Verify catheter is properly withdrawn into sheath

Abstract

The invention is entitled "Verifying that a catheter is properly withdrawn into a sheath." The invention discloses a method that includes receiving, in a processor, signals from (i) a first position sensor disposed on a shaft of a catheter and (ii) a second position sensor disposed on a distal end of a sheath of the catheter. Based on the signals received from the first position sensor and the second position sensor, an event is detected in which an expandable distal end assembly of the catheter is withdrawn into the sheath while still at least partially expanded. A responsive action is initiated in response to detecting the event.

Description

Technical Field

[0001] The present invention relates generally to tracking the position and / or shape of a probe in vivo, and more specifically to tracking a balloon catheter. Background Technology

[0002] Techniques for tracking the position and / or shape of in vivo probes, such as catheters, have previously been disclosed in patent literature. For example, U.S. Patent Application Publication 2013 / 0303886 describes a device comprising a sheath configured for insertion into a human patient, the sheath including a lumen and a distal end of the sheath. The device also includes a probe having a distal end configured for insertion through the lumen into the human patient. A magnetic transducer is fixedly attached to the distal end of the sheath and emits a magnetic field, which is picked up by a sensor disposed on the distal end of the probe, thereby allowing measurement of the relative distance between the distal end of the probe and the distal end of the sheath.

[0003] For example, U.S. Patent 6,748,255 describes a basket-shaped conduit comprising a basket-shaped assembly having a proximal end and a distal end, and electrodes mounted on a plurality of ridges connected together at their proximal and distal ends. The conduit also includes a distal position sensor mounted at or near the distal end of the basket-shaped assembly, and a proximal position sensor mounted at or near the proximal end of the basket-shaped assembly. In use, the coordinates of the distal position sensors relative to the coordinates of the proximal sensors can be determined, while simultaneously acquiring known information about the curvature of the ridges of the basket-shaped assembly, to locate the position of at least one electrode in each ridge. Summary of the Invention

[0004] Embodiments of the present invention provide a method comprising receiving signals in a processor from (i) a first position sensor disposed on the axis of a catheter and (ii) a second position sensor disposed on the distal end of a sheath of the catheter. Based on the signals received from the first and second position sensors, an event is detected in which an expandable distal end assembly of the catheter is retracted into the sheath while still at least partially expanded. A response action is initiated in response to the detected event.

[0005] In some implementations, detecting an event includes estimating the extent of expansion of the distal end component and detecting the event based on signals received from a first position sensor and a second position sensor, as well as the estimated extent of expansion of the distal end component.

[0006] In some implementations, the first position sensor is mounted on the proximal side of the distal end assembly.

[0007] In one embodiment, receiving the signals further comprises receiving signals from a third position sensor assembled distally of the distal end assembly, and wherein detecting the event is performed based on the signals received from the first position sensor, the second position sensor, and the third position sensor.

[0008] In another embodiment, detecting the event comprises (a) estimating relative positions of the first position sensor, the second position sensor, and the third position sensor based on the signals, (b) estimating, based on the relative positions of the first position sensor, the second position sensor, and the third position sensor, (i) a sufficiency of a collapse of the expandable distal end assembly, and (ii) a sufficiency of a distal distance of the expandable distal end assembly from a distal edge of the sheath; and (c) detecting the event in response to the sufficiency of the collapse and the sufficiency of the distal distance.

[0009] In some embodiments, computing the position comprises computing a projection of the position on a longitudinal axis defined by a distal end of the shaft.

[0010] In some embodiments, estimating the sufficiency of the collapse comprises computing a length between the estimated position of the first position sensor and the estimated position of the third position sensor, and comparing the computed distance to a pre-specified minimum length.

[0011] In one embodiment, estimating the sufficiency of the distal distance comprises computing a distance between the estimated position of the first position sensor and the estimated position of the second position sensor, and comparing the computed distance to a pre-specified minimum distance.

