThypotube). The lateral dimensions (e.g., diameter) of the tip section 220 may be significantly smaller than the lead 202.

[0068] In an example, the outer sheath 242 is retractable relative to the core element 240. For example, the outer sheath 242 can retract (e.g., slide) in a direction away from the distal end 212 of the stylet 200. The retraction of the outer sheath 242 may expose at least a portion of the core element 240 along the tip section 220, so that the core element 240 is no longer surrounded by and contained within the outer sheath 242. In an example, retraction of the outer sheath 242 may cause the stylet 200 to transition to the flared state. For example, the core element 240 may automatically transition to the flared state when left unconstrained by the retraction of the outer sheath 242. The core element 240 may be biased to automatically laterally project beyond the outer sheath 242 in response to the retraction of the outer sheath 242 to expose the core element 240. In another example, the transition to the flared state may require a two-part action of retracting the outer sheath 242 and then actuating the core element 240 to transition to a non-linear, flared orientation.

[0069] The operator (e.g., physician) may selectively retract the outer sheath 242 of the stylet 200. For example, the outer sheath 242 may extend at least most of the length of the stylet 200, and the operator may manipulate an actuator to pull the outer sheath 242 near a proximal end of the outer sheath 242, without pulling the core element 240. In use, the outer sheath 242 may remain covering the core element 240 as the tip section 220 of the stylet 200 is advanced into the cardiac tissue. As such, the stylet 200 may remain in the narrow state to penetrate the cardiac tissue. Once the operator is satisfied with the position of the stylet 200 in the cardiac tissue, the operator can switch the stylet 200 to the flared state to anchor the stylet 200 in place.

[0070] Figure 7 illustrates the tip section 220 of the stylet 200 in the flared state according to a first example embodiment of the core element 240. The stylet 220 shown in Figure 7 may represent the stylet shown in Figure 6. In Figure 7, the15870W0011 (013-0619PCT) 21 PATENTcore element 240 assumes a coiled shape in the flared state. The coiled shape may be a spiral shape. The core element 240 may coil in two dimensions along one plane, as shown, or may coil in three dimensions. In the flared state, the core element 240 laterally (e.g., radially) projects beyond the outer diameter of the outer sheath 242. The footprint of the tip section 220 expands in the flared state relative to the narrow state. Although the coiled shape is shown in Figure 7, in other examples the core element 240 may assume a different non-linear orientation in the flared state. For example, the core element 240 may assume a circular shape, an oval shape, a helical corkscrew shape, or the like. When in the flared state, the tip section 220 of the stylet 200 is broader than the portion of the stylet 200 proximal to the tip section 220. The broad tip section 220 can be used to anchor the stylet 200 to the heart.

[0071] In an example, the core element 240 may include a shape memory material. The shape memory material may be a metal alloy, such as Nitinol. In another example, the shape memory material may include a polymer. The shape memory material may have an inherent bias that causes the core element 240 to automatically assume the coiled (or otherwise non-linear) state when at least one stimulus is provided to trigger switching to the flared state. The stimulus may be retraction of the outer sheath 242. Other example stimuli, in addition to retraction of the outer sheath 242, may be application of an electrical current, heat, or the like.

[0072] In another example, the core element 240 may enlarge by expanding during the transition from the narrow state to the flared state. For example, the core element 240 may be compressed within the outer sheath 242 when in the narrow state, and the retraction of the outer sheath 242 may allow the core element 240 material to resiliently return to an uncompressed state. The core element 240 may include a foam or foam-like material.

[0073] In an example, the core element 240 may be doped with a radiopaque material at least along the tip section 220. The radiopaque material15870W0011 (013-0619PCT) 22 PATENTmay serve as a marker that can be used to visualize the stylet 200 via fluoroscopy during the implant procedure. For example, the radiopaque material may allow the operator to view the location of the tip section 220 of the stylet 200 in the heart and verify whether the stylet 200 is in the narrow state or the flared state at a given time.

[0074] Figures 8 through 11 show the lead 202 and the stylet 200 of the delivery system 100 at various stages of an implant procedure according to an example application. In the example application, the lead 202 is to be implanted into the left bundle branch within the interventricular septum, referred to herein as septal wall 32. Figure 8 shows the lead 202 and the stylet 200 at a first stage in the implant procedure. Although not shown in Figure 8, the delivery catheter 102 may be inserted into the patient and navigated through the vascular system (e.g., one or more veins) to the right ventricle chamber 280. The catheter 102 may be moved to position the distal end 116 against or proximate to a right ventricle side (e.g., a front side) 250 of the septal wall 32. The lead 202 shown in Figure 8 may be housed within the delivery lumen 146 of the catheter 102. The distal end 208 of the lead 202 is within the right ventricle chamber 280. The operator may advance the stylet 200 to project beyond the catheter 102 and the lead 202 and penetrate the septal wall 32. The stylet 200 may move through the thickness of the septal wall 32 in a direction towards the left ventricle chamber 282. In Figure 8, the distal end 212 of the stylet 200 is roughly midway through the thickness of the septal wall 32 between the right and left ventricle chambers 280, 282. The stylet 200 is in the narrow state.

[0075] In an example, the stylet 200 may be used as an active mapping wire. The stylet 200 may include an electrode 252 located at or proximate to the distal end 212. The electrode 252 may be used to define a bipolar electrode pair with a second electrode that is disposed on the catheter 102 or the lead 202. The bipolar electrode may may be used to delivery stimulation energy to the cardiac15870W0011 (013-0619PCT) 23 PATENT(e.g., myocardial) tissue and / or sense evoked responses from the cardiac tissue to evaluate a candidate SOI.

