Force Sensing Mechanism for Contact Detection in a Catheter System

Abstract

The catheter comprises a shaft and a distal end portion that extends distally from the distal end of the shaft and defines a longitudinal axis. The distal end portion includes a proximal segment, a distal segment that is located distally of the proximal segment and is displaceable relative to the proximal segment, and a force sensing mechanism. The force sensing mechanism includes a proximal housing fixed within the proximal segment, a piezoelectric sensor attached to the proximal housing, the piezoelectric sensor having a first portion fixedly attached to the proximal housing and a second portion not fixedly attached to the proximal housing, and a distal housing fixed within the distal segment, the distal housing including a protrusion configured to contact the second portion of the piezoelectric sensor and apply an axial force to the second portion of the piezoelectric sensor when an external force is applied to the distal segment.

Description

Technical Field

[0001] The present disclosure generally relates to features of various force sensing catheters.

Background Art

[0002] In ablation therapy, it may be useful to evaluate the contact between the ablation element and the tissue to be ablated. In interventional cardiac electrophysiology (EP) procedures, for example, contact can be used to evaluate the effectiveness of the ablation therapy being performed. By knowing whether a part of the catheter is in contact with the target tissue and to what extent a part of the catheter is compressing the target tissue, other treatments and diagnoses using the catheter can be assisted. The tissue exerts a force back on the catheter, and by measuring this force, the contact and the degree to which the catheter compresses the target tissue can be evaluated.

[0003] There is a continuing need for improved catheter devices capable of sensing the force exerted by the catheter tip on the target tissue, and corresponding methods of use.

Summary of the Invention

[0004] In Example 1, the catheter is adapted to measure contact force and includes an elongate shaft having a proximal end and a distal end, and a distal end portion extending distally from the distal end of the shaft. The distal end portion defines a longitudinal axis extending therethrough and includes a proximal segment, a distal segment positioned distal to the proximal segment and spaced apart from the proximal segment with a gap therebetween, and a force sensing mechanism. The force sensing mechanism includes a proximal housing fixed within the proximal segment, a piezoelectric sensor attached to the proximal housing and having a first portion fixedly attached to the proximal housing and a second portion not fixedly attached to the proximal housing, and a distal housing fixed within the distal segment, the distal housing contacting the second portion of the piezoelectric sensor and including a protrusion configured to apply an axial force to the second portion of the piezoelectric sensor when an external force is applied to the distal segment. The piezoelectric sensor is configured to generate an output indicative of the amount of axial force applied to the second portion of the piezoelectric sensor in response to an external force applied to the distal segment.

[0005] In Example 2, in the catheter of Example 1, the proximal housing includes an upper surface, a lower surface, and a cavity extending from the lower surface through the upper surface, the first portion of the piezoelectric sensor is fixedly attached to the upper surface, and the second portion of the piezoelectric sensor extends at least partially across the cavity.

[0006] In Example 3, in the catheter of Example 2, the piezoelectric sensor has an arcuate or rectangular outer shape when viewed in a direction parallel to the longitudinal axis. In Example 4, in the catheter of Example 2, the piezoelectric sensor has an annular shape when viewed in a direction parallel to the longitudinal axis, the first portion is an outer peripheral portion of the piezoelectric sensor, and the second portion is located radially inward of the first portion of the piezoelectric sensor.

[0007] In Example 5, in the catheter of Example 2, the piezoelectric sensor is a substantially circular disk, and the second portion extends across the cavity. In Example 6, in any of the catheters of Examples 1 - 5, the proximal housing is disposed within a part of the cavity and includes a compressible backing material that contacts a second portion of the piezoelectric sensor on the side opposite to the protrusion on the distal housing, and the backing material resists deformation of the second portion of the piezoelectric sensor when an external force is applied to the distal segment.

[0008] In Example 7, in any of the catheters of Examples 1 - 6, the force sensing mechanism is attached to the proximal housing and includes three piezoelectric sensors spaced circumferentially about the longitudinal axis, and each of the three piezoelectric sensors has a first portion fixedly attached to the proximal housing and a second portion deflectable relative to the first portion.

[0009] In Example 8, in the catheter of Example 7, the distal housing includes three protrusions, each protrusion contacts a corresponding second portion of one of the three piezoelectric sensors, and is configured to apply an axial force to the second portion of the corresponding piezoelectric sensor when an external force is applied to the distal segment.

[0010] In Example 9, in the catheter of Example 8, each of the three piezoelectric sensors is configured to generate an output indicative of the amount of axial force applied to the second portion of the piezoelectric sensor in response to an external force applied to the distal segment.

[0011] In Example 10, in the catheter of Example 9, the proximal housing includes three cavities extending from the bottom surface through the top surface, each of the three cavities is aligned with a corresponding one of the three piezoelectric sensors, and the second portion of each of the three piezoelectric sensors extends at least partially across a corresponding one of the three cavities.

[0012] In Example 11, in the catheter of Example 10, each piezoelectric sensor has an arcuate or rectangular outer shape when viewed in a direction parallel to the longitudinal axis. In Example 12, in the catheter of Example 10, each piezoelectric sensor has an annular shape when viewed from a direction parallel to the longitudinal axis, the first portion is the outer peripheral portion of the piezoelectric sensor, and the second portion is located radially inward of the first portion of the piezoelectric sensor.

[0013] In Example 13, in the catheter of Example 10, each piezoelectric sensor is a substantially circular disk, and the second portion of each piezoelectric sensor extends across the corresponding cavity. In Example 14, in any of the catheters of Examples 8 to 13, a compressible backing material is disposed within a part of each cavity and contacts the second portion of the corresponding piezoelectric sensor on the side opposite to the corresponding protrusion on the distal housing, and the backing material resists deformation of the second portion of the corresponding piezoelectric sensor when an external force is applied to the distal segment.

[0014] In Example 15, the catheter of Example 1 further comprises a preloading mechanism operably coupled to the proximal housing and configured to enable a user to selectively apply a preload to the piezoelectric sensor.

[0015] In Example 16, the catheter is adapted to measure a contact force, and the catheter comprises an elongate shaft having a proximal end and a distal end, and a distal end portion extending distally from the distal end of the shaft. The distal end portion defines a longitudinal axis extending therethrough, and comprises a proximal segment, a distal segment located distally of the proximal segment, and a force sensing mechanism. The force sensing mechanism comprises a proximal housing fixed within the proximal segment, a piezoelectric sensor attached to the proximal housing, the piezoelectric sensor having a first portion fixedly attached to the proximal housing and a second portion not fixedly attached to the proximal housing, and a distal housing fixed within the distal segment, the distal housing contacting the second portion of the piezoelectric sensor and comprising a protrusion configured to apply an axial force to the second portion of the piezoelectric sensor when an external force is applied to the distal segment.

[0016] In Example 17, in the catheter of Example 16, the proximal housing includes an upper surface, a lower surface, and a cavity extending from the lower surface through the upper surface. The first part of the piezoelectric sensor is fixedly attached to the upper surface, and the second part of the piezoelectric sensor extends at least partially across the cavity.

[0017] In Example 18, in the catheter of Example 17, the proximal housing is disposed within a part of the cavity and includes a compressible backing member that contacts the second part of the piezoelectric sensor on the side opposite to the protrusion on the distal housing. The backing member resists deformation of the second part of the piezoelectric sensor when an external force is applied to the distal segment.

[0018] In Example 19, in the catheter of Example 17, the piezoelectric sensor has an arcuate or rectangular outer shape when viewed in a direction parallel to the longitudinal axis. In Example 20, in the catheter of Example 17, the piezoelectric sensor has an annular shape when viewed in a direction parallel to the longitudinal axis. The first part is the outer peripheral part of the piezoelectric sensor, and the second part is located radially inward of the first part of the piezoelectric sensor.

[0019] In Example 21, in the catheter of Example 17, the piezoelectric sensor is a substantially circular disk, and the second part of each piezoelectric sensor extends across the corresponding cavity. In Example 22, the catheter of Example 1 further includes a preloading mechanism that is operably coupled to the proximal housing and is configured to allow a user to selectively apply a preload to the piezoelectric sensor.