[0012] In another embodiment, initiating the responsive action comprises sending a warning to a physician.

[0013] In some embodiments, the expandable distal end assembly comprises an inflatable balloon.

[0014] In some embodiments, initiating the responsive action comprises reducing a rate of pumped fluid into the balloon to an idle flow rate.

[0015] In one embodiment, the expandable distal end assembly comprises one of an expandable basket-type end effector or a lasso-type end effector.

[0016] According to an embodiment of the invention, a medical device is further provided, comprising a sheath, a shaft, a first position sensor, and a second position sensor. The sheath extends along a longitudinal axis. The shaft is disposed within the sheath and configured to extend out of the sheath along the longitudinal axis, wherein the shaft includes an expandable member connected to a distal portion of the shaft. The first position sensor is coupled to the shaft to provide a signal indicating the position of the shaft. The second position sensor is coupled to the distal portion of the sheath to provide a signal indicating the position of the sheath, such that the position or direction of movement of the shaft relative to the sheath can be obtained using the first and second position sensors.

[0017] According to an embodiment of the invention, a system comprising a catheter, a sheath, and a processor is further provided. The catheter includes a shaft and a first position sensor coupled to the shaft. The sheath has a second position sensor disposed on its distal end. The processor is configured to: (a) detect an event, based on signals received from the first and second position sensors, in which an expandable distal end assembly of the catheter is retracted into the sheath while still at least partially expanded; and (b) initiate a response action in response to the detected event.

[0018] The invention will be more fully understood through the following detailed description of embodiments thereof, taken in conjunction with the accompanying drawings, wherein: Attached Figure Description

[0019] Figure 1 A schematic diagram illustrating a catheter position tracking system for tracking a balloon catheter within a patient's heart, according to an embodiment of the present invention;

[0020] Figure 2 According to an embodiment of the present invention Figure 1 A schematic diagram illustrating the use of a balloon catheter; and

[0021] Figure 3 The illustration is intended to demonstrate the verification process according to an embodiment of the invention. Figure 2 The flowchart shows the method for withdrawing the balloon catheter back into the sheath. Detailed Implementation

[0022] SUMMARY

[0023] Expandable distal end assemblies for catheters inserted into the cavities of patient organs, such as balloon catheters or basket catheters, can be used in a variety of clinical applications, such as electroanatomical mapping and ablation of cavity walls (e.g., cardiac cavity walls). The expandable distal end assembly is coupled to the distal end of the shaft.

[0024] In a typical procedure, the catheter is inserted into the heart through a sheath with the distal end assembly in a collapsed configuration. Upon exiting the sheath within the heart, the distal end assembly expands into an expanded configuration. Withdrawing (retracting) the catheter into the sheath is accomplished manually by collapsing the distal end assembly, as described below. During the withdrawal process, it is difficult for the physician to know the precise status of the catheter, e.g., whether the distal end assembly is sufficiently collapsed, and the extent to which the catheter is retracted into the distal end of the sheath.

[0025] For example, consider a balloon catheter. The balloon catheter is expanded or collapsed using a balloon advancing member when in place outside the sheath. The collapsed balloon is withdrawn from the body by pushing the advancing member distally to elongate and contract the balloon. The shaft of the catheter is then pulled back to retract the contracted balloon into the sheath. However, if the physician does not verify proper elongation of the balloon (i.e., full collapse) during the withdrawal phase, the withdrawal will require excessive force and can damage the catheter.

[0026] Embodiments of the present invention described below combine knowledge of the sufficiency of balloon collapse and the sufficiency of the distal distance of the balloon from the distal end of the sheath in order to verify proper withdrawal of the balloon from the patient's body. In some embodiments, the processor determines during the balloon withdrawal phase that (i) the balloon is not sufficiently collapsed and (ii) the balloon is at least partially within the sheath. In this case, a warning is sent to the physician that the balloon is being attempted to be withdrawn while not ready for withdrawal (i.e., the balloon is still too expanded). In addition, the processor can initiate steps to modify the situation, as described below.