[0076] The bipolar electrode pair is used to evaluate one or more candidate SOI to determine a target implant site for the lead 202. For example, the operator may progress the stylet 200 through the septal wall 32 until the distal end 212 reaches a candidate SOI, such as within the left bundle branch area. The operator may connect the stylet 200 to a pacing system analyzer (PSA). The stylet 200 may have a terminal ring at the proximal end of the stylet 200. The terminal ring may be electrically connected to the electrode 252 at the distal end 212 via a wired connection. The wired connection may be the core element 240 itself, the outer sheath 242 itself, or a discrete wire that extends along the core element 240 and / or along the outer sheath 242. The PSA may collect data regarding capture thresholds from the bipolar electrode pair that includes the electrode 252.

[0077] After collecting the data at a first candidate SOI, the operator may move the stylet 200 to a second candidate SOI and repeat the process. For example, the stylet 200 may be moved to the second candidate SOI by simply advancing the stylet 200 farther into the septal wall 32. In another example, the operator may withdraw the stylet 200 out of the septal wall 32, then reposition the catheter 102 along the septal wall 32 at a new penetration location. At the new location, the operator may advance the stylet 200 into the septal wall 32 to penetrate the myocardial tissue. During this evaluation process, the operator may investigate a plurality of different candidate SOI. The target pacing site may be determined by comparing the data collected at each of the candidate SOI. For example, the operator may select as the target pacing site the candidate SOI that has the lowest capture threshold of the candidate SOIs. The stylet 200 has a thin, narrow footprint that does very little or no damage to the cardiac tissue during the implant site evaluation process.

[0078] Once the target pacing site is selected, the delivery system 100 is moved towards the target pacing site. If repositioning is required, the stylet 200 is15870W0011 (013-0619PCT) 24 PATENTonce again advanced into the septal wall 32. The electrode 252 of the stylet 200 may be used reconfirm the location of the target pacing site. The operator may then use the stylet 200 to anchor the delivery system 100 in place. Anchoring the delivery system 100 via the stylet 200 may allow the lead 202 to accurately and reliably reach the target pacing site. For example, the operator may advance the stylet 200 through the septal wall 32 until the distal end 212 exits the septal wall 32 and enters the left ventricle chamber 282.

[0079] Figure 9 shows the lead 202 and the stylet 200 at a second stage in the implant procedure. The lead 202 remains in the right ventricle chamber 280. The stylet 200 extends from the lead 202 through the septal wall 32 and the distal end 212 of the stylet 200 is within the left ventricle chamber 282. The tip section 220 of the stylet 200 is within the left ventricle chamber 282. The stylet 200 is still in the narrow state. The operator may then transition the stylet 200 to the flared state. For example, the operator may retract the outer sheath 242 away from the distal end 212, pulling towards the proximal end.

[0080] Figure 10 shows the lead 202 and the stylet 200 at a third stage in the implant procedure. In an example, the retraction of the outer sheath 242 may automatically cause the core element 240 at the tip section 220 to transition to the flared state. In an example, the core element 240 may wind or coil, resulting in the core element 240 laterally extending beyond the diameter of the outer sheath 242. The tip section 220 is still located in the left ventricle chamber 282. The core element 240 in Figure 10 has the coiled shape shown in Figure 7. After the tip section 220 achieves the flared state, the operator may pull the stylet 200 in a proximal direction to initiate contact between the core element 240 and the left ventricle side (e.g., back side) 256 of the septal wall 32. This contact may anchor the stylet 200 to the septal wall 32. For example, the core element 240 in the flared state may have too wide of a footprint to fit through the small aperture or channel that is formed in the septal wall 32 by the thin stylet 200 while in the narrow state.15870W0011 (013-0619PCT) 25 PATENTThe core element 240 may resist pull-out movements in the proximal direction and retain the delivery system 100 at the desired location relative to the septal wall 32.

[0081] Figure 11 shows the lead 202 and the stylet 200 at a fourth stage in the implant procedure. With the stylet 200 in the flared state anchored to the septal wall 32, the operator may then advance the lead 202 to penetrate the septal wall 32. The helical fixation element 214 may allow the lead 202 to worm through the septal wall 32 towards the target implant site. The stylet 200 functions as a support mechanism allowing the lead 202 to torque through the tissue without pulling back. The stylet 200 in an example may also function as a guide because the lead 202 surrounds the stylet 200. For example, the lead 202 is forced to follow the path defined by the stylet 200 as the lead 202 moves in a direction toward the tip section 220.

[0082] Once the lead 202 reaches the target implant site (e g., at the left bundle branch), the operator may then release the stylet 200 by transitioning the tip section 220 back to the narrow state. In an example, the operator may achieve the narrow state by advancing the outer sheath 242 in the distal direction towards the distal end 212. The outer sheath 242 may force the core element 240 to straighten out as the outer sheath 242 surrounds and conceals the portion of the core element 240 that was exposed. Once the stylet 200 is in the narrow state again, the operator may withdraw the stylet 200 through the aperture in the septal wall 32 and through the lead lumen 204 of the lead 202. Eventually, the stylet 200 exits the patient and exits the lead 202. The distal end 208 of the lead 202 may remain embedded in the septal wall 32 at the target implant site. The operator may also withdraw the catheter 102 from the patient. The operator may then finish the remaining steps of the implant procedure, such as connecting a proximal end of the lead 202 to an IMD housing and / or the like.

