Identifying pulmonary vein occlusion by scaling of balloon catheters

Abstract

The present invention is entitled "Identifying Pulmonary Vein Occlusion by Dimensional Deformation of a Balloon Catheter." The present invention discloses a method comprising receiving a position signal indicating the position of a plurality of electrodes disposed on an inflatable balloon mounted at a distal end of a shaft for engaging a lumen of an organ to thereby occlude the lumen. Based on the received position signal, a change in one or more dimensions of the balloon between (i) a first configuration in which the balloon is inflated but not engaged in the lumen and (ii) a second configuration in which the balloon is inflated and engaged in the lumen is calculated. Using the calculated change, the degree to which the balloon occludes the lumen is estimated. The estimated degree of occlusion is presented to a user.

Description

Technical Field

[0001] The present invention relates generally to tracking medical probes within a living body, and particularly to tracking the shape of a medical probe. Background Art

[0002] Inflatable probes for occluding lumens within the body have been previously proposed in the patent literature. For example, U.S. Patent 5,795,325 describes measuring pressure across an occlusion balloon to determine when the pressure on the balloon may cause it to deflect. An alarm indicates when the pressure on the balloon exceeds a predetermined threshold. In another aspect of this invention, when inflating the occlusion balloon, a pressure monitor determines when the rate of increase in pressure relative to the volume of fluid in the balloon reaches a predetermined threshold. A predetermined amount of fluid is then added to the balloon so that the balloon is neither under-inflated nor over-inflated.

[0003] As another example, U.S. Patent Application Publication No. 2011 / 0184400 describes a method and system for cryoablating a large area of tissue within the left atrium. In an exemplary embodiment, a cryotherapeutic device includes a catheter body, a proximal end and a distal end, a first lumen, a second lumen, and an ablation element capable of expanding from a first diameter to a second diameter. The ablation element has a surface portion that conforms to the uneven surface topography of cardiac tissue. The ablation element may include one or more deformable balloons and / or flexible elements. The surface of the balloon may also be shaped by adjusting the pressure within one or more balloons. In addition, because the size, shape, or other dimensions of the blood vessel being occluded may vary, the second balloon may be selectively and controllably expanded to a portion of its total expansion / size tolerance to achieve the desired occlusion. In an exemplary method, a tissue ablation device is provided and utilized to ablate tissue in the left atrium, thereby producing ablation by freezing the tissue. Summary of the Invention

[0004] Embodiments of the present invention provide a method comprising receiving a position signal indicating the position of a plurality of electrodes disposed on an inflatable balloon mounted at a distal end of a shaft for engaging a lumen of an organ to occlude the lumen. Based on the received position signal, a change in one or more dimensions of the balloon between (i) a first configuration in which the balloon is inflated but not engaged within the lumen and (ii) a second configuration in which the balloon is inflated and engaged within the lumen is calculated. Using the calculated change, a degree of occlusion of the lumen by the balloon is estimated. The estimated degree of occlusion is presented to a user.

[0005] In some embodiments, estimating the extent includes deriving a balloon inflation index (BII) from the calculated change in the size, and estimating the extent of occlusion of the lumen by the balloon based on the BII.

[0006] In some embodiments, calculating the change in the dimension includes calculating the change in the radius of the balloon.

[0007] In one embodiment, calculating the change in the radius of the balloon comprises:

[0008] The position of the ablation electrode disposed on the inflatable balloon is measured using effective current position (ACL), the measured position is best fitted to a circle, and the radius of the best-fit circle is calculated.

[0009] In another embodiment, receiving the position signal includes receiving additional position signals from one or more position sensors disposed on the distal end of the shaft, and wherein calculating the change in scale includes calculating a change in the length of the balloon along the longitudinal axis of the balloon based on the additional position signals.

[0010] In some embodiments, estimating the extent to which the balloon occludes the lumen comprises rating the extent numerically. In other embodiments, estimating the extent to which the balloon occludes the lumen comprises rating the extent textually.

[0011] In one embodiment, the lumen comprises the ostium of a pulmonary vein (PV).