[0027] In some embodiments, the processor receives signals from (i) a first position sensor disposed on a shaft of the catheter and (ii) a second position sensor disposed on a distal end of a sheath of the catheter. Based on the signals received from the first position sensor and the second position sensor, the processor detects an event in which the expandable distal end assembly of the catheter is withdrawn into the sheath while still at least partially expanded, and initiates a responsive action in response to detecting the event. In one embodiment, detecting the event includes estimating a degree of expansion of the distal end assembly, and detecting the event is based on the signals received from the first position sensor and the second position sensor and on the estimated degree of expansion of the distal end assembly.

[0028] In another embodiment, the processor is further configured to receive the signals by receiving signals from a third position sensor fitted distally on the distal end assembly, and wherein detecting the event is performed based on the signals received from the first position sensor, the second position sensor, and the third position sensor.

[0029] In other embodiments, the processor receives signals from (i) a first proximal position sensor and a third distal position sensor disposed on the shaft of the catheter on either side of an expandable distal end assembly (e.g., a balloon) assembled at the distal end of the shaft, and (ii) a second sheath position sensor disposed on the distal end of the sheath of the catheter. Based on the signals received from the proximal position sensor, the distal position sensor, and the sheath position sensor, the processor detects an event in which the expandable distal end assembly is withdrawn into the sheath while still at least partially expanded, and initiates a responsive action, such as alerting the physician, in response to detecting the event.

[0030] In some embodiments, the processor determines that the balloon is not sufficiently collapsed by comparing the length E of the balloon to a pre-specified minimum collapsed length E0. The processor determines that the balloon has an insufficient distal distance from the distal edge of the sheath (e.g., the balloon is at least partially within the sheath) by comparing the measured distance A between the proximal position sensor on the shaft and the position on the distal end of the sheath to a minimum length A0. In one embodiment, if E < E0 and A < A0, the processor determines that the balloon is being attempted to be withdrawn while not sufficiently collapsed, and issues a warning.

[0031] In addition to or alternatively to the warning, the processor can reduce the rate of pumped fluid into the balloon (which, if too high, causes the balloon to remain inflated) to an idle flow rate. In addition to or alternatively to this, any other suitable responsive action can be taken.

[0032] The distance A is measured using one or more additional position sensors disposed on the distal end of the sheath and referred to hereinafter as “sheath position sensors.” Based on position signals from the sheath position sensors, the processor of the system can calculate the distance along the longitudinal axis defined by the distal end of the shaft between the proximal balloon sensor and the position of the sheath sensor. Using the calculated distance and known catheter geometry, the processor can compare the distance A to a pre-specified minimum distance A0.

[0033] The sheath position sensors are typically magnetic position sensors. But other sensor types can be used to enable the processor to derive the relative position of the sheath distal end and the balloon proximal sensor based on positions measured in a coordinate system used by the processor. For example, the sheath sensors can be electrodes disposed on the distal end of the sheath.

[0034] Typically, the processor is programmed with software containing specific algorithms that enable the processor to perform each of the processor-related steps and functions listed above.

[0035] By combining the adequacy of the balloon distal position relative to the sheath with the adequacy of the balloon collapse, embodiments of the present invention enable a physician operating a balloon catheter to safely retract the balloon within the sheath.

[0036] By way of example, the embodiments described herein are primarily directed to balloon catheters. However, the technology disclosed herein is equally applicable to other types of expandable / collapsible distal end assemblies, such as basket catheters.