[0083] Returning to Figure 5, the stylet 200 in an example is an active mapping wire used to investigate different candidate SOI for determining a longterm implant location of the lead 202. The catheter 102 may include an electrode15870W0011 (013-0619PCT) 26 PATENT290, referred to herein as catheter electrode 290. The catheter electrode 290 and the electrode 252 on the stylet 200 can be used to form a bipolar electrode pair. In an example, the pacing system analyzer device 111 (shown in Figure 3) may electrically map multiple different sites of interest along a region of cardiac tissue using the electrode 252 (e.g., the bipolar electrode pair). For example, the electrode 252 may be used as a cathode, and the catheter electrode 290 may be used as an anode. The pacing system analyzer device 111 may control a pulse generator to deliver stimulation energy through the electrode 252 of the stylet 200 to each SOI. The one or more processors may control sensing circuitry to sense an evoked response at each SOI in response to the stimulation energy that is delivered from the electrode 252. The candidate SOI may be atrial pacing sites, HIS pacing sites, left bundle branch pacing sites, right bundle branch pacing sites, and / or pacing sites proximate to the LV Purkinje fibers. By using the electrodes on the catheter 102 and the stylet 200, the lead 202 may not be used during the electrical mapping investigation. Optionally, the lead 202 may not be disposed within the catheter lumen 146 during the mapping investigation.

[0084] In an alternative embodiment, the catheter 102 may lack an electrode at the distal end segment. In that case, a bipolar electrode pair for electrical mapping of multiple candidate SOI may be formed by the electrode 252 on the stylet 200 and an electrode at the distal end of the lead 202.

[0085] Additionally or alternatively, the processes described herein may be implemented utilizing all or portions of the structural and / or functional aspects of the methods and systems described in co-pending application 17 / 007,696, filed August 31 , 2020 and titled “SYSTEMS AND METHODS FOR IMPLANTING A MEDICAL DEVICE USING AN ACTIVE GUIDEWIRE”, the complete subject matter of which is expressly incorporated herein by reference in its entirety.

[0086] Figure 12 illustrates the stylet 200 projecting from the distal end 208 of the lead 202 according to a second embodiment of the stylet 200. Figure 13 is an enlarged view of the tip section 220 of the stylet 200 shown in Figure 12. The15870W0011 (013-0619PCT) 27 PATENTstylet 200 in Figures 12 and 13 has the outer sheath 242 that surrounds the core element 240, similar to the embodiment shown in Figures 6 through 11 . The stylet 200 in Figures 12 and 13 transitions between narrow and flared states based on relative movement of the outer sheath 242 and the core element 240. Figures 12 and 13 show the tip section 220 in the flared state. The outer sheath 242 in Figures 12 and 13 may be the same as the outer sheath 242 in Figures 6 through 11 . The core element 240 in Figures 12 and 13 includes multiple prongs 302 that are biased to spread apart in different directions when transitioning from the narrow state to the flared state. For example, in the narrow state, the prongs 302 are held in close proximity to one another by the outer sheath 242. Once the outer sheath 242 is retracted to expose the core element 240, the prongs 302 are free to move away from one another. As a result, the core element 240 in the flared state laterally extends beyond the outer sheath 242. The prongs 302 may unwind, deflect, or the like. In the illustrated embodiment, the prongs 302 have a curvature and resemble a grappling hook. The prongs 302 may abut against the left ventricle side 256 of the septal wall 32 when deployed in the flared state to anchor the stylet 200 to the septal wall 32. Although two prongs 302 are shown in Figures 12 and 13, the core element 240 may have a single prong or more than two prongs 302 in other embodiments. In an example, the core element 240 has three prongs 302. In another example, the core element 240 has four prongs 302.

[0087] Figure 14 illustrates the stylet 200 of the delivery system 100 according to a third embodiment showing the tip section 220 in the narrow state. Figure 15 illustrates the stylet 200 of Figure 14 showing the tip section 220 in the flared state. The stylet 200 selectively transitions between the narrow and flared states to selectively anchor the stylet 200 to the cardiac tissue. For example, the stylet 200 in Figures 14 and 15 may replace the stylet 200 shown in Figures 6 through 11 and the stylet 200 shown in Figures 12 and 13. The stylet 200 in Figures 14 and 15 does not include an outer sheath that surrounds a core element. The stylet 200 includes a balloon 310 at the tip section 220. The balloon 310 is selectively inflatable. For example, the balloon 310 is deflated in the narrow state,15870W0011 (013-0619PCT) 28 PATENTas shown in Figure 14. The balloon 310 is inflated in the flared state, as shown in Figure 15. The operator selectively inflates the balloon 310 to transition the tip section 220 from the narrow state to the flared state, and deflates the balloon 310 to transition back to the narrow state.

[0088] The balloon 310 may be an annular balloon that is designed to significantly radially expand when inflated without significantly expanding along a longitudinal dimension (e.g., along the length of the stylet 200). The balloon 310 may be secured to a body 312 of the stylet 200 at the distal end 212. In an example, the inflated balloon 310 may have a relatively flat distal surface that is approximately flush with a distal surface 314 of the stylet body 312. A tube or channel within the body 312 may fluidly connect the balloon 310 to a port at or proximal to a proximal end of the stylet 200. The operator may selectively inject a fluid (e.g., gas or liquid) into the balloon 310 through the tube to inflate the balloon 310 and transition the tip section 220 to the flared state for anchoring the stylet 200 to the cardiac tissue. For example, the inflated balloon 310 as shown in Figure 15 may abut against the left ventricle side 256 of the septal wall 32, which resists pull-back forces on the stylet 200 (and the delivery system 100 in general).