[0012] According to an embodiment of the present invention, a system comprising an interface and a processor is also provided. The interface is configured to receive a position signal indicating the position of a plurality of electrodes disposed on an inflatable balloon, the inflatable balloon being mounted at the distal end of a shaft for engaging a lumen of an organ to thereby occlude the lumen. The processor is configured to (a) calculate a change in one or more dimensions of the balloon based on the received position signal, (b) estimate the extent to which the balloon occludes the lumen using the calculated changes in dimensions, and (c) present the estimated degree of occlusion to a user.

[0013] The present invention will be more fully understood through the following detailed description of embodiments of the present invention in conjunction with the accompanying drawings, in which: BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 is a schematic illustration of a catheter-based positioning-tracking and ablation system according to an embodiment of the present invention, the system including a radiofrequency (RF) ablation balloon;

[0015] Figure 2A and Figure 2B are in a free state and a constrained inflated state, respectively, according to an embodiment of the present invention. Figure 1 A schematic side view of a balloon;

[0016] Figure 3 To schematically illustrate the method of deriving the effective current position (ACL) measurement result according to an embodiment of the present invention. Figure 2A and Figure 2B a graphical representation of the change in the radius of the balloon; and

[0017] Figure 4 To schematically illustrate a method for Figure 1 Flowchart of the method and algorithm for estimating the degree of ostial occlusion by balloon. DETAILED DESCRIPTION

[0018] Overview

[0019] In order to effectively ablate luminal tissue using a balloon catheter, such as a radiofrequency (RF) ablation balloon catheter, it is important that the ablation electrodes disposed on the balloon membrane make good physical contact with the tissue being ablated. For example, for safe and effective pulmonary vein (PV) isolation, all ablation electrodes should make good contact around the circumference of the PV's circular ostium. Therefore, it is important to ensure that the balloon completely occludes the vein before performing ablation.

[0020] However, detecting complete occlusion of a lumen such as a rotundum, for example by detecting occlusion of a distal vessel (e.g., a PV vessel), is a procedure that conventionally relies on another modality, such as fluoroscopy. Unfortunately, fluoroscopy (i.e., observing the properties of a radiopaque contrast agent after it has been injected) can sometimes have side effects associated with the use of the contrast agent itself and the X-ray radiation.

[0021] Embodiments of the present invention described below provide improved techniques for monitoring the extent to which an expandable (e.g., inflatable) cardiac ablation balloon occludes a circular lumen (such as the ostium of a PV), for example, immediately prior to ablation. The disclosed techniques provide systems and methods that can provide a physician with an estimated degree of occlusion by estimating the degree to which the balloon occludes the lumen. To derive this estimate, a processor calculates a change in one or more dimensions of the balloon between (i) a first configuration in which the balloon is inflated but not engaged in the lumen and (ii) a second configuration in which the balloon is inflated and engaged in the lumen.

[0022] In some embodiments, estimation of balloon occlusion relies on deriving an estimated degree of balloon inflation using the balloon inflation index (BII) when the balloon is pressed against the wall of the circular lumen.

[0023] In some embodiments, a processor (e.g., a processor of an ablation system) uses the measured change in the radial dimension and / or longitudinal dimension (e.g., radius, length, curvature) of a compressed balloon relative to the same balloon inflated unconstrained to derive a change in the disclosed one or more dimensions, and the BII. By definition, a balloon inflated (i.e., inflated and unconstrained) in free space (such as in the blood pool of a chamber of the heart) has a BII of 100%. A balloon inflated in a constrained space, such as in a lumen (e.g., a pulmonary vein), has a reduced radius while its length increases. The changed scale of the balloon corresponds to a smaller BII, calculated as follows, and the smaller BII provides an indication of the extent to which the circular ostium of the pulmonary vein is occluded.

[0024] In some embodiments, the balloon is first inflated in the blood pool, and the processor measures the dimensions of the inflated balloon in free space to use as a reference (i.e., the dimensions of the inflated and unconstrained balloon are measured). The balloon is then inserted into the PV ostium, and the processor measures the dimensions of the constrained (e.g., compressed) balloon. The processor calculates the BII based on one or more measured changes in the dimensions of the balloon.

[0025] Furthermore, the detection can be performed by (a) comparing the known mechanical shape and dimensions of a fully inflated balloon, e.g., outside the body, with real-time visualization of the deformed balloon prior to ablation, and / or (b) monitoring in real-time rapid changes in balloon shape and dimensions that may result from external forces applied to the balloon by a physician pushing the inflated balloon against the PV ostium to fully occlude the PV.