[0020] In Example 23, a catheter adapted to measure a contact force, the catheter comprising a elongate shaft having a proximal end and a distal end, and a distal end portion extending distally from the distal end of the shaft. The distal end portion defines a longitudinal axis extending therethrough and comprises a proximal segment, a distal segment located distal to the proximal segment, and a force sensing mechanism, the force sensing mechanism comprising a proximal housing fixed within the proximal segment, the proximal housing having a bottom surface and a top surface, and a plurality of piezoelectric sensors circumferentially spaced apart from each other about the proximal housing, each piezoelectric sensor having a first portion fixedly attached to the proximal housing and a second portion not fixedly attached to the proximal housing, and a distal housing fixed within the distal segment and including a plurality of protrusions, each of the plurality of protrusions contacting a corresponding second portion of one of the plurality of piezoelectric sensors and configured to apply an axial force to the second portion of the corresponding piezoelectric sensor when an external force is applied to the distal segment, and each of the plurality of piezoelectric sensors is configured to generate an output indicative of the amount of axial force applied to the second portion of the corresponding piezoelectric sensor in response to an external force applied to the distal segment.

[0021] In Example 24, in the catheter of Example 23, the proximal housing includes a plurality of cavities extending from the bottom surface through the top surface, each of the plurality of cavities being aligned with a corresponding one of the plurality of piezoelectric sensors, and the second portion of each of the plurality of piezoelectric sensors extends at least partially across a corresponding one of the plurality of cavities.

[0022] In Example 25, in the catheter of Example 24, the proximal housing includes a compressible backing material disposed within each of the plurality of cavities and contacting the second portion of the piezoelectric sensor disposed above the corresponding protrusion on the distal housing and on the opposite side of the corresponding protrusion, the backing material resisting deformation of the second portion of the piezoelectric sensor when an external force is applied to the distal segment.

[0023] In Example 26, in the catheter of Example 24, each piezoelectric sensor has an annular shape when viewed from a direction parallel to the longitudinal axis, the first portion is the outer radial portion of the piezoelectric sensor, and the second portion is the inner radial portion of the piezoelectric sensor.

[0024] In Example 27, in the catheter of Example 24, each piezoelectric sensor is a substantially circular disk, and the second portion of each piezoelectric sensor extends across the corresponding cavity. In Example 28, in the catheter of Example 24, the force sensing mechanism is attached to the proximal housing and includes three piezoelectric sensors spaced circumferentially about the longitudinal axis, each of the three piezoelectric sensors having a first portion fixedly attached to the proximal housing and a second portion deflectable relative to the first portion, the distal housing including three protrusions, each protrusion contacting a corresponding second portion of one of the three piezoelectric sensors and configured to apply an axial force to the second portion of the corresponding piezoelectric sensor when an external force is applied to the distal segment.

[0025] In Example 29, in the catheter of Example 28, the proximal housing includes three cavities extending from the lower surface through the upper surface, each of the three cavities being aligned with a corresponding one of the three piezoelectric sensors, and the second portion of each of the three piezoelectric sensors extends at least partially across a corresponding one of the three cavities.

[0026] In Example 30, a force sensing mechanism for an ablation catheter, the force sensing mechanism is adapted to measure a contact force, the force sensing mechanism includes a proximal housing having a lower surface and an upper surface, and a plurality of piezoelectric sensors attached to the proximal housing and circumferentially spaced from each other about the proximal housing, each piezoelectric sensor having a first portion fixedly attached to the proximal housing and a second portion not fixedly attached to the proximal housing, a distal housing including a plurality of protrusions, each of the plurality of protrusions contacting a corresponding second portion of the plurality of piezoelectric sensors and configured to apply an axial force to the second portion of the corresponding piezoelectric sensor when an external force is applied to the distal housing, and each of the plurality of piezoelectric sensors is configured to generate an output indicative of the amount of axial force applied to the second portion of the corresponding piezoelectric sensor in response to the external force applied to the distal housing.

[0027] In Example 31, in the force sensing mechanism of Example 30, the proximal housing includes a plurality of cavities extending from the lower surface through the upper surface, each of the plurality of cavities being aligned with a corresponding one of the plurality of piezoelectric sensors, and the second portion of each of the plurality of piezoelectric sensors extends at least partially across a corresponding one of the plurality of cavities.

[0028] In Example 32, in the force sensing mechanism of Example 31, the proximal housing includes a compressible backing material disposed within each of the plurality of cavities and contacting the second portion of the piezoelectric sensor disposed above the corresponding protrusion on the distal housing and opposite the corresponding protrusion, the backing material resisting deformation of the second portion of the piezoelectric sensor when an external force is applied to the distal segment.

[0029] In Example 33, in the force sensing mechanism of Example 30, each piezoelectric sensor has a rectangular shape. In Example 34, in the force sensing mechanism of Example 30, each piezoelectric sensor has an annular shape, the first part is the outer peripheral part of the piezoelectric sensor, and the second part is located radially inside the first part of the piezoelectric sensor.

[0030] In Example 35, in the force sensing mechanism of Example 30, each piezoelectric sensor is a substantially circular disk, and the second part of each piezoelectric sensor extends across the corresponding cavity. Although multiple embodiments are disclosed, further other embodiments of the present invention will become apparent to those skilled in the art from the following detailed description showing and describing exemplary embodiments of the present invention. Therefore, the drawings and the detailed description should be regarded as being essentially exemplary and not restrictive.

Brief Description of the Drawings

[0031]

Fig. 1A - 1C

Fig. 2

Fig. 3

Fig. 4A

Fig. 4B

Fig. 4C

Fig. 5A

Fig. 5B

Fig. 5C

Fig. 6A

Fig. 6B

Fig. 6C

Fig. 6D

Fig. 7A

Fig. 7B

[0032] While the present invention is susceptible to various modifications and alternative forms, specific embodiments have been shown by way of example in the drawings and will be described in detail below. However, the intention is not to limit the present invention to the particular embodiments described. On the contrary, the present invention is intended to cover all modifications, equivalents, and alternative forms included within the scope of the present invention as defined by the appended claims.

[0033] Various cardiac abnormalities can result from inappropriate electrical activity in the heart tissue. Such inappropriate electrical activity includes, but is not limited to, the generation of electrical signals, the conduction of electrical signals, and / or the mechanical contraction of tissue in a way that does not support efficient and / or effective cardiac function. For example, regions of heart tissue may become electrically activated early or otherwise out of sync during the cardiac cycle, causing the heart cells in that region and / or adjacent regions to contract arrhythmically. As a result, abnormal cardiac contractions occur that are not timed to optimal cardiac output. In some cases, a region of heart tissue can result in a defective electrical pathway (e.g., a short circuit) that causes an arrhythmia such as atrial fibrillation or supraventricular tachycardia. In some cases, inactivated tissue (e.g., scar tissue) may be preferable to dysfunctional heart tissue.

[0034] Cardiac ablation is a procedure that treats heart tissue to inactivate the tissue. The tissue to be ablated can be associated with inappropriate electrical activity, as described above. Cardiac ablation can form ablation lesions in the tissue to prevent the tissue from inappropriately generating or conducting electrical signals. For example, the formation of ablation lesions in lines, circles, or other heart tissue can block the propagation of errant electrical signals. In some cases, cardiac ablation is intended to cause necrosis of the heart tissue and for scar tissue to reform over the ablation lesion so that the scar tissue is not associated with inappropriate electrical activity. Ablation lesion formation therapies include, among others, electrical ablation, radiofrequency ablation, cryoablation, microwave ablation, laser ablation, and surgical ablation. Although cardiac ablation therapy is referred to as an example herein, various embodiments of the present disclosure can be directed to catheters that deliver ablation and / or non-ablation diagnostics and / or other treatments for other types of tissue.