[0089] In an example, the balloon 310 may be inflated by injecting a contrast solution into the balloon 310. The contrast solution may include a contrast element that is designed to be visible in medical images. For example, the contrast element may be visible in X-ray imaging. The contrast solution may enable the physician or other technician to easily view the distal end 212 of the stylet 200 in a medical image even while the distal end 212 is within the heart.

[0090] Figure 16 illustrates the distal end segment 124 of the delivery system 100 according to a second embodiment of the catheter 102. The lead 202 may be unchanged. The stylet 200 may be any of the stylets 200 described herein. In the illustrated embodiment, the catheter 102 defines two discrete lumens. The delivery lumen 146 that accommodates the lead 202 (or a leadless IMD) is a first delivery lumen 146. The catheter 102 also defines a second delivery lumen 330.15870W0011 (013-0619PCT) 29 PATENTThe second delivery lumen 330 is sized to accommodate the stylet 200. The second delivery lumen 330 is laterally spaced apart from the first delivery lumen 146. The second delivery lumen 330 may have a smaller cross-sectional size than the first delivery lumen 146. A portion of the catheter body 140 may separate the two lumens 146, 330. The catheter 102 shown in Figure 16 may be used if the lead 202 and / or the IMD that is to be implanted at the target implant site does not define a lumen capable of receiving the stylet 200 therethrough. In the illustrated embodiment, the stylet 200 may not interact with the lead 202. For example, the stylet 200 may not physically contact the lead 202. The stylet 200 may not function as a guidewire for the lead 202 in the illustrated embodiment.

[0091] Figure 17 is a flow chart of a method 400 of implanting a lead or an IMD within cardiac tissue of a patient according to an embodiment. The method 400 may use the delivery system 100 described in Figures 1 through 16. In different embodiments, the method may include different steps not shown in Figure 17, may omit one or more of the steps shown in Figure 17, and / or may have a different order of the steps than shown in Figure 17.

[0092] At step 402, a catheter 102 is loaded into a patient proximate to cardiac tissue at a site of interest (SOI). The catheter 102 defines a delivery lumen 146 therethrough. The SOI represents a candidate implant location for delivering pacing therapy. The SOI may be within the left bundle branch area within the interventricular septal wall 32.

[0093] At step 404, a stylet 200 is advanced through the delivery lumen 146 of the catheter 102 so that a distal end 212 of the stylet 200 projects beyond a distal end 116 of the catheter 102 and pierces the cardiac tissue at the SOI. In an example, the stylet 200 is disposed within a lead lumen 204 of a lead 202 that is located within the delivery lumen 146. The stylet 200 includes a tip section 220 at the distal end 212 that is configured to selectively transition between a narrow state and a flared state. The tip section 220 in the flared state has a greater lateral extension than the tip section in the narrow state. The tip section 220 is in the15870W0011 (013-0619PCT) 30 PATENTnarrow state when advancing through the delivery lumen 146 and penetrating the cardiac tissue.

[0094] At step 406, the tip section 220 transitions (from the narrow state) to the flared state to anchor the stylet 200 to the cardiac tissue. In an example, the stylet 200 includes a core element 240 and an outer sheath 242 that surrounds and contains the core element 240 in the narrow state of the tip section 220. Transitioning the tip section 220 to the flared state may include retracting the outer sheath 242 relative to the distal end 212 of the stylet 200 to expose the core element 240 and permit the tip section 220 to transition to the flared state. In another example, the stylet 200 includes a balloon 310 at the tip section 220. Transitioning the tip section 220 to the flared state may include inflating the balloon 310.

[0095] In an example use case, advancing the stylet 200 to pierce the cardiac tissue at the SOI may include advancing the distal end 212 of the stylet 200 through a thickness of a septal wall 32 so that the distal end 212 enters a chamber. The chamber may be a left ventricle chamber 282. In this example, the tip section 220 may transition to the flared state within the chamber so that the tip section 220 in the flared state can abut against a back side 256 of the septal wall 32.

[0096] At step 408, the lead 202 is advanced relative to the catheter 102 into the cardiac tissue, while the stylet 200 is anchored to the cardiac (e.g., myocardial) tissue. The stylet 200 may secure the delivery system 100 to the heart, resisting pull-back forces as the lead 202 advances into the cardiac tissue. In the example in which the lead 202 surrounds the stylet 200, the distal end 208 of the lead 202 follows a path defined by the stylet 200 through the cardiac tissue.

[0097] At step 410, the tip section 220 of the stylet 200 transitions (from the flared state) to the narrow state after the lead 202 is advanced into the cardiac tissue to the SOI. The tip section 220 may transition to the narrow state by15870W0011 (013-0619PCT) 31 PATENTadvancing the outer sheath 242 relative to the core element 240, deflating the balloon 310, or the like.

[0098] At step 412, the stylet 200 in the narrow state is withdrawn from the cardiac tissue. For example, if the SOI is selected as the target implant location, once the lead 202 reaches the SOI, the stylet 200 can be withdrawn entirely. The stylet 200 may be withdrawn through the delivery lumen 146 of the catheter 102 (and optionally the lead lumen 204 of the lead 202) while the distal end 208 of the lead 202 remains in the cardiac tissue at the target implant location. The catheter 102 and the stylet 200 may be withdrawn from the patient to allow the operator to complete the IMD implant procedure, such as by connecting the lead 202 to an IMD housing (or can).