[0026] In other embodiments, a deflated or partially inflated balloon is first inserted into the lumen, and only then is the balloon inflated to occlude the lumen. In this case, the processor calculates BII using the known dimensions of the free space inflated balloon compared to one or more measured dimensions of the compressed balloon.

[0027] As described above, BII can be defined by various changes in the dimensions of the balloon. For example, assuming that the balloon has a radius R0 and a length L0 when freely inflated, and that due to inflation of the balloon within the orifice, the balloon radius decreases by 10% (i.e., ΔR = -0.1R0), and at the same time the balloon stretches by 10% (i.e., ΔL = 0.1L0), BII is defined as The inflation index of the balloon decreased from 100% to 82%. This type of BII is defined by the change in balloon shape from a sphere to a prolate spheroid.

[0028] In some embodiments, the processor measures the change in radius using position signals received from electrodes disposed on the membrane of the balloon (e.g., ablation electrodes). The processor measures the change in length using additional position signals received from one or more sensors disposed proximally and / or distally on a shaft coupled to the balloon.

[0029] In other embodiments, for example, if position signals are available only from one or more electrodes disposed on the membrane of the balloon (such as ablation electrodes), the processor may calculate with reasonable accuracy only the change in the radius of the balloon (e.g., the equatorial radius of the balloon). In this case, BII may be defined in a manner that depends solely on the radius. For example, using the balloon curvature k, k = 1 / R, Δk = -ΔR / R 2 In case of corresponding changes in the radius dependence BII2 is defined as When the balloon radius decreases by 10%, BII2 will drop from 100% to 81%.

[0030] Based on the above comparison between the theoretical values of BII1 or BII2, it may be sufficient to determine the degree of balloon occlusion using only the position signals from the electrodes disposed on the balloon membrane. However, in practice, the accuracy of the measured position of the balloon electrodes can be improved by using additional position signals, as described below. Therefore, the actual accuracy of BII1 may exceed the actual accuracy of BII2.

[0031] In one embodiment, the processor provides an indication of the degree of lumen occlusion to the physician in the form of a numerical rating including, for example, a BII value. In another embodiment, the processor outputs a textual indication based on the BII value, such as outputting "very good" for a BII value between, for example, 75% and 84%, or outputting "inadequate" for a BII value between 95% and 100%, or the like.

[0032] Typically, the processor is programmed in software containing specific algorithms that enable the processor to perform each of the processor-related steps and functions described above.

[0033] By providing an indication of the extent to which the ablation balloon has occluded the lumen, for example, via the disclosed BII value, the disclosed technology can improve the accuracy of positioning the balloon catheter against the lumen tissue and thereby improve the effectiveness of balloon ablation. Furthermore, the disclosed technology, which does not require the use of contrast agents for X-ray fluoroscopic imaging, is safe for both patients and physicians.

[0034] The disclosed technology thus provides a complete and safe assessment of each balloon electrode in contact with tissue in real time, which may improve the effectiveness of cardiac balloon ablation therapies, such as pulmonary vein (PV) isolation, as treatments for cardiac arrhythmias.

[0035] System Description

[0036] Figure 1 FIG2 is a schematic diagram of a catheter-based positioning, tracking, and ablation system 20 according to an embodiment of the present invention, comprising a radiofrequency (RF) ablation balloon 40. System 20 includes an active current location (ACL) location tracking subsystem and, optionally, a magnetic location tracking subsystem. In some embodiments, system 20 utilizes balloon 40 to perform RF ablation of an ostium 51 of a PV (shown in FIG25 ). The ACL subsystem is used to estimate the degree of balloon inflation after balloon 40 is inflated within a lumen (e.g., the ostium) to ensure effective subsequent balloon ablation.

[0037] A physician 30 navigates a balloon 40 to a target lumen in a heart 26 of a patient 28 by manipulating the shaft 22 and / or the deflection of the sheath 23 using a manipulator 32 near the proximal end of the catheter. The balloon 40 is inserted through the sheath 23 in a collapsed configuration, and the balloon catheter 40 returns to its intended functional shape only after the balloon is retracted from the sheath 23. By containing the balloon catheter 40 in a collapsed configuration, the sheath 23 also serves to minimize vascular trauma on its way to the target location.