[0035] Ideally, ablation therapy can be performed in a minimally invasive manner, such as using a catheter introduced into the heart through a blood vessel, rather than surgically opening the heart for direct access (such as in a maze surgical procedure). For example, a single catheter can be used to electrophysiologically examine the inner surface of the heart and identify electrical activation patterns. From these patterns, a clinician can identify regions of inappropriate electrical activity and ablate the heart tissue to kill or isolate the tissue associated with the inappropriate electrical activity. However, since direct access is not possible with catheter-based procedures, a clinician may need to interact only with the heart tissue through a single catheter and keep track of all the information collected by the catheter or otherwise related to the procedure. In particular, it can be difficult to determine the location of the treatment element (e.g., proximity to the tissue), the quality of the ablation lesion, and whether the tissue has formed a complete ablation lesion, an inadequate ablation lesion (e.g., still capable of generating and / or conducting unwanted electrical signals), or an excessive ablation lesion (e.g., cutting through the heart wall or otherwise weakening it). The quality of the ablation lesion can depend on the degree of contact between the ablation element and the target tissue. For example, an ablation element that barely touches the tissue may not be properly positioned for effective ablation therapy. Conversely, pressing the ablation element too strongly against the tissue can result in too much ablation energy or cause perforation.

[0036] The present disclosure relates, among other things, to methods, devices, and systems for assessing the degree of contact between a portion of a catheter (e.g., an ablation element) and tissue. Understanding the degree of contact, such as the magnitude and direction of the force generated by the contact between the catheter and the tissue, can be useful for determining the extent of ablation lesion formation in the target tissue. Information regarding the extent of ablation lesion formation in cardiac tissue can be used, in particular, to determine whether the tissue should be further ablated or whether the tissue has been successfully ablated. Additionally, or alternatively, the contact indicator can be useful when navigating the catheter, because as the catheter advances within the patient, the user may not feel the force exerted by the tissue on the catheter, which can result in damage or perforation of blood vessels or cardiac tissue.

[0037] Figures 1A - 1C illustrate one embodiment of a system 100 for sensing data from within the body and / or providing therapy. For example, system 100 can be configured to map and / or ablate cardiac tissue, among other options. System 100 includes a catheter 110 connected to a control unit 120 via a handle 114. Catheter 110 can comprise an elongate tubular member having a proximal end 115 connected to the handle 114 and a distal end 116 configured to be introduced into the left atrium of the heart 101 or other regions of the body. As shown in Figure 1A, the distal end 116 of catheter 110 is within the left atrium of the heart 101.

[0038] As shown in FIG. 1B, the distal end 116 of the catheter 110 includes a proximal segment 111, a force sensing mechanism 112, and a distal segment 113. The proximal segment 111 and the distal segment 113 can be coaxially aligned with each other in a reference direction as shown in FIG. 1B, and the force sensing mechanism 112 bridges the proximal segment 111 and the distal segment 113. Specifically, in the illustrated embodiment, each of the proximal segment 111 and the distal segment 113 is coaxially aligned with a common longitudinal axis 109. In one embodiment, the longitudinal axis 109 can extend through the respective radial centers of the proximal segment 111 and the distal segment 113 and can extend through the radial center of the distal end 116 as a whole. In some embodiments, the coaxial alignment of the proximal segment 111 with the distal segment 113 can correspond to the reference direction. As shown, the distal end 116 extends linearly at least along the proximal segment 111 and the distal segment 113. In some embodiments, this linear arrangement of the proximal segment 111 and the distal segment 113 can correspond to the reference direction.

[0039] The distal segment 113 or any other segment can be in the form of an electrode configured to sense electrical activity such as an electrical cardiac signal. In other embodiments, such an electrode can be additionally or alternatively used to deliver ablation energy to tissue.

[0040] In various embodiments, the force sensing mechanism 112 provides a force sensing function to the catheter 110. For example, as shown in FIGS. 1B and 1C, the catheter 110 is configured to sense the force exerted on the distal segment 113 by the engagement of the distal segment 113 with the tissue 117 of the heart 101. In various embodiments, the distal segment 113 may be relatively rigid such that when the distal segment 113 engages the tissue 117, the force applied to the tissue 117 by the tip of the distal segment 113 can be transmitted to the proximal segment 111, and the magnitude of the applied force, and in some embodiments, the direction of the applied force, can be sensed by the force sensing mechanism 112. As shown in FIGS. 1B and 1C, the force applied from the tissue causes a relative displacement between the proximal segment 111 and the distal segment 113 (one of ordinary skill in the art will recognize that this relative displacement, which can be on the order of a few micrometers, is shown greatly exaggerated in FIG. 1C for illustrative purposes). One or more sensors within the distal end 116 of the catheter 110 sense the degree of flexion or axial movement of the distal segment 113 relative to the proximal segment 111, as further described herein, to determine the magnitude of the applied force, and in some embodiments, the direction of the applied force. When the distal segment 113 is no longer engaged with the tissue 117, the proximal segment 111 and the distal segment 113 return to the reference direction shown in FIG. 1B.

[0041] The control unit 120 of the system 100 includes a display 121 (e.g., a liquid crystal display or a cathode ray tube) for displaying information. The control unit 120 further includes a user input section 122 that can include one or more buttons, toggles, trackballs, mice, touch pads, etc. for receiving user input. The user input section 122 can alternatively or additionally be disposed on the handle 114. The control unit 120 can include a control circuit for performing the functions referred to herein. Part or all of the control circuit can alternatively be located within the handle 114.

[0042] FIG. 2 shows a block diagram illustrating an example of a control circuit capable of performing the functions referred to in this specification. This control circuit or other control circuits can be housed within control unit 120, which can comprise a single housing or multiple housings with components distributed among the multiple housings. The control circuit can additionally or alternatively be housed within handle 114. The components of control unit 120 can be powered by a power source (not shown) capable of supplying power to any of the components of control unit 120 and system 100, as is known in the art. The power source can, among several options, be plugged into an electrical outlet and / or be powered by a battery.

[0043] Control unit 120 can include a catheter interface 123. Catheter interface 123 can include a plug for receiving a cord from handle 114. Catheter 110 can include, between its distal end 116 and proximal end 115, a plurality of conductors (not shown but known in the art) for transmitting electrical signals to catheter interface 123. Through catheter interface 123, control unit 120 (and / or handle 114 if the control circuit is included therein) can send electrical signals to and / or receive electrical signals from any element within catheter 110. Catheter interface 123 can transmit signals to any of the components of control unit 120.

[0044] The control unit 120 can include hardware and software for use in imaging the tissue being mapped and / or treated. For example, in one embodiment, the control unit 120 can include an ultrasonic subsystem 124 that includes components for operating the ultrasonic functionality of the system 100. The illustrated example of the control circuit shown in FIG. 2 includes the ultrasonic subsystem 124, but it should be understood that not all embodiments will include the ultrasonic subsystem 124 or any circuitry for imaging the tissue. The ultrasonic subsystem 124 can include a signal generator configured to generate signals for ultrasonic transmission, and a signal processing component (e.g., a high pass filter) configured to filter and process reflected ultrasonic signals received by the ultrasonic sensor in sensing mode and transmitted through conductors within the catheter 110 to the ultrasonic subsystem 124. The ultrasonic subsystem 124 can transmit signals to elements within the catheter 110 via the catheter interface 123 and / or receive signals from elements within the catheter 110 via the catheter interface 123.

[0045] However, it is emphasized that the ultrasonic subsystem 124 or other types of imaging subsystems are strictly optional and need not be included in the control unit 120. The control unit 120 can include an ablation subsystem 125. The ablation subsystem 125 can include components for operating the ablation function of the system 100. The illustrated example of the control circuit shown in FIG. 2 includes an ablation subsystem, but it should be understood that not all embodiments include the ablation subsystem 125 or any circuit for generating an ablation treatment. The ablation subsystem 125 can include an ablation generator that provides different treatment outputs depending on a particular configuration. In one embodiment, the ablation generator is configured to generate a high-frequency alternating current signal for supplying high-frequency ablation energy to one or more electrodes. Alternatively, the ablation subsystem 125 and corresponding ablation generator can be configured to provide a relatively high voltage pulse (single-phase or two-phase) to achieve pulsed-field ablation, thereby generating a desired ablation lesion in the target tissue via irreversible electroporation. The ablation subsystem 125 can support any other type of ablation treatment, such as microwave ablation. The ablation subsystem 125 can deliver a signal or other type of ablation energy to the catheter 110 through the catheter interface 123.