[0099] Figure 18 illustrates a block diagram of an exemplary IMD that is configured to be implanted into the patient in accordance with embodiments herein. The IMD 600 may treat both fast and slow arrhythmias with stimulation therapy, including cardioversion, pacing stimulation, an implantable cardioverter defibrillator, suspend tachycardia detection, tachyarrhythmia therapy, and / or the like.

[0100] The IMD 600 has a housing 661 to hold the electronic / computing components. A proximal end of the lead 202 may connect to the housing 661 of the IMD 600. The housing 661 (which is often referred to as the “can,” “case,” “encasing,” or “case electrode”) may be programmably selected to act as the return electrode for certain stimulus modes. The housing 661 further includes a connector (not shown) with a plurality of terminals 601 , 602, 604, 606, 608, and 610. The terminals may be connected to one or more leads (e.g., lead 202) that are located in various locations within and about the heart. Each lead may have one or more electrodes. The type and location of each electrode may vary. For example, the electrodes may include various combinations of ring, tip, coil, shocking electrodes, and the like.15870W0011 (013-0619PCT) 32 PATENT

[0101] The IMD 600 includes a programmable microcontroller 620 that controls various operations of the IMD 600, including cardiac monitoring and stimulation therapy. The microcontroller 620 includes a microprocessor (or equivalent control circuitry), one or more processors, RAM and / or ROM memory, logic and timing circuitry, state machine circuitry, and I / O circuitry. The IMD 600 further includes a pulse generator 622 that generates stimulation pulses for connecting the desired electrodes to the appropriate I / O circuits, thereby facilitating electrode programmability. The switch 626 is controlled by a control signal 628 from the microcontroller 620.

[0102] Optionally, the IMD 600 may include multiple pulse generators, similar to the pulse generator 622, where each pulse generator is coupled to one or more leads / electrodes and controlled by the microcontroller 620 to deliver select stimulus pulse(s) to the corresponding one or more electrodes. The IMD 600 includes sensing circuit 644 selectively coupled to one or more electrodes that perform sensing operations, through the switch 626 to detect the presence of cardiac activity in the chamber of the heart. The output of the sensing circuit 644 is connected to the microcontroller 620 which, in turn, triggers, or inhibits the pulse generator 622 in response to the absence or presence of cardiac activity. The sensing circuit 644 receives a control signal 646 from the microcontroller 620 for purposes of controlling the gain, threshold, polarization charge removal circuitry (not shown), and the timing of any blocking circuitry (not shown) coupled to the inputs of the sensing circuit 624.

[0103] In the example of Figure 18, the sensing circuit 644 is illustrated. Optionally, the IMD 600 may include multiple sensing circuits 644, where each sensing circuit is coupled to one or more leads / electrodes and controlled by the microcontroller 620 to sense electrical activity detected at the corresponding one or more electrodes. The sensing circuit 624 may operate in, for example, a unipolar sensing configuration or a bipolar sensing configuration.15870W0011 (013-0619PCT) 33 PATENT

[0104] The IMD 600 further includes an analog-to-digital (A / D) data acquisition system (DAS) 650 coupled to one or more electrodes via the switch 626 to sample cardiac signals across any pair of desired electrodes. The A / D converter 650 is configured to acquire intracardiac electrogram signals, convert the raw analog data into digital data and store the digital data for later processing and / or telemetric transmission to an external device 690 (e.g., a programmer, local transceiver, or a diagnostic system analyzer). The A / D converter 650 is controlled by a control signal 656 from the microcontroller 620.

[0105] The microcontroller 620 is operably coupled to a memory 660 by a suitable data / address bus 662. The programmable operating parameters used by the microcontroller 620 are stored in the memory 660 and used to customize the operation of the IMD 600 to suit the needs of a particular patient. The operating parameters of the IMD 600 may be non-invasively programmed into the memory 660 through a telemetry circuit 664 in telemetric communication via communication link 667 (e.g., MICS, Bluetooth low energy, and / or the like) with the external device 690.

[0106] The IMD 600 can further include one or more physiological sensors 670. Such sensors are commonly referred to as “rate-responsive” sensors because they are typically used to adjust pacing stimulation rates according to the exercise state of the patient. However, the physiological sensor 670 may further be used to detect changes in cardiac output, changes in the physiological condition of the heart, or diurnal changes in activity (e.g., detecting sleep and wake states). Signals generated by the physiological sensors 670 are passed to the microcontroller 620 for analysis. While shown as being included within the IMD 600, the physiological sensor(s) 670 may be external to the IMD 600, yet still, be implanted within or carried by the patient. Examples of physiological sensors might include sensors that, for example, sense respiration rate, pH of blood, ventricular gradient, activity, position / posture, minute ventilation, and / or the like.15870W0011 (013-0619PCT) 34 PATENT

[0107] A battery 672 provides operating power to all of the components in the IMD 600. The battery 672 is capable of operating at low current drains for long periods of time, and is capable of providing a high-current pulses (for capacitor charging) when the patient requires a shock pulse (e.g., in excess of 2 A, at voltages above 2 V, for periods of 10 seconds or more). The battery 672 also desirably has a predictable discharge characteristic so that elective replacement time can be detected. As one example, the IMD 600 employs lithium / silver vanadium oxide batteries.