[0037] System Description

[0038] Figure 1 A schematic illustration of a catheter position tracking system 20 for tracking a balloon catheter within a patient's heart in accordance with an embodiment of the present invention. The illustrated system 20 includes both an electrical position tracking subsystem and a magnetic position tracking subsystem. The system 20 is used to determine the position of a balloon catheter 40 shown in inset 25 assembled at a distal end of a shaft 22, and the extent to which the balloon is collapsed prior to an attempted withdrawal through a sheath 23. Typically, the balloon catheter 40 is used for therapeutic treatment, such as spatially ablating cardiac tissue, for example at the left atrium.

[0039] The balloon catheter 40 includes a proximal position sensor 50 and a distal position sensor 52 assembled on the shaft 22 on either side of the balloon. A sheath position sensor 54 is disposed on a distal end of the catheter's sheath 23. The proximal position sensor 50 and the distal position sensor 52 are connected by wires through the shaft 22 to various drive circuits in a console 24. The sheath position sensor 54 is disposed at a distal portion of the sheath 23 Figure 2 ) and is connected by wires that first pass through the sheath 23 and then connect to various drive circuits in the console 24.

[0040] Typically, the proximal position sensor 50, the distal position sensor 52 and the sheath position sensor 54 include magnetic sensors or electrodes. The magnetic sensors or electrodes are used by the magnetic position tracking subsystem or the electrical position tracking subsystem, respectively, as described below.

[0041] The physician 30 navigates the balloon catheter 40 to a target location in the patient's 28 heart 26 by manipulating the shaft 22 using a manipulator 32 proximate to the catheter's proximal end and / or by flexing the sheath 23. The balloon catheter 40 is inserted through the sheath 23 in a collapsed configuration, and only after the sheath 23 is retracted and the balloon advance member is subsequently retracted, does the balloon catheter 40 resume its intended functional shape. By including the balloon catheter 40 in a collapsed configuration, the sheath 23 also serves to minimize vascular trauma on its way to the target location.

[0042] The console 24 includes a processor 41 (typically a general purpose computer) with suitable front end and interface circuitry 44 for receiving signals from various sensors in and on the patient 28.

[0043] In some embodiments, the processor 41 accurately determines position coordinates of the proximal position sensor 50, the distal position sensor 52, and the sheath position sensor 54 within the heart 26. Examples of processor coordinate systems can include those used by various position tracking systems such as the aforementioned electrical position tracking subsystem and the magnetic position tracking subsystem.

[0044] In one embodiment, the processor 41 determines position coordinates based on, among other inputs, measured impedances between electrodes used as one or more of the position sensors 50, 52, and 54 and surface electrodes 49. The processor 41 is connected to the surface electrodes 49 by wires that extend through the cable 39 to the chest of the patient 26, which in the exemplary system is shown as being attached to the skin of the patient 28.

[0045] Methods of electrode position sensing using the electrical position tracking subsystem of the system 20 are implemented in various medical applications, for example, using the advanced catheter location (ACL) method in the CARTO® system produced by Biosense-Webster Inc. (Irvine, California), and described in detail in U.S. Patents 7756576, 7869865, 7848787, and 8456182, which prior patent applications are hereby incorporated by reference in their entireties into this application as if set forth in full in the appendix. TM

[0046] Using the sensed electrode positions, a multi-electrode catheter such as a balloon catheter, basket catheter, LASSO® catheter, NMARQ® catheter, or other catheter can be estimated. TM TM ​​The shape of the catheter (both of which are manufactured by Biosense Webster, as well as other multi-electrode capable flexible catheters) and the corresponding degree of collapse (or restriction) of the expandable or flexible distal tip assembly can be estimated. Examples of catheters in the form of a lasso with an end effector are shown in and described in US9788893; US6973339; US8475450; US8600472; US9050010; US9220433; US9848948; US8608735; US7371232; US20170100188, which are incorporated by reference in their entirety. Thus, in conjunction with the known distance between the proximal sensor and the sheath sensor, the ACL method can be used with the presently disclosed embodiments that do not include a distal position sensor to detect the event in which the expandable distal tip assembly is withdrawn into the sheath while still at least partially expanded or flexed.