[0046] The control unit 120 can include a force sensing subsystem 126. The force sensing subsystem 126 can include components for measuring the force received by the catheter 110. Such components can include a signal processor, an analog-to-digital converter, an operational amplifier, a comparator, and / or any other circuit for conditioning and measuring one or more signals. The force sensing subsystem 126 can supply current to a sensor, such as a piezoelectric sensor (described below with reference to FIGS. 3-7B) within the catheter 110, through the catheter interface 123, and receive a signal from the sensor within the catheter 110 through the catheter interface 123.

[0047] Each of the ultrasonic subsystem 124 (if present), the ablation subsystem 125, and the force sensing subsystem 126 can send signals to and receive signals from the processor 127. The processor 127 can be any type of processor for performing computer functions. For example, the processor 127 can execute program instructions stored in the memory 128 to perform any of the functions referred to herein, such as determining the magnitude and direction of the force received by the catheter 110.

[0048] The control unit 120 further includes an input / output subsystem 129 that can support user input and output functions. For example, the input / output subsystem 129 can support the display 121 to display any of the information referred to herein, such as, among other options, tissue, the catheter 110, and a graphical representation of the magnitude and direction of the force received by the catheter 110. The input / output subsystem 129 can log keys and / or other input entries via the user input section 122 and route the entries to other circuits.

[0049] A single processor 127 or multiple processors can execute the functions of one or more subsystems, and such subsystems can share control circuitry. Although different subsystems are presented herein, the circuitry can be divided among more or fewer subsystems that can be housed separately or together. In various embodiments, the circuitry is not distributed among the subsystems, but rather is provided as a unified computing system. Whether distributed or integrated, the components can be electrically connected to coordinate and share resources to perform functions.

[0050] FIG. 3 is a perspective view of the distal portion of a cardiac ablation catheter 300. In an embodiment, the cardiac ablation catheter 300 corresponds to the ablation catheter 110 shown in FIG. 1 and includes a distal assembly 302. As shown, the distal assembly 302 is disposed axially along a longitudinal axis 303 defined by a shaft (not shown in FIG. 2) of the ablation catheter 300. The distal assembly 302 includes a proximal segment 304, a distal segment 305, and a force sensing mechanism 306. The distal assembly 302 further includes a tip electrode 312 and a ring electrode 314, the tip electrode 312 is disposed at the distal end of the distal assembly 302, and the ring electrode 314 is disposed proximal to the tip electrode 312 and spaced apart from the tip electrode 312. In an embodiment, the distal assembly 302 may include additional electrodes, such as electrodes 316, 318 disposed proximal to and longitudinally spaced from the electrodes 312 and 314. In other embodiments within the scope of the present disclosure, more or fewer electrodes may be employed.

[0051] The specific operations of the various electrodes (or electrode pairs) can vary depending on the specific clinical use of the ablation catheter 300. In embodiments, the electrodes 312, 314, 316, and 318 can be configured to operate as ablation electrodes, sensing electrodes, or both. For example, any or all of the electrodes 312, 314, 316, and 318 can be configured to be operable for delivering ablation energy to target tissue. Additionally, or alternatively, any or all of the electrodes 312, 314, 316, and 318 can be operable as sensing electrodes configured to sense electrical signals (e.g., electric fields generated by an injected current for use in, for example, sensing endogenous cardiac activation signals and / or impedance-based location tracking, tissue proximity or contact). In one embodiment, the electrodes 312, 314 can be configured to operate as ablation electrodes for supplying bipolar ablation energy, particularly pulsed field ablation energy for local ablation of cardiac tissue. In embodiments, the electrodes 316, 318 can be operable as sensing electrodes or, alternatively, as ablation electrodes. In some cases, the electrodes 316, 318 can be configured to measure local impedance and function as position sensors for sensing the local electric field in five degrees of freedom (e.g., five different movements, i.e., x, y, z, acceleration, and rotation). In embodiments, except as specifically described herein, the electrodes 312, 314, 316, and 318 can be configured according to the content described in U.S. Patent Application No. 63 / 194,716, filed by the same applicant and co-pending, which is hereby incorporated by reference in its entirety.

[0052] However, it is emphasized that the present disclosure is not limited to the specific electrode configuration and number of electrodes shown in FIG. 3. Rather, those skilled in the art will understand that additional variations in electrode configuration, number of electrodes, etc. can be employed within the scope of the present disclosure.

[0053] In an embodiment, the distal assembly 302 further includes an insulating material 330 that encapsulates and forms an insulating surface outside the proximal segment 304 and the distal segment 305. In an embodiment, the insulating material 330 is formed by an overmolding process. Alternatively, the insulating material 330 can be formed using a reflow process in which one or more tubular segments of the insulating material are placed around the distal assembly 302 that is partially assembled and then heated, as is known in the art. In an embodiment, by using an overmolding process to provide the insulating material 330, certain advantages can be obtained, such as reducing or completely eliminating the need for subsequent processing (such as completing the assembly process and injecting a medical adhesive to provide a fluid-tight connection between various components). The insulating material can be commercially available Pebax® 55D and Pelathane® 55D. Both materials are used in the overmolding process and can be adhered to an "epoxy-adherable" wire insulator. Pellethane can be adhered to the tip insulator using a primer (e.g., Sivate® E610) and plasma. Pebax can be adhered to the tip insulator using an adhesive (e.g., Thermedics 1-MP) without plasma.

[0054] As will be understood by those skilled in the art, although not shown in FIG. 3, in various embodiments, ablation catheter 300 may include additional components to enable its functionality. As an example, in embodiments where ablation catheter 300 is of a deflectable or steerable type, ablation catheter 300 may include a structure for effecting controlled deflection of the distal portion of ablation catheter 300 by the user, such as steering wires and associated anchor(s). Additionally, ablation catheter 300 includes conductors disposed within the catheter shaft to electrically couple electrodes 312, 314, 316, and 318, piezoelectric sensors 340, 342, 344, and other electrical components (e.g., magnetic navigation sensor(s) if present) to the associated functional components of system 100. Generally, construction techniques and structures for implementing steerability or deflectability for an ablation catheter and for electrically coupling electrical components to a control unit of an ablation system are well known, and thus those skilled in the art will recognize that a wide range of such techniques may be employed for ablation catheter 300.

[0055] In various embodiments, proximal segment 304 and distal segment 305 are spaced apart from each other such that a small deflection of distal segment 305 relative to proximal segment 304 is enabled when an external force is applied to distal segment 305 by patient tissue, it being understood that such movement may be extremely small (e.g., on the order of a few micrometers). Force sensing mechanism 306 is operably connected to both proximal segment 304 and distal segment 305 and includes a plurality of piezoelectric sensors 340, 342, 344 circumferentially spaced apart from each other about longitudinal axis 303 in the illustrated embodiment. Sensors 340, 342, 344 are configured to generate a variable output based on the force applied to the target tissue by distal segment 305, and the output is adjusted to indicate the magnitude of such force.

[0056] In the embodiment of FIG. 3, the three piezoelectric sensors 340, 342, 344 are present at azimuthal angles evenly spaced about the longitudinal axis 303 (arranged circumferentially evenly about the longitudinal axis 303) and are at the same radial distance from the longitudinal axis 303. When the force exerted on the distal segment 305 of the catheter 300 is coaxial with the longitudinal axis 303, the output from each of the piezoelectric sensors 340, 342, 344 is substantially equal. Based on these equal changes, the control circuit can calculate the magnitude of the force exerted on the distal segment 306. The control circuit can also determine that the force is coaxial with the longitudinal axis 303 since the output is the same for each of the three piezoelectric sensors 340, 342, 344.

[0057] When the force is not coaxial with the longitudinal axis 303, the output of each of the piezoelectric sensors 340, 342, 344 is not equal. Based on this, the magnitude and direction of the force (e.g., unit vector) can be determined by the control circuit.

[0058] Once assembled, the catheter 300 can undergo a calibration step either at the factory or immediately prior to use by a physician. In such a step, a plurality of forces of known magnitude and direction are applied in sequence to the distal segment 306, and the outputs of the piezoelectric sensors 340, 342, 344 can be calibrated based on the known magnitude and direction of the applied forces.