[0038] To determine the degree of inflation of balloon 40, system 20 measures changes in one or more dimensions (e.g., radius and length) of balloon 40. To measure the changes in dimensions, processor 41 of system 20 uses at least position signals from RF ablation electrode 50 (shown in inset 25) of balloon 40, which serves as an ACL sensing electrode for this purpose.

[0039] Electrodes 50 are connected by wires extending through shaft 22 to interface circuitry 44 in console 24 for receiving ACL signals. ACL signals are measured relative to ACL surface electrodes 49, which in the exemplary ACL system are shown attached to the chest and back of patient 28 by wires extending through cable 39. Console 24 drives display 27, which displays the position and, optionally, the shape of balloon 40 within heart 26.

[0040] Electrode position sensing methods based on the ACL using the system 20 are implemented in various medical applications, such as in the CARTO TM 7,756,576, 7,869,865, 7,848,787, and 8,456,182, the disclosures of which are incorporated herein by reference and copies of which are provided in the Appendix.

[0041] As described above, the BII value can be derived using only the position indication signal from the electrode 50. However, to improve accuracy, signals from additional position sensors (such as sensors disposed on the shaft 22 near the balloon 40) can also be used. Methods for improving the accuracy of position measurements using additional signals received from position sensors disposed on the distal end of the shaft (such as from electrodes mounted on the shaft of a catheter located on either side of the balloon) are described in U.S. patent application Ser. No. 15 / 985,149, filed May 21, 2018, entitled “Scaling Impedance Location Measurements of a Balloon Catheter,” which is assigned to the assignee of the present patent application and whose disclosure is incorporated herein by reference.

[0042] In addition or alternatively, additional position signals from a magnetic position sensor mounted in the distal end of shaft 22 may be used. In some embodiments, console 24 also includes a magnetic positioning-sensing subsystem. Patient 28 is placed in a magnetic field generated by a pad containing magnetic field generator coils 42, which are driven by unit 43. The magnetic field generated by coils 42 generates direction signals in magnetic sensor 38, which are then provided as corresponding electrical inputs to processor 41, which uses these to calculate the direction of the distal end of shaft 22 equipped with balloon 40, thereby correcting the position derived using the ACL method.

[0043] Position sensing methods using external magnetic fields are implemented in various medical applications, such as in the CARTO 1000 manufactured by BiosenseWebster Inc. TM The system is implemented in the present invention and is described in detail in U.S. Patents 5,391,199, 6,690,963, 6,484,118, 6,239,724, 6,618,612, and 6,332,089, PCT Patent Publication WO 96 / 05768, and U.S. Patent Application Publications 2002 / 0065455A1, 2003 / 0120150A1, and 2004 / 0068178A1, the disclosures of which are all incorporated herein by reference and copies are provided in the Appendix.

[0044] As described above, in some embodiments, the balloon catheter further includes a distal position sensor 55, which can be a magnetic sensor or a sensing electrode used by the ACL subsystem. Using the additional position signal from sensor 55 in conjunction with the signals from magnetic sensor 38 and / or electrode 50, processor 41 can estimate the change in length of the balloon catheter by estimating the change in the longitudinal distance (i.e., parallel to the distal end of shaft 22) between the positions measured by the various sensors.

[0045] The processor 41 typically comprises a general purpose computer that is programmed with software to perform the functions described herein. Specifically, the processor 41 executes a dedicated algorithm as disclosed herein (including Figure 3 The software may be downloaded to a computer in electronic form over a network, for example, or it may alternatively or additionally be provided and / or stored on a non-transitory tangible medium such as magnetic, optical or electronic memory.

[0046] For simplicity and clarity, Figure 1 Only the elements related to the technology disclosed in the present invention are shown. System 20 typically includes additional modules and elements that are not directly related to the technology disclosed in the present invention and therefore the additional modules and elements are not directly related to the technology disclosed in the present invention. Figure 1 and the corresponding descriptions are intentionally omitted.

[0047] Identifying pulmonary vein occlusion by balloon catheter scale deformation

[0048] Figure 2A and Figure 2B are in a free state and a constrained inflated state, respectively, according to an embodiment of the present invention. Figure 1 Schematic side view of balloon 40.