[0047] For example, the aforementioned US patent 8456182, which has a method of "local calibration" hereinafter referred to as "independent current localization" (ICL), is applicable to a catheter provided with a plurality of sensing electrodes on its distal end. Using the known spatial relationship between two or more electrodes, for example, one or more known distances between the electrodes, the ICL method is capable of calibrating the relative positions of the plurality of electrodes in order to accurately estimate the shape of the expandable distal tip assembly of the catheter.

[0048] In some embodiments, the presently disclosed method uses the sheath position sensor and the proximal position sensor and the ACL and ICL derived shape of the expandable distal tip assembly to detect the event in which the expandable distal tip assembly is withdrawn into the sheath while still at least partially expanded or flexed. In such embodiments, the distal position sensor can be omitted.

[0049] In general, there can be many techniques to estimate the shape of the expandable distal tip assembly (and in particular to estimate the degree of expansion of the distal tip assembly). As another example, the shape can be estimated using magnetic position sensors provided on the expandable distal tip assembly. For example, US patent application 16 / 198487, filed November 21, 2018, entitled "Configuring Perimeter of Balloon Electrode as Location Sensor", describes a plurality of magnetic coils provided on a balloon to be used as a location sensor, which document is incorporated by reference and whose copy is provided in the appendix.

[0050] In U.S. Patent Application 16 / 198487, the spatial configuration of an expandable balloon within an organ is estimated. It is noted here that the estimation can include at least one of estimating the flexing of the balloon relative to a longitudinal axis defined by the distal end of the shaft and estimating the shape of the balloon within the organ. The step of estimating the shape can include identifying the degree of expansion of the balloon or detecting whether the balloon is fully expanded.

[0051] In one embodiment, the balloon shape is estimated in the form of an "inflation index" which gives the level of balloon inflation in a dimensionless number. Similarly, an expansion index can be provided for any expandable distal end assembly.

[0052] As noted above, the system 20 also includes a magnetic sensing subsystem. The patient 28 is placed in a magnetic field generated by a mat containing magnetic field generator coils 42, which are driven by a unit 43. The magnetic field generated by the coils 42 generates signals in any magnetic position sensors, which are then provided as corresponding electrical inputs to the processor 41, which uses these inputs to calculate the position of any of the position sensors 50, 52 and 54, including the magnetic sensor.

[0053] The method of position sensing using an external magnetic field is implemented in various medical applications, for example in the CARTO® system produced by Biosense Webster Inc. TM and described in detail in U.S. Patents 5391199; US5558091; US6172499; US6177792; US6788967 and 6690963, and PCT Patent Publication WO 96 / 05768, the disclosures of which are incorporated herein by reference and copies of which are provided in the Appendix.

[0054] With the tracked position, the console 24 can drive a display 27 which displays the distal end of the catheter position within the heart 26.

[0055] The processor 41 is generally programmed in software to perform the functions described herein. The software can be downloaded to the computer in electronic form, over a network, for example, or it can alternatively or additionally be provided and / or stored on non-transitory tangible media, such as magnetic, optical or electronic memory. In particular, the processor 41 runs a special purpose algorithm of the steps of the present disclosure described. Figure 3 The special purpose algorithm of the steps of the present disclosure described.

[0056] For simplicity and clarity, the illustrative embodiments of the application will be described Figure 1Only a few techniques related to the disclosed invention have been illustrated. For example, another electrical-based position measurement method can be used, in which a voltage gradient is applied between surface electrodes 49 and a position signal is derived from the voltage measurement results obtained from the body electrodes.

[0057] An exemplary technical description for estimating the elongation of an expandable component is provided in U.S. Patent Application 16 / 234604, filed December 28, 2018, entitled “Finding Elongation of Expendable Distal End of Catheter,” which has been assigned to the assignee of this patent application and the disclosure thereof is incorporated herein by reference.