[0059] The magnitude can be expressed in grams or another measure of force. The magnitude can be represented as a dynamic line graph, bar graph, or graphic symbol whose color or intensity changes, and these move over time while indicating new up-to-date force values. The direction can be represented as a unit vector within a three-dimensional reference frame (e.g., with respect to a coordinate system of the X, Y, and Z axes). In some embodiments, a three-dimensional mapping function can be used to track the three-dimensional position of the distal end of the catheter 300 in the three-dimensional reference frame. The magnetic field is generated outside the patient and is sensed by a sensor (not shown) sensitive to the magnetic field within the distal end of the catheter 300 to determine the three-dimensional position and particular orientation of the distal end of the catheter 300 in the three-dimensional reference frame. The direction can be represented with respect to the distal end of the catheter 300. For example, a line directed toward or protruding from the distal segment 306 can represent the direction of the force with respect to the distal segment 306. Similarly, a graphic symbol whose color and / or intensity and / or shape changes can be used to represent the magnitude and / or direction of the force. Such a representation can be performed on a display as described herein.

[0060] The magnitude and direction of the force can be utilized for navigation, among other options, by providing an indicator when the catheter contacts the tissue and / or can be used to evaluate tissue ablation by determining the degree of contact between the ablation element and the tissue. In some embodiments, a force of less than 10 grams is not optimal for forming an ablation lesion in the tissue (e.g., because it is too small), while a force exceeding 40 grams is likewise not optimal for forming an ablation lesion in the tissue (e.g., because it is too large). Thus, a range of 10 to 40 grams may be ideal for forming an ablation lesion in the tissue, and the force output during ablation lesion formation can provide feedback to the user to enable the user to stay within this range. Of course, other force ranges may be used that are ideal for ablation lesion formation.

[0061] Figures 4A, 4B, and 4C are, respectively, a perspective view, a front view, and a cross-sectional view of a force sensing mechanism 406 for use with a catheter 110 according to embodiments of the present disclosure. The force sensing mechanism 406 functionally corresponds to the force sensing mechanism 306 described above. In the illustrated embodiment, the force sensing mechanism 406 includes a plurality (in this case, three) of piezoelectric sensors 440, 442, 444, a rigid proximal housing 450, and a rigid distal housing 454. As shown, the piezoelectric sensors 440, 442, 444 are disposed within and attached to the proximal housing 450. In the illustrated embodiment, the piezoelectric sensors 440, 442, 444 have a generally rectangular shape when viewed in a direction parallel to the axis of the catheter, although other embodiments utilize piezoelectric sensors having different shapes or form factors.

[0062] In various embodiments, the proximal housing 450 is fixedly attached to the proximal segment (111 in FIG. 1, 304 in FIG. 3), and the distal housing 454 is fixedly attached to the distal segment (113 in FIG. 1, 306 in FIG. 3) of the catheters 110, 300 described above. Additionally, the proximal housing 450 and the distal housing 454 are separated by a gap 456 that defines the maximum axial movement of the distal segment relative to the proximal segment under the action of an external force when no external force is applied to the distal segment of the individual catheter. Also, in the illustrated embodiment, a lumen 457 extends longitudinally through both the proximal housing 450 and the distal housing 454 and corresponds to the passage of catheter components (e.g., wires, irrigation tubes, and the like) to the distal segment of the catheter.

[0063] Figure 4C is a cross-sectional front view bisecting the force sensing mechanism 406 through the piezoelectric sensor 440. The specific structural details shown in Figure 4C represent the arrangement of the piezoelectric sensors 442, 444. As shown in Figure 4C, the proximal housing has a proximal surface 458, an opposite distal surface 459, an elongate cavity 460, and a distal recess 470 formed in the distal surface 459, the distal recess 470 defining a shoulder 475. Further as shown in Figure 4C, the distal housing 454 has a proximal surface 478 and an opposite distal surface 479 and includes an axially projecting portion 480 extending proximally from the proximal surface 478.

[0064] As shown in Figure 4C, the piezoelectric sensor 440 includes an upper layer 488, a lower layer 490, and a piezoelectric layer 492 disposed between the upper layer 488 and the lower layer 490. The piezoelectric sensor 440 further constitutes a fixed portion 494 and a free portion 496. Further as shown, any backing element 498 is disposed within the elongate cavity 460 adjacent to the lower layer 490. For simplicity of explanation, only the piezoelectric sensor 440 is shown in detail, but it is emphasized that each of the piezoelectric sensors 442 and 444 has the same structure as the piezoelectric sensor 440. In addition, the overall structure of the force sensing mechanism 406 with respect to the positions of the piezoelectric sensors 442, 444 is the same as that shown in Figure 4C, i.e., the cross-sectional front view bisecting the piezoelectric sensors 442, 444 will appear the same as the structure shown in Figure 4C, including the presence of the recess, the elongate cavity, and the projecting portion and the correspondence with the individual piezoelectric sensors.

[0065] The upper layer 488 and the lower layer 490, or at least a portion thereof, are conductive and function as electrode layers during the operation of the piezoelectric sensor 440. Also, the piezoelectric layer 492 includes a piezoelectric material (e.g., a piezoelectric ceramic such as lead zirconate titanate (PZT) or a piezoelectric polymer such as polyvinylidene fluoride (PVDF)). As is recognized in the art of electromechanics, a piezoelectric sensor generates measurable electrical properties when subjected to mechanical stress.

[0066] It is emphasized that the specific, e.g., three-layer structure of the piezoelectric sensor 440 shown in this specification is merely exemplary and is not intended to limit the scope of potential piezoelectric designs suitable for use in the force sensing mechanism 406. For example, in embodiments, the piezoelectric element itself can be a multi-layer structure or a multi-piece structure. Additionally, the upper layer 488 and the lower layer 490 can themselves be formed of a multi-layer or multi-component structure. In embodiments, all or part of the piezoelectric sensors utilized herein can be coated with a protective outer coating and / or an insulating outer coating (e.g., epoxy) or encapsulated within such a coating.

[0067] Referring particularly to FIG. 4C, the piezoelectric sensor 440 is disposed within the distal recess 470 of the proximal housing 450, the fixed portion 494 is disposed on the shoulder 475, and the free portion 496 extends over the elongate cavity 460. As further illustrated, the backing element 498 abuts against the lower layer 490 along the free portion 496 of the piezoelectric sensor 440. Additionally, the axial protrusion 480 of the distal housing 454 is disposed over and bears upon the upper layer 488 within the region of the free portion 496 of the piezoelectric sensor 440. The piezoelectric sensors 442, 444 each have the same positional relationship and each comprise a distal recess, a shoulder, and an elongate cavity within the proximal housing 450 and an axial protrusion within the distal housing 454, as shown in FIG. 4C with respect to the piezoelectric sensor 440. Additionally, in embodiments, the backing element is disposed within the elongate cavity adjacent to the piezoelectric sensors 442, 444 in the same manner as shown in FIG. 4C.

[0068] In an embodiment, the fixed portion 494 of the piezoelectric sensor 440 is firmly attached to the shoulder 475 of the proximal housing 450, and the free portion 496 of the piezoelectric sensor 440 effectively forms a cantilever beam over the longitudinally extending cavity 460. Since the rigid axis protrusion 480 of the distal housing 454 is in direct contact with the upper layer 488 of the piezoelectric sensor 440, the force applied to the distal segment 305 (FIG. 3) of the catheter is transmitted to the free portion 496 of the piezoelectric sensor 440. Additionally, the cantilever beam arrangement of the free portion 496 maximizes the piezoelectric effect exhibited by the piezoelectric sensor 440 in response to the transmitted force (i.e., the stress induced in the piezoelectric layer 492 and the corresponding sensor output resulting from the piezoelectric effect are substantially greater than those of an arrangement where the piezoelectric sensor is firmly fixed along its entire length).

[0069] In an embodiment, the backing element 498, if present, is made of a compressible material (e.g., an elastomer) and provides some support to the free portion 496 of the piezoelectric sensor 440 and functions to resist deformation of the piezoelectric sensor 440 when an external force is applied, but does not rigidly resist all such deformations. In an embodiment, the mechanical properties of the backing element 498 can be adjusted to fine-tune the piezoelectric effect exhibited by the piezoelectric sensor 440.