[0108] The IMD 600 further includes an impedance measuring circuit 674, which can be used for many things, including sensing respiration phase. The impedance measuring circuit 674 is coupled to the switch 626 so that any desired electrode and / or terminal may be used to measure impedance in connection with monitoring respiration phase. The IMD 600 is further equipped with a communication modem (modulator / demodulator) 640 to enable wireless communication with other devices, implanted devices and / or external devices. In one implementation, the communication modem 640 may use high frequency modulation of a signal transmitted between a pair of electrodes. As one example, the signals may be transmitted in a high frequency range of approximately 10-80 kHz, as such signals travel through the body tissue and fluids without stimulating the heart or being felt by the patient.

[0109] Optionally, the microcontroller 620 may control a shocking circuit 680 by way of a timing control 632. The shocking circuit 680 generates shocking pulses as controlled by the microcontroller 620. The shocking circuit 680 may be controlled by the microcontroller 620 by a control signal 682.

[0110] Although not shown, the microcontroller 620 may further include other dedicated circuitry and / or firmware / software components that assist in monitoring various conditions of the patient's heart and managing pacing therapies. The microcontroller 620 further includes a timing control 632, an arrhythmia detector 634, a morphology detector 636 and multi-phase therapy15870W0011 (013-0619PCT) 35 PATENTcontroller 633. The timing control 632 is used to control various timing parameters, such as stimulation pulses (e.g., pacing rate, atria-ventricular (AV) delay, atrial interconduction (A-A) delay, ventricular interconduction (V-V) delay, etc.) as well as to keep track of the timing of RR-intervals, refractory periods, blanking intervals, noise detection windows, evoked response windows, alert intervals, marker channel timing, and the like.

[0111] The morphology detector 636 is configured to review and analyze one or more features of the morphology of cardiac activity signals. For example, in accordance with embodiments herein, the morphology detector 636 may analyze the morphology of detected R waves, where such morphology is then utilized to determine whether to include or exclude one or more beats from further analysis. For example, the morphology detector 636 may be utilized to identify nonconducted ventricular events, such as ventricular fibrillation and the like.

[0112] The arrhythmia detector 634 may be configured to apply one or more arrhythmia detection algorithms for detecting arrhythmia conditions. By way of example, the arrhythmia detector 634 may apply various detection algorithms. The arrhythmia detector 634 may be configured to declare a ventricular fibrillation episode based on the cardiac events.

[0113] The therapy controller 633 is configured to perform the operations described herein. The therapy controller 633 is configured to identify a multi-phase therapy based on the ventricular fibrillation episode, the multi-phase therapy including a pacing therapy. The therapy controller 633 is configured to manage delivery of the burst pacing therapy at a pacing site in a coordinated manner after the one or more shocks. The pacing site may be located at a target SOI, such as a His Bundle. Optionally, other pacing sites may be located at one of a left ventricular (LV) site or a right ventricular (RV) site. The therapy controller 633 may manage delivery of the shock along a shocking vector between shocking electrodes.15870W0011 (013-0619PCT) 36 PATENT

[0114] The delivery system in an example application uses the stylet (e.g., positioning stylet) to allow the cardiac lead to align through the septal wall between the right and left ventricle. The flared distal tip section of the stylet may anchor the delivery system to the septal wall by fixating against the left ventricular side of the septal wall. The stylet may provide a pathway for the lead through the septal wall with little to no interference from the tissue due to the anchoring of the stylet against the left ventricular side of the septal wall. For example, the lead may not progress through the entire thickness of the septal wall, so the lead does not experience any interference caused by the flared tip section disposed within the left ventricle chamber.

[0115] In an example, the positioning stylet may be introduced through the lumen of the lead to advance beyond the distal end of the lead and pierce the cardiac tissue. The stylet proceeds into the myocardial tissue. An electrode at the distal end of the stylet may assist with determining the target pacing site for stimulation therapy. Once the target pacing site is determined, the stylet may be advanced, by the physician or other technician, farther through the septal wall to enter the left ventricle chamber. The stylet is in the narrow state during these activities. Once the stylet fully extends through the thickness of the septal wall and the tip section is located within the left ventricle chamber, the physician may actuate the stylet to transition the tip section to the flared state for anchoring the stylet.

[0116] The transition may involve retracting an outer sheath of the stylet to expose a core element of the stylet. The core element is contained within the outer sheath in the narrow state of the stylet, when the tip section is linear or straight. Once the outer sheath is retracted, the core element is configured to deviate from a linear orientation to achieve the flared state. As examples, the core element in the flared state may have a spiral or loop shape that laterally extends beyond the perimeter of the outer sheath. The core element in the flared state may abut against the left ventricular side of the septal wall to anchor the stylet in place. For15870W0011 (013-0619PCT) 37 PATENTexample, the flared core element may have a lateral footprint that is larger than the size of the channel formed through the septal wall by the stylet. The flared core element may prohibit the stylet from being pulled or otherwise moving in a retracting direction out of the septal wall into the right ventricle cavity. While the stylet is anchored to the septal wall, the physician can progress the lead from the right ventricle chamber into the septal wall along the length of the stylet to the selected target pacing site. The anchoring of the stylet assists with the lead implant because the stylet guides the movement of the lead and secures the entire delivery system in place relative to the septal wall. For example, the stylet in the flared state reduces the risk of the stylet being unintentionally moved in a retraction direction within the channel, or even being pulled entirely out of the channel, before the lead reaches the target pacing site. Either scenario may result in the lead failing to reach the target pacing site.