[0058] Verification of balloon catheter withdrawal into sheath

[0059] Figure 2 According to an embodiment of the present invention Figure 1 A schematic diagram illustrating the balloon catheter. The balloon 40 is mounted at the distal end of shaft 22, which defines a longitudinal axis 51. A proximal position sensor 50 is mounted on shaft 22, while a distal position sensor 52 is mounted on the distal end of balloon propulsion member 55, such that the position sensors are located on either side of the balloon 40, which... Figure 2 The sleeve is shown in a partially collapsed configuration. A sleeve position sensor 54 mounted on the distal end of the sleeve 23 is also shown.

[0060] After the doctor has pushed the propulsion component 55 distally to elongate and contract the balloon 40, the balloon 40 catheter collapses and contracts at least partially.

[0061] In the technique disclosed in this invention, the processor 41 calculates the distance 60 (Δ) along the longitudinal axis 51 between the position of the sheath position sensor 54 and the position of the proximal position sensor 50. If the proximal position sensor 50 is sufficiently located within the sheath 23 and extends beyond the sheath position sensor 54, then the distance 60 is negative, i.e., Δ < 0. The processor 41 also calculates the length 66 (E) of the balloon 40 by calculating the distance along the longitudinal axis 51 between the position of the proximal position sensor 50 and the position of the distal position sensor 52.

[0062] Based on comparing the distance 60 and length 66 with a pre-specified minimum distance Δ0 and a pre-specified minimum length E0, respectively, the processor 41 can determine whether to attempt to retract the balloon 40 into the sheath 23 if the balloon 40 has not fully collapsed.

[0063] Figure 2The examples shown are chosen for clarity of concept. Elements not relevant to the disclosed embodiments of the application, such as additional sensors, are omitted for clarity. As noted above, in some embodiments, using a sheath position sensor and a proximal position sensor, and the derivation of the shape of the expandable distal end assembly (e.g., using ACL and ICL, or other means), an event is detected in which the expandable distal end assembly is withdrawn into the sheath while still at least partially expanded.

[0064] Figure 3 A flowchart of a method for verifying that the balloon 40 is withdrawn into the sheath 23 according to an embodiment of the application is shown schematically. According to the provided embodiment, the algorithm performs the following process, which begins at a position signal receiving step 70, in which the processor 41 receives signals from the proximal position sensor 50, the distal position sensor 52, and the sheath position sensor 54. Figure 2

[0065] Next, at position estimating steps 72, 74, and 76, respectively, the processor 41 estimates the positions of the proximal position sensor 50, the distal position sensor 52, and the sheath position sensor 54 using the position signals. In one embodiment, the processor is configured to calculate the positions by calculating the projections of the positions on the longitudinal axis 51.

[0066] At a distance 60 calculating step 78, the processor 41 calculates the distance 60 of the balloon 40 from the distal edge of the sheath 23 using the positions calculated at steps 74 and 76.

[0067] At a length 66 calculating step 80, the processor 41 calculates the length 66 (E) of the balloon 40 from the distal edge of the sheath 23 using the positions calculated at steps 72 and 74.

[0068] Using the distance 60, the processor 41 estimates the insufficiency of the distal distance of the inflatable balloon from the distal edge of the sheath, for example, by checking at a distal distance insufficiency estimating step 82 whether Δ≤Δ0(as described above).

[0069] Using the length 66, the processor 41 estimates the insufficiency of the collapse of the inflatable balloon, for example, by checking at a collapse insufficiency estimating step 84 whether E≤E0(as described above).

[0070] If either of the answers to the questions in steps 82 and 84 is negative, the processor 41 causes the process to loop back to step 70 to continue monitoring the distal distance of the balloon from the sheath and whether the balloon is sufficiently collapsed.

[0071] ​If both the distal distance and the collapse are deemed insufficient (i.e., both answers are "yes"), the processor 41 alerts the physician 30 at alert step 86 to attempt to withdraw the balloon into the sheath while the balloon is not fully collapsed. In any case, the process returns to step 70 to acquire new position data.