[0049] like Figure 2A As shown, balloon 40 inflated in free space resembles a sphere having an equator 45 about a longitudinal axis 66 parallel to the distal end of shaft 22. A length 61 is defined between the distal edge of the balloon and the proximal end of the balloon.

[0050] Ablation electrode 50 is shown disposed on membrane 71 of the balloon. Also shown are magnetic sensor 38 located only proximal to balloon 40 and sensing electrode 55 located only distal to the balloon. In some embodiments, the magnetic sensor replaces or is added to sensing electrode 55.

[0051] Figure 2B The balloon 40 is shown inflated to occlude the ostium 51. As shown, as the balloon is pressed against the wall of the ostium, the radius of the equator decreases by a change in radius 60. Additionally, the balloon is characterized by an increasing length 62 along the longitudinal axis 66 of the balloon because the shape of the balloon resembles a prolate spheroid.

[0052] Using the measured change in radius ΔR of equator 45 (e.g., decrease 60) and the measured change in length ΔL from length 61 to length 62 (e.g., increase 64), processor 22 may utilize, for example to derive the BII value.

[0053] where ΔR is the change in the radius of the balloon; R0 is the original radius of the unconstrained balloon; ΔL is the change in the length of the balloon; and L0 is the original length of the unconstrained balloon.

[0054] Figure 2A and Figure 2B The illustrations shown are chosen solely for the sake of conceptual clarity. Other geometries of the ablation electrodes are also possible. Elements not relevant to the disclosed embodiments of the present invention, such as irrigation ports and temperature sensors, have been omitted for clarity.

[0055] Figure 3 To schematically illustrate the method of deriving the effective current position (ACL) measurement result according to an embodiment of the present invention. Figure 2A and Figure 2B Circle 75 represents the equator 45 of the balloon inflated in free space, where the equator 45 has a known radius typically in the range of ten to fifteen millimeters depending on the balloon model.

[0056] The radial position 79 of the electrode 50 ( Figure 3 ) is derived by processor 41 using ACL signals from ablation electrode 50 and surface electrode 49 (i.e., using the aforementioned ACL method). By using, for example, a correction, radial position 79 approximately represents a circle on the plane defined by equator 45. To find radial variation 60, processor 41 fits radial position 79 to circle 77 and calculates radial variation 60 as the difference between the known radius of circle 75 and the radius of fitted circle 77.

[0057] The processor 41 then uses, for example, To calculate BII, where k defined by k = 1 / R is the corresponding curvature of the balloon, Δk, Δk = -ΔR / R 2 is the corresponding change in balloon curvature calculated from the radial change 60ΔR using the average value R of radii 75 and 77.

[0058] BII2 derived solely using signals from ablation electrodes disposed on the membrane of balloon 40 may provide a sufficiently accurate estimate of the degree of occlusion. However, the use of additional position signals, such as from sensors 38 and / or 55 disposed on shaft 22 proximal and distal to balloon 40, respectively, may improve the accuracy of measuring position 79 and, therefore, the accuracy of BII2.

[0059] Figure 4 To schematically illustrate a method for Figure 1Flowchart of a method and algorithm for estimating the degree of occlusion of an ostium with a balloon 40. The algorithm according to the present embodiment performs the following process, which begins at a balloon inflation step 80, where the physician 30 inflates an unconstrained balloon, for example, in a blood pool within the heart. Next, at a first balloon measurement step 82, the system 20 uses the electrodes 50 and the surface electrodes 49 and determines (i.e., measures) unconstrained balloon dimensions, such as the radius of the unconstrained balloon 40, for example, the radius of the equator 45 of the unconstrained balloon 40, via ACL, magnetic, or hybrid ACL and magnetic position sensing technology.

[0060] Next, at a balloon positioning step 84, the physician 30 positions the balloon catheter 40 at a target location within the lumen of the heart 26, such as the ostium of a pulmonary vein. At a constrained balloon measurement step 86, the system 20 uses the electrodes 50 and 55 to measure the radius of the compressed balloon 40, for example, the radius of the equator 45 of the compressed balloon 40. Next, at a balloon dimension change calculation step 88, the processor 41 calculates the change in balloon equatorial radius 60 based on the measured equatorial radius of the freely inflated balloon 40 and the equatorial radius of the compressed balloon.

