CN117898821A - Basket catheter with porous sheath - Google Patents

Abstract

The invention discloses a medical device, comprising: an insertion tube configured for insertion into a body cavity of a patient; and an inflatable assembly distally connected to the insertion tube and including an electrode configured to apply electrical energy to tissue within the body lumen. A flexible porous sheath is mounted on the inflatable assembly and is configured to contact tissue within the body lumen such that the electrical energy is applied from the electrode to the tissue through the sheath.

Description

Basket catheter with porous sheath

Cross Reference to Related Applications

The present application claims priority from U.S. provisional patent application No. 63/274,334, previously filed on 1 at 11/2021, which provisional patent application is hereby incorporated by reference in its entirety.

Technical Field

The present invention relates generally to invasive medical equipment, and in particular to devices for ablating tissue in the body and methods for making and using such devices.

Background

Arrhythmia is typically treated by ablation of myocardial tissue in order to block the arrhythmogenic electrical pathway. To this end, a catheter is inserted into the heart chamber through the vascular system of the patient and one or more electrodes at the distal end of the catheter are brought into contact with the tissue to be ablated. In some cases, high power Radio Frequency (RF) electrical energy is applied to the electrodes in order to thermally ablate the tissue. Alternatively, a high voltage pulse may be applied to the electrode to ablate tissue by irreversible electroporation (IRE).

Some ablation procedures use basket catheters in which a plurality of electrodes are arrayed along the spine of the inflatable assembly at the distal end of the catheter. The ridges curve outwardly to form a basket-like shape and contact tissue within the body cavity. For example, U.S. patent application publication 2020/0289197 describes devices and methods for electroporation ablation therapy, wherein the device includes a set of ridges coupled to a catheter for medical ablation therapy. Each ridge of the set of ridges may include a set of electrodes formed on the ridge. The set of ridges may be configured to transition between a first configuration and a second configuration.

Disclosure of Invention

Embodiments of the invention described below provide improved devices for ablating tissue in vivo, as well as methods for making and using such devices.

There is thus provided, in accordance with an embodiment of the present invention, a medical device including: an insertion tube configured for insertion into a body cavity of a patient; and an inflatable assembly distally connected to the insertion tube and including