[0072] Figure 3 The exemplary flowchart shown in FIG. 5 is chosen for conceptual clarity only. Additional steps can be performed subsequently, such as reducing the fluid pumping rate to help collapse the balloon 40.

[0073] While the embodiments described herein primarily relate to balloon catheters, the methods and systems described herein can also be used with other types of catheters having a distal end that can be expanded, such as basket catheters, collar catheters that require the collar to be in the maximally expanded position, and flexible catheters that require the catheter not to flex before the catheter is withdrawn into the sheath. For collar catheters and flexible catheters, the diameter of the collar or the curvature of the catheter are the key factors to monitor, while the distance E is secondary.

[0074] It should therefore be understood that the embodiments described above are cited by way of example, and that the present application is not limited to what has been particularly shown and described hereinabove. Rather, the scope of the present application includes both combinations and sub-combinations of the various features described hereinabove, as well as variations and modifications thereof, which would occur to persons of ordinary skill in the art upon reading the foregoing description and which are not disclosed in the prior art. Documents incorporated by reference in the present patent application are to be considered an integral part of the application except that to the extent any terms are defined in such incorporated documents in a manner that conflicts with the definitions made explicit herein, the definitions made explicit in this application shall prevail. In closing, the claims set forth below are intended to describe the scope of the application.

Claims

1. A system comprising: a catheter including: a shaft; a first position sensor coupled to the shaft; a sheath having a second position sensor disposed on a distal end thereof; and a processor configured to: detect, based on respective signals received from the first position sensor and the second position sensor, an event in which an expandable distal end assembly of the catheter is withdrawn into the sheath while still at least partially expanded; and initiate a responsive action in response to detecting the event, and wherein the processor is further configured to receive signals from a third position sensor assembled distally of the distal end assembly and to detect the event based on the signals received from the first position sensor, the second position sensor, and the third position sensor.

2. The system of claim 1, wherein the processor is configured to detect the event by estimating a degree to which the distal end assembly is expanded and detecting the event based on the signals received from the first position sensor and the second position sensor and based on the estimated degree to which the distal end assembly is expanded.

3. The system of claim 1, wherein the first position sensor is assembled proximally of the distal end assembly.

4. The system of claim 1, wherein the processor is configured to detect the event by: estimating, based on the signals, relative positions of the first position sensor, the second position sensor, and the third position sensor; estimating, based on the relative positions of the first position sensor, the second position sensor, and the third position sensor, (i) a sufficiency of collapse of the expandable distal end assembly and (ii) a sufficiency of distal distance of the expandable distal end assembly from the distal edge of the sheath; and detecting the event in response to the sufficiencies of collapse and distal distance.

5. The system of claim 4, wherein the processor is configured to compute the positions by computing projections of the positions on a longitudinal axis defined by the distal end of the shaft.

6. The system of claim 4, wherein the processor is configured to estimate the sufficiency of collapse by computing a length between the estimated position of the first position sensor and the estimated position of the third position sensor and comparing the computed distance to a pre-specified minimum length.

7. The system of claim 4, wherein the processor is configured to estimate a sufficiency of distal distance by computing a distance between the estimated position of the first position sensor and the estimated position of the second position sensor and comparing the computed distance to a pre-specified minimum distance.

8. The system of claim 1, wherein the processor is configured to initiate the responsive action by sending a warning to a physician.

9. The system of claim 1, wherein the expandable distal end assembly includes an inflatable balloon.

10. The system of claim 9, wherein the processor is configured to initiate the responsive action by reducing a rate of pumped fluid into the balloon to an idle flow rate.

11. The system of claim 1, wherein the expandable distal end assembly comprises an expandable basket.

12. The system of claim 1, wherein the expandable distal end assembly comprises a lasso.

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