[0061] In one embodiment, processor 41 applies in step 88 Figure 3 The method described is used to derive the radial variation 60 (ie, the reduction in radius).

[0062] Next, at a BII calculation step 90 , processor 41 uses the calculated change 60 to calculate a balloon inflation index (BII), such as BII2 .

[0063] At an occlusion indication step 92 , based on the calculated balloon inflation index, the system 20 indicates to the physician 30 the degree of occlusion of the ostium, such as by presenting a rating on the display 27 .

[0064] At decision step 94 , physician 30 decides, based on the rating, whether balloon 40 is positioned sufficiently well relative to the ostium.

[0065] If the physician 30 decides that the balloon 40 occludes the ostium sufficiently well, the physician 30 performs treatment such as RF ablation in an RF balloon treatment step 96 .

[0066] On the other hand, if the physician 30 determines that the balloon 40 is not adequately occluding the ostium, the process proceeds to a repositioning step 98 during which the physician 30 attempts to better occlude the ostium. The process then loops back to step 86 to remeasure the constrained balloon dimensions of the constrained balloon and re-estimate the degree of occlusion.

[0067] Figure 4The exemplary flow chart shown in is chosen solely for conceptual clarity. This embodiment also includes additional steps of the algorithm, such as acquiring X-ray images, which have been intentionally omitted from the disclosure herein in order to provide a more simplified flow chart. In addition, other steps, such as applying irrigation, have been omitted for clarity of presentation.

[0068] Although the embodiments described herein are primarily directed to cardiac applications, the methods and systems described herein may also be used in other applications such as otolaryngology, neurology, cardiology, vascular therapy, and renal denervation.

[0069] It should therefore be understood that the embodiments described above are cited by way of example, and that the present invention is not limited to what is specifically shown and described above. On the contrary, the scope of the present invention includes combinations and subcombinations of the various features described above, as well as variations and modifications thereof, which will occur to those skilled in the art upon reading the above description and which are not disclosed in the prior art. The documents incorporated by reference into this patent application are considered an integral part of this application, except that if any term defined in these incorporated documents conflicts with a definition explicitly or implicitly given in this specification, only the definition in this specification shall be considered.

Claims

1. A catheter-based positioning, tracking, and ablation system, comprising: an interface configured to receive a position signal indicative of a position of a plurality of electrodes disposed on an inflatable balloon mounted at a distal end of the shaft for engaging a lumen of an organ to occlude the lumen; as well as a processor configured to: calculating a change in one or more dimensions of the balloon based on the received position signal; using the calculated change in dimension, deriving a balloon inflation index (BII) indicative of an estimated degree of occlusion of the lumen by the balloon, the BII being based at least in part on a corresponding change in balloon curvature between (i) a first configuration in which the balloon is inflated but not engaged in the lumen, and (ii) a second configuration in which the balloon is inflated and engaged in the lumen; as well as The estimated degree of occlusion is presented to the user.

2. The system of claim 1, wherein the BII is derived by the following equation: BII=100(1-(Δk / k)) 2 , where k is the respective curvature of the balloon, and Δk is the respective change in balloon curvature between the first configuration and the second configuration.

3. The system of claim 1 , wherein the processor is configured to calculate the change in scale by calculating a change in a radius of the balloon.

4. The system of claim 3 , wherein the processor is configured to calculate the change in the radius of the balloon by: receiving a measured position of an ablation electrode on the inflatable balloon measured using an effective current position (ACL); fitting the measured positions to a best-fit circle; and The radius of the best-fit circle is calculated.

5. A system according to claim 1, wherein the processor is configured to receive additional position signals from one or more position sensors disposed on the distal end of the shaft, and to calculate the change in scale by calculating a change in the length of the balloon along the longitudinal axis of the balloon based on the additional position signals.

6. The system of claim 1 wherein the processor is configured to estimate the extent to which the balloon occludes the lumen by numerically rating the extent.

7. The system of claim 1, wherein the processor is configured to estimate the extent to which the balloon occludes the lumen by textually rating the extent.

8. The system of claim 1, wherein the lumen comprises an ostium of a pulmonary vein (PV).

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