[0070] As will be understood by those skilled in the art, since the piezoelectric sensor 440 is an electromechanical device, electrical leads (not shown) are attached to the electrode structures on the upper layer 488 and the lower layer 490. In embodiments, the electrical leads may be routed through the elongate cavity 460, and may be routed into the lumen 457 or through some other access feature within the proximal housing 450. As further shown in FIG. 4C, in embodiments, the potting material 499 may be disposed within the open space within the proximal housing 450, and this potting material 499 may function to seal the catheter and the internal components of the force sensing mechanism 406, and may also function to reinforce the structural attachment between the proximal and distal segments of the catheter. In embodiments, the potting material 499 and the backing element 498 may be formed from the same compressible material and may be formed in a single manufacturing process, although this is not strictly required. In some embodiments, the potting material 499 (or some other compressible material) may be disposed within the gap 456. In some embodiments, the backing element 498 and / or the potting material 499 may be completely omitted.

[0071] It is again emphasized that the configuration shown in FIG. 4C with respect to the piezoelectric sensor 440 is representative of the piezoelectric sensors 442 and 444. As is generally recognized in the electromechanical art, piezoelectric sensors 440, 442, 444 exhibit electrical characteristics that vary as a function of the stress generated within their respective piezoelectric layers. In an embodiment, an alternating electrical signal generated by control unit 120 (FIG. 1A) can be delivered to electrodes in the upper and lower layers of each piezoelectric sensor 440, 442, 444, and changes in the response of the electrical response exhibited by the piezoelectric layer within each sensor, caused by fluctuations in the stress generated within the piezoelectric layer by the force transferred through the distal segment of catheter 110, can be measured in comparison to a calibrated value of the magnitude of the force. Exemplary changes in electrical characteristics measured in such embodiments can include resonance frequency, electrical impedance, or decay time constant. In other embodiments, changes in the capacitance of piezoelectric sensors 440, 442, 444 can be measured directly due to changes in the stress induced within the piezoelectric sensors. The latter embodiments eliminate the requirement to supply an excitation signal from control unit 120, but may be less sensitive compared to embodiments that utilize such an excitation signal.

[0072] FIGS. 5A, 5B, and 5C are, respectively, a perspective view, a front view, and a cross-sectional view of a force sensing mechanism 506 for use with catheter 110, according to an embodiment of the present disclosure. Force sensing mechanism 506 functionally corresponds to force sensing mechanism 306 described above. In the illustrated embodiment, force sensing mechanism 506 includes a plurality (in this case, three) of annular piezoelectric sensors 540, 542, 544, a rigid proximal housing 550, and a rigid distal housing 554. As shown, piezoelectric sensors 540, 542, 544 are disposed within and attached to proximal housing 550.

[0073] In various embodiments, the proximal housing 550 is fixedly attached to the proximal segment (111 of FIG. 1, 304 of FIG. 3), and the distal housing 554 is fixedly attached to the distal segment (113 of FIG. 1, 306 of FIG. 3) of the catheters 110, 300 described above. Additionally, the proximal housing 550 and the distal housing 554 are separated by a gap 556 that defines the maximum axial movement of the distal segment relative to the proximal segment under the action of an external force when no external force is applied to the distal segment of the individual catheter. Also, in the illustrated embodiment, the lumen 557 extends longitudinally through both the proximal housing 550 and the distal housing 554 and corresponds to the passage of catheter components (e.g., wires, irrigation tubes, and the like) to the distal segment of the catheter.

[0074] FIG. 5C is a cross-sectional front view bisecting the force sensing mechanism 606 through the piezoelectric sensor 540. The details of the particular structure shown in FIG. 5C represent the arrangement of the piezoelectric sensors 542, 544. As shown in FIG. 5C, the proximal housing has a proximal face 558, an opposite distal face 559, an elongate cavity 560, and a distal recess 570 formed in the distal face 559, and the distal recess 570 defines a shoulder 575. Further, as shown in FIG. 5C, the distal housing 554 has a proximal face 578 and an opposite distal face 579 and includes an axially projecting portion 580 extending proximally from the proximal face 578.

[0075] As shown in FIG. 5C, the piezoelectric sensor 540 includes an upper layer 588, a lower layer 590, and a piezoelectric layer 592 disposed between the upper layer 588 and the lower layer 590. The annular shape of the piezoelectric sensor 540 further forms a fixed portion 594 corresponding to the outer peripheral region of the piezoelectric sensor 540, and a free portion 596 that is radially inward of the fixed portion 594 and corresponds to the inner radial region of the piezoelectric sensor 540. As further shown, the annular shape of the piezoelectric sensor forms an opening 597 that is located substantially at the center through the piezoelectric sensor 540. As further shown, any backing element 598 is disposed in the vertically elongated cavity 560 adjacent to the lower layer 590. For simplicity of explanation, only the piezoelectric sensor 540 is shown in detail, but it is emphasized that each of the piezoelectric sensors 542 and 544 has the same structure as the piezoelectric sensor 540. In addition, the overall structure of the force sensing mechanism 506 with respect to the positions of the piezoelectric sensors 542 and 544 is the same as that shown in FIG. 5C, that is, a cross-sectional view bisecting the piezoelectric sensors 542 and 544 will appear to be the same as the structure shown in FIG. 5C, including the presence of the recess, the vertically elongated cavity, and the protrusion, and the correspondence with the individual piezoelectric sensors.

[0076] The upper layer 588 and the lower layer 590, or at least a part thereof, are conductive and function as electrode layers during the operation of the piezoelectric sensor 540. Also, the piezoelectric layer 592 includes a piezoelectric material (e.g., a piezoelectric ceramic such as lead zirconate titanate (PZT) or a piezoelectric polymer such as polyvinylidene fluoride (PVDF)). As is recognized in electromechanical art, a piezoelectric sensor generates measurable electrical properties when subjected to mechanical stress.

[0077] With particular reference to FIG. 5C, the distal recess 570 is axially aligned with the elongate cavity 560, the piezoelectric sensor 540 is disposed within the distal recess 570 of the proximal housing 550, the fixed portion 594 is disposed on the shoulder 575, and the free portion 596 extends over the elongate cavity 560. Further as shown, the backing element 598 abuts against the lower layer 590 along the free portion 596 of the piezoelectric sensor 540. Additionally, the axial protrusion 580 of the distal housing 554 is disposed over and straddles the opening 597 such that the axial protrusion loads the upper layer 588 within the region of the free portion 596 of the piezoelectric sensor 540. The piezoelectric sensors 542, 544 each have the same positional relationship and each comprise a distal recess, a shoulder, and an elongate cavity within the proximal housing 550 and an axial protrusion on the distal housing 554 as shown in FIG. 5C with respect to the piezoelectric sensor 540. Additionally, in embodiments, any backing element is disposed within the elongate cavity adjacent to each of the piezoelectric sensors 542, 544 in the same manner as shown in FIG. 5C.

[0078] In an embodiment, the fixed portion 594 of the piezoelectric sensor 540 is rigidly attached to the shoulder 575 of the proximal housing 550 and the free portion 596 of the piezoelectric sensor 540 extends over the elongate cavity 560. Since the rigid axial protrusion 580 of the distal housing 554 is in direct contact with the upper layer 588 of the piezoelectric sensor 540, the force applied to the distal segment 305 (FIG. 3) of the catheter is transmitted to the free portion 596 of the piezoelectric sensor 540. Additionally, the arrangement of the free portion 596 extending over the elongate cavity 560 maximizes the piezoelectric effect exhibited by the piezoelectric sensor 540 in response to the transmitted force (i.e., the stress induced within the piezoelectric layer 592 and the corresponding sensor output resulting from the piezoelectric effect are substantially greater than if the piezoelectric sensor were rigidly fixed along its entire length).