[0117] Once the lead reaches the target pacing site in the thickness of the septal wall, the style may transition from the flared state to the narrow state to release the stylet from the anchoring configuration. For example, the physician may move the outer sheath in a distal direction to encapsulate the core element and force the core element to assume the linear orientation. With the stylet in the narrow state, and the lead located at the target pacing site, the stylet can be withdrawn in a proximal direction relative to the lead. The stylet may be pulled so that the tip section exits the left ventricle chamber into the channel formed in the septal wall. The tip section of the stylet may then travel through the lumen of the lead, while the lead remains secured to the septal wall, to withdraw the stylet from the lead and the patient.

[0118] Reference throughout this specification to “one embodiment” or “an embodiment” (or the like) means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment. Thus, appearances of the phrases “in one embodiment” or “in15870W0011 (013-0619PCT) 38 PATENTan embodiment” or the like in various places throughout this specification are not necessarily all referring to the same embodiment.

[0119] The term “sized” as used herein is not limited to the act of manufacturing, but rather refers to a dimension similar to length, width, volume, etc. A lumen being sized to accommodate a specific component is not a method operation, but rather a characteristic of the lumen.

[0120] It is to be understood that the above description is intended to be illustrative, and not restrictive. For example, the above-described embodiments (and / or aspects thereof) may be used in combination with each other. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the inventive subject matter without departing from its scope. While the dimensions and types of materials described herein are intended to define the parameters of the inventive subject matter, they are by no means limiting and are exemplary embodiments. Many other embodiments will be apparent to one of ordinary skill in the art upon reviewing the above description. The scope of the inventive subject matter should, therefore, be determined with reference to the appended claims, along with the full scope of equivalents to which such claims are entitled. In the appended claims, the terms “including” and “in which” are used as the plain-English equivalents of the respective terms “comprising” and “wherein.” Moreover, in the following claims, the terms “first,” “second,” and “third,” etc. are used merely as labels, and are not intended to impose numerical requirements on their objects. Further, the limitations of the following claims are not written in means-plus-function format and are not intended to be interpreted based on 35 U.S.C. § 112(f) unless and until such claim limitations expressly use the phrase “means for” followed by a statement of function void of further structure.15870W0011 (013-0619PCT) 39 PATENT

Claims

WHAT IS CLAIMED IS:1 . A delivery system, comprising: a catheter (102) defining a delivery lumen (146) therethrough; and a stylet (200) configured to extend through the delivery lumen (146) of the catheter (102) and movable relative to the catheter (102), the stylet (200) including a tip section (220) at a distal end (212) of the stylet (200), the tip section (220) configured to selectively transition between a narrow state and a flared state, wherein the tip section (220) in the flared state has a greater lateral extension than the tip section (220) in the narrow state, wherein the tip section (220) in the narrow state is configured to project beyond a distal end (116) of the catheter (102) to pierce cardiac tissue, and the tip section (220) is configured to transition from the narrow state to the flared state to anchor the stylet (200) to the cardiac tissue.

2. The delivery system of claim 1 , further comprising a lead (202) of an implantable medical device (IMD) (50, 600), the lead (202) including a lead body (206) that defines a lead lumen (204) therethrough, wherein the stylet (200) is configured to extend through the lead lumen (204) of the lead (202) and is movable relative to the lead (202), and the lead (202) is configured to extend through the delivery lumen (146) of the catheter (102) and is movable relative to the catheter (102).

3. The delivery system of claim 2, wherein, while the stylet (200) is anchored to the cardiac tissue via the tip section (220) in the flared state, the lead (202) is configured to be advanced relative to the catheter (102) along a length of the stylet (200) so that a distal end (208) of the lead (202) penetrates the cardiac tissue and follows a path defined by the stylet (200) through the cardiac tissue.15870W0011 (013-0619PCT) 40 PATENT4. The delivery system of claim 1 , wherein the stylet (200) includes an electrode (252) located one of on the tip section (220) or proximate to the tip section (220).

5. The delivery system of claim 4, wherein the electrode (252) on the stylet (200) is configured to define a bipolar electrode pair with a second electrode (290) that is disposed on one of the catheter (102) or an IMD (50, 600) that is held by the catheter (102), the bipolar electrode pair configured to at least one of deliver stimulation energy to the cardiac tissue or sense evoked responses from the cardiac tissue to evaluate a site of interest (SOI) along the cardiac tissue.

6. The delivery system of claim 1 , wherein the stylet (200) includes a core element (240) and an outer sheath (242) that surrounds and contains the core element (240) in the narrow state of the tip section (220), wherein the outer sheath (242) is retractable relative to the distal end (212) of the stylet (200) to expose the core element (240) and permit the tip section (220) to transition to the flared state.

7. The delivery system of claim 6, wherein the core element (240) is biased to automatically laterally project beyond the outer sheath (242), achieving the flared state, in response to retraction of the outer sheath (242) to expose the core element (240).

8. The delivery system of claim 7, wherein the core element (240) comprises a shape memory material.

9. The delivery system of claim 7, wherein the core element (240) is configured to automatically assume a coiled shape in the flared state.

10. The delivery system of claim 7, wherein the core element (240) includes multiple prongs (302) that are biased to spread apart in different directions when transitioning from the narrow state to the flared state.15870W0011 (013-0619PCT) 41 PATENT11. The delivery system of claim 1 , wherein the stylet (200) includes a balloon (310) at the tip section (220), the balloon (310) configured to be inflated to transition the tip section (220) from the narrow state to the flared state.

12. The delivery system of claim 1 , wherein the delivery lumen (146) of the catheter (102) is a first delivery lumen (146), and the catheter (102) defines a second delivery lumen (330) laterally spaced apart from the first delivery lumen (146), the second delivery lumen (330) having a greater cross-sectional size than the first delivery lumen (146), the second delivery lumen (330) configured to receive at least a portion of an IMD (50, 600) that is movable through the second delivery lumen (330) relative to the catheter (102).

13. A method comprising: loading a catheter (102) into a patient towards cardiac tissue at a site of interest (SOI), the catheter (102) defining a delivery lumen (146) therethrough; advancing a stylet (200) through the delivery lumen (146) of the catheter (102) so that a distal end (212) of the stylet (200) projects beyond a distal end (116) of the catheter (102) and pierces the cardiac tissue at the SOI, the stylet (200) including a tip section (220) at the distal end (212) that is configured to selectively transition between a narrow state and a flared state, wherein the tip section (220) in the flared state has a greater lateral extension than the tip section (220) in the narrow state, and the tip section (220) is in the narrow state when advancing through the delivery lumen (146) and piercing the cardiac tissue; and transitioning the tip section (220) to the flared state to anchor the stylet (200) to the cardiac tissue.

14. The method of claim 13, wherein the stylet (200) extends through a lead lumen (204) of a lead (202) of an IMD (50, 600) and is movable relative to the lead (202), the lead (202) extending through the delivery lumen (146) of the catheter15870W0011 (013-0619PCT) 42 PATENT(102) and movable relative to the catheter (102), wherein the method further comprises: advancing the lead (202) relative to the catheter (102) along a length of the stylet (200), while the stylet (200) is anchored to the cardiac tissue, so that a distal end (208) of the lead (202) penetrates the cardiac tissue and follows a path defined by the stylet (200) through the cardiac tissue.

15. The method of claim 14, further comprising: transitioning the tip section (220) of the stylet (200) to the narrow state after advancing the lead (202) into the cardiac tissue; and withdrawing the stylet (200) in the narrow state from the cardiac tissue through the lead lumen (204) of the lead (202) while the distal end (208) of the lead (202) remains in the cardiac tissue.

16. The method of claim 13, wherein advancing the stylet (200) to pierce the cardiac tissue at the SOI comprises advancing the distal end (212) of the stylet (200) through a thickness of a septal wall (32) so that the distal end (212) enters a chamber (282), and transitioning the tip section (220) to the flared state comprises transitioning the tip section (220) to the flared state within the chamber (282) so that the tip section (220) in the flared state is configured to abut against a back side (256) of the septal wall (32).

17. The method of claim 13, wherein the stylet (200) includes a core element (240) and an outer sheath (242) that surrounds and contains the core element (240) in the narrow state of the tip section (220), wherein transitioning the tip section (220) to the flared state comprises retracting the outer sheath (242) relative to the distal end (212) of the stylet (200) to expose the core element (240) and permit the tip section (220) to transition to the flared state.15870W0011 (013-0619PCT) 43 PATENT18. The method of claim 13, wherein the stylet (200) includes a balloon (310) at the tip section (220), and wherein transitioning the tip section (220) to the flared state comprises inflating the balloon (310).

19. A delivery system comprising: a lead (202) of an implantable medical device (IMD) (50, 600), the lead (202) including a lead body (206) that defines a lead lumen (204) therethrough; and a stylet (200) configured to extend through the lead lumen (204) of the lead (202) and movable relative to the lead (202), the stylet (200) including a tip section (220) at a distal end (212) of the stylet (200), the tip section (220) configured to selectively transition between a narrow state and a flared state, wherein the tip section (220) in the flared state has a greater lateral extension than the tip section (220) in the narrow state, wherein the tip section (220) in the narrow state is configured to project beyond a distal end (208) of the lead (202) to pierce cardiac tissue of a heart at a site of interest (SOI), wherein the tip section (220) is configured to transition from the narrow state to the flared state while the tip section (220) is within the heart to anchor the stylet (200) to the heart, and wherein the lead (202) is configured to be advanced into the cardiac tissue while the stylet (200) is anchored to the heart so that the lead (202) follows a path defined by the stylet (200) through the cardiac tissue.

20. The delivery system of claim 19, wherein the stylet (200) includes a core element (240) and an outer sheath (242) that surrounds and contains the core element (240) in the narrow state of the tip section (220), wherein the outer sheath (242) is retractable relative to the distal end (212) of the stylet (200) to expose the15870W0011 (013-0619PCT) 44 PATENTcore element (240), wherein the core element (240) is biased to automatically laterally project beyond the outer sheath (242), achieving the flared state, in response to retraction of the outer sheath (242) to expose the core element (240).

21. The delivery system of claim 19, further comprising a catheter (102) defining a delivery lumen (146) therethrough, wherein the lead (202) is configured to extend through the delivery lumen (146) of the catheter (102) and is movable relative to the catheter (102), wherein the tip section (220) of the stylet (200) in the narrow state is configured to project beyond the distal end (208) of the lead (202) and a distal end (116) of the catheter (102) to pierce the cardiac tissue at the SOI.

22. The delivery system of claim 19, wherein the stylet (200) includes an electrode (252) located one of on the tip section (220) or proximate to the tip section (220), and the electrode (252) is configured to define a bipolar electrode pair with a second electrode (290) that is disposed on one of the lead (202) or a catheter (102) that holds the lead (202), the bipolar electrode pair configured to at least one of deliver stimulation energy to the cardiac tissue or sense evoked responses from the cardiac tissue to evaluate the SOI.15870W0011 (013-0619PCT) 45 PATENT

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