[0079] In an embodiment, the backing element 598, if present, is made of a compressible material (e.g., an elastomer) and provides some support to the free portion 596 of the piezoelectric sensor 540 to function to resist deformation of the piezoelectric sensor 540 when an external force is applied, but at the same time does not rigidly resist all such deformations. In an embodiment, the mechanical properties of the backing element 598 can be adjusted to finely tune the piezoelectric effect exhibited by the piezoelectric sensor 540.

[0080] As will be understood by those skilled in the art, since the piezoelectric sensor 540 is an electromechanical device, electrical leads (not shown) are attached to the electrode structures on the upper layer 588 and the lower layer 590. In an embodiment, the electrical leads may be routed through the longitudinally extending cavity 560 and may be routed into the lumen 557 or through some other access feature within the proximal housing 550. As further shown in FIG. 5C, in an embodiment, the potting material 599 may be disposed within the opening 597 as shown and within the open space within the proximal housing 550, and this potting material 599 may function to seal the internal components of the catheter and the force sensing mechanism 506 and also to reinforce the structural attachment between the proximal and distal segments of the catheter. In an embodiment, the potting material 599 and the backing element 598 may be formed from the same compressible material and may be formed in a single manufacturing process, although this is not strictly required. In some embodiments, the potting material 599 (or some other compressible material) may be disposed within the gap 556. In some embodiments, the backing element 598 and / or the potting material 599 may be completely omitted.

[0081] It is again emphasized that the arrangement shown in FIG. 5C with respect to the piezoelectric sensor 540 is representative of the piezoelectric sensors 542 and 544. In addition, in the embodiments, the piezoelectric sensors 540, 544, and 542 can have forms other than the illustrated annular form. In particular, in the embodiments, the piezoelectric sensors 540, 544, and 542 can be configured as substantially circular disks without a central opening, and the individual free portions are formed by the central portion of the disk disposed over the corresponding longitudinally extending cavity.

[0082] Figures 6A-6D illustrate an alternative force sensing mechanism 606 for use with the catheter 110 according to embodiments of the present disclosure. Figures 6A and 6B are exploded perspective views of the force sensing mechanism 606. Figure 6C is a front view of the force sensing mechanism 606, and Figure 6D is a cross-sectional front view of the force sensing mechanism 606 taken along line 6D-6D of Figure 6C.

[0083] The force sensing mechanism 606 functionally corresponds to the force sensing mechanism 306 described above. In the illustrated embodiment, the force sensing mechanism 606 includes a single annular piezoelectric sensor 640, a rigid proximal housing 650, and a rigid distal housing 654. As illustrated, the piezoelectric sensor 640 is disposed within and attached to the proximal housing 650.

[0084] In various embodiments, the proximal housing 650 is fixedly attached to the proximal segment (111 of FIG. 1, 304 of FIG. 3), and the distal housing 654 is fixedly attached to the distal segment (113 of FIG. 1, 306 of FIG. 3) of the catheters 110, 300 described above. In addition, the proximal housing 650 and the distal housing 654 are separated by a gap 656 that defines the maximum axial movement of the distal segment relative to the proximal segment under an external force when no external force is applied to the distal segment of the individual catheter. Also, in the illustrated embodiment, a lumen 657 extends longitudinally through both the proximal housing 650 and the distal housing 654 and corresponds to the passage of catheter components (e.g., wires, irrigation tubes, and the like) to the distal segment of the catheter.

[0085] As shown, the proximal housing 650 has a proximal surface 658, an opposite distal surface 659, and a distal recess 670 formed in the distal surface 659. As seen in the cross-sectional view of FIG. 6C, the distal recess 670 defines a shoulder 675. Additionally, the distal housing 654 has a proximal surface 678, an opposite distal surface 679, and an annular axially projecting portion 680 extending proximally from the proximal surface 678.

[0086] As shown in FIG. 6C, the piezoelectric sensor 640 includes an upper layer 688, a lower layer 690, and a piezoelectric layer 692 disposed between the upper layer 688 and the lower layer 690. The annular shape of the piezoelectric sensor 640 further forms a fixed portion 694 corresponding to the outer peripheral region of the piezoelectric sensor 640, and a free portion 696 that is radially inward of the fixed portion 694 and corresponds to the inner radial region of the piezoelectric sensor 640. As further shown, any backing element 698 is disposed within the recess 670 adjacent to the lower layer 690.

[0087] The upper layer 688 and the lower layer 690, or at least a portion thereof, are conductive and function as electrode layers during the operation of the piezoelectric sensor 640. Also, the piezoelectric layer 692 includes a piezoelectric material (e.g., a piezoelectric ceramic such as lead zirconate titanate (PZT) or a piezoelectric polymer such as polyvinylidene fluoride (PVDF)). As is recognized in electromechanical art, a piezoelectric sensor generates measurable electrical properties when subjected to mechanical stress.

[0088] Referring particularly to FIG. 6C, the piezoelectric sensor 640 is arranged such that the fixed portion 694 is disposed on the shoulder 675 and the free portion 696 extends over the lower part of the recess 670. As further shown, the backing element 698 abuts the lower layer 690 along the free portion 696 of the piezoelectric sensor 640. Additionally, the axially projecting portion 680 of the distal housing 654 is arranged such that the axially projecting portion 680 loads the upper layer 688 within the region of the free portion 696 of the piezoelectric sensor 640.

[0089] In an embodiment, the fixed portion 694 of the piezoelectric sensor 640 is firmly attached to the shoulder 675 of the proximal housing 650, and the free portion 696 of the piezoelectric sensor 640 extends over the recess 670. Since the rigid axis direction protrusion 680 of the distal housing 654 is in direct contact with the upper layer 688 of the piezoelectric sensor 640, the force applied to the distal segment 305 (FIG. 3) of the catheter is transmitted to the free portion 696 of the piezoelectric sensor 640. In addition, the arrangement of the free portion 696 extending over the longitudinally extending cavity 660 maximizes the piezoelectric effect exhibited by the piezoelectric sensor 640 in response to the transmitted force (i.e., the stress induced in the piezoelectric layer 692 and the sensor output resulting from the corresponding piezoelectric effect are substantially greater than those in an arrangement where the piezoelectric sensor is firmly fixed along its entire length).

[0090] In an embodiment, the backing element 698, if present, is made of a compressible material (e.g., an elastomer) and provides some support to the free portion 696 of the piezoelectric sensor 640 and functions to resist deformation of the piezoelectric sensor 640 when an external force is applied, but does not rigidly resist all such deformations. In an embodiment, the mechanical properties of the backing element 698 can be adjusted to finely tune the piezoelectric effect exhibited by the piezoelectric sensor 640.

[0091] As further shown in FIG. 6C, in an embodiment, the potting material 699 can be disposed within the opening 697 as shown and within the open space within the proximal housing 650, and this potting material 699 can function to seal the internal components of the catheter and the force sensing mechanism 606 and also to strengthen the structural attachment between the proximal and distal segments of the catheter. In an embodiment, the potting material 699 and the backing element 698 can be formed from the same compressible material and can be formed in a single manufacturing process, although this is not strictly necessary. In some embodiments, the potting material 699 (or some other compressible material) can be disposed within the gap 656.

[0092] In operation, the annular piezoelectric sensor 640 is configured to operate in the same manner as each of the annular piezoelectric sensors 540, 542, and 544 described elsewhere in this specification. However, since the force sensing mechanism 606 includes only a single piezoelectric sensor, the force sensing mechanism 606 is configured to sense only the magnitude of the applied external force (and not the direction).

[0093] Figures 7A and 7B are, respectively, a front view and a cross-sectional view of an alternative force sensing mechanism 706 for use with the catheter of FIG. 3, according to various embodiments of the present disclosure. The force sensing mechanism 706 is configured in many respects similarly to the force sensing mechanism 606 and includes a single annular piezoelectric sensor 740, a proximal housing 750, and a distal housing 754 separated by a gap 756. The proximal housing 750 includes an annular recess 770, and the piezoelectric sensor 740 is disposed within the annular recess 770 in the same manner as the piezoelectric sensor 640, together with a fixed portion 794 and a free portion 796. Additionally, the distal housing 754 includes an annular axial protrusion 780 that applies a load to the free portion 796 of the piezoelectric sensor 740 in the same manner as described above in connection with various other embodiments. The illustrated embodiment further includes a backing element 798 that supports the free portion 796 of the piezoelectric sensor 740, but in other embodiments, this backing element 798 may be omitted.

[0094] The force sensing mechanism 706 differs from the previous embodiment in that it further includes a semi-circular preload collar 720 operatively coupled to the proximal housing 750 and the distal housing 754. The preload collar 720 is configured to apply an initial load to the piezoelectric sensor 740 and to apply a corresponding stress to the piezoelectric sensor 740, or alternatively, to facilitate the assembly of the force sensing mechanism 706 by ensuring close contact between the annular axial protrusion 780 and the piezoelectric sensor 740.

[0095] The preload collar 720 has a generally semi-circular shape corresponding to the shapes of the proximal housing 750 and the distal housing 754. As shown, the preload collar 720 has a distal body portion 722 having an upper surface 724 and a lower surface 726, and a shank portion 730 extending proximally from the lower surface 726.

[0096] As further shown, in the embodiments of FIGS. 7A-7B, the distal housing 754 has an annular slot 732 extending radially inwardly around the circumference of the distal housing 754, and the annular slot 732 is generally rectangular in shape so as to complement the cross-sectional shape of the distal body portion 722 of the preload collar 720. The annular slot 732 forms a radially bearing surface 734 adjacent to the lower surface 726 of the distal body portion 722 of the preload collar 720. Additionally, an annular wall 736 is formed on the outer periphery of the proximal housing 750 radially outside the recess 770.

[0097] In an embodiment, the outer surface of the shank portion 730 is rotatably engaged with the inner surface of the annular wall 736 at the connection portion 738 (FIG. 7B). The connection portion 738 schematically shown in FIG. 7B is configured such that rotation of the preload collar 720 relative to the distal housing 754 axially moves the preload collar 720 relative to the proximal housing 740 and the distal housing 754. In one exemplary embodiment, the connection portion 738 can be configured as a threaded connection portion having a female thread and a male thread that engage the annular wall 736 and the shank portion 720, respectively.

[0098] FIG. 7B shows the force sensing mechanism 706 in a substantially unloaded state, in which the protrusion 780 is in contact with the piezoelectric sensor 740 but applying minimal or no force, and the lower surface 726 of the body portion 722 of the preload collar 720 is axially spaced from the radial bearing surface 734 of the distal housing 754. As will be appreciated by those skilled in the art, from the illustrated state, due to the configuration of the connection portion 738, selective rotation of the preload collar 720 relative to the proximal housing 720 causes the preload collar 720 to translate axially such that the lower surface 726 of the body portion 722 of the preload collar 720 contacts the radial bearing surface 734 of the distal housing 734. When the lower surface 726 of the body portion 722 of the preload collar 720 contacts the radial bearing surface 734 of the distal housing 754, further rotation of the preload collar 720 in the same direction biases the distal housing 754 towards the proximal housing 750 and the annular protrusion 780 applies a force to the free portion 796 of the piezoelectric sensor 740. In this way, during assembly of the force sensing mechanism 706, the preload collar 720 can be manipulated to confirm the necessary contact between the protrusion 780 and the piezoelectric sensor 740 and, if necessary, apply a selective preload to effect adjustment of the piezoelectric sensor 740.

[0099] The various embodiments of the present disclosure represent significant improvements over conventional catheter force sensing techniques. In particular, the embodiments described herein eliminate the need for complex spring mechanisms utilized in prior art catheters. Similarly, the piezoelectric sensors of the various embodiments are relatively low cost compared to inductive position sensors utilized in prior art catheters.

[0100] Various changes and additions can be made to the exemplary embodiments described without departing from the scope of the invention. For example, while the above-described embodiments refer to specific features, the scope of the invention includes embodiments having different combinations of features and embodiments that do not include all of the described features. Accordingly, the scope of the invention is intended to embrace all such alternatives, modifications, and variations, together with all of their equivalents, as are included within the scope of the claims.

Claims

**Claim 1** A catheter adapted to measure a contact force, comprising: an elongate shaft having a proximal end and a distal end; a distal end portion extending distally from the distal end of the shaft, the distal end portion defining a longitudinal axis extending therethrough, the distal end portion comprising: a proximal segment; a distal segment located distal to the proximal segment, the distal segment being spaced apart from the proximal segment with a gap therebetween; a force sensing mechanism, the force sensing mechanism comprising: a proximal housing fixed within the proximal segment; a piezoelectric sensor attached to the proximal housing, the piezoelectric sensor having a first portion fixedly attached to the proximal housing and a second portion not fixedly attached to the proximal housing; a distal housing fixed within the distal segment, the distal housing contacting the second portion of the piezoelectric sensor and including a protrusion configured to apply an axial force to the second portion of the piezoelectric sensor when an external force is applied to the distal segment; and the piezoelectric sensor is configured to generate an output indicative of the amount of axial force applied to the second portion of the piezoelectric sensor in response to an external force applied to the distal segment. **Claim 2** The catheter according to claim 1, wherein the proximal housing includes an upper surface, a lower surface, and a cavity extending proximally from the upper surface, the first portion of the piezoelectric sensor being fixedly attached to the upper surface, and the second portion of the piezoelectric sensor extending at least partially across the cavity. **Claim 3** The catheter according to claim 2, wherein the piezoelectric sensor has an arcuate or rectangular outer shape when viewed in a direction parallel to the longitudinal axis. **Claim 4** The catheter according to claim 2, wherein the piezoelectric sensor has an annular shape when viewed in a direction parallel to the longitudinal axis, the first portion being an outer peripheral portion of the piezoelectric sensor, and the second portion being located radially inward of the first portion of the piezoelectric sensor. **Claim 5** The catheter according to claim 2, wherein the piezoelectric sensor is a substantially circular disk, and the second portion extends across the cavity. **Claim 6** The proximal housing is disposed within a portion of the cavity and includes a compressible backing material that contacts the second portion of the piezoelectric sensor on a side opposite the protrusion on the distal housing. The backing material resists deformation of the second portion of the piezoelectric sensor when an external force is applied to the distal segment. The catheter according to any one of claims 1 to 5.

7. The force sensing mechanism is attached to the proximal housing and includes three piezoelectric sensors spaced circumferentially about the longitudinal axis. Each of the three piezoelectric sensors has a first portion fixedly attached to the proximal housing and a second portion deflectable relative to the first portion. The catheter according to any one of claims 1 to 6.

8. The distal housing includes three protrusions, each of which contacts a corresponding one of the second portions of the three piezoelectric sensors and is configured to apply an axial force to the second portion of the corresponding piezoelectric sensor when an external force is applied to the distal segment. The catheter according to claim 7.

9. Each of the three piezoelectric sensors is configured to generate an output indicative of the amount of axial force applied to the second portion of the piezoelectric sensor in response to an external force applied to the distal segment. The catheter according to claim 8.

10. The proximal housing includes three cavities extending proximally from an upper surface, each of the three cavities being aligned with a corresponding one of the three piezoelectric sensors. The second portion of each of the three piezoelectric sensors extends at least partially across a corresponding one of the three cavities. The catheter according to claim 9.

11. Each piezoelectric sensor has an arcuate or rectangular outer shape when viewed in a direction parallel to the longitudinal axis. The catheter according to claim 10.

12. Each piezoelectric sensor has an annular shape when viewed in a direction parallel to the longitudinal axis. The first portion is an outer peripheral portion of the piezoelectric sensor, and the second portion is located radially inward of the first portion of the piezoelectric sensor. The catheter according to claim 10.

13. Each piezoelectric sensor is a substantially circular disk, and the second portion of each piezoelectric sensor extends across the corresponding cavity, the catheter according to claim 10.

14. A compressible backing material is disposed within a portion of each cavity and contacts the second portion of the corresponding piezoelectric sensor on the side opposite the corresponding protrusion on the distal housing, the backing material resisting deformation of the second portion of the corresponding piezoelectric sensor when an external force is applied to the distal segment, the catheter according to any one of claims 8 to 13.

15. The catheter according to claim 1, further comprising a preloading mechanism operably coupled to the proximal housing and configured to enable a user to selectively apply a preload to the piezoelectric sensor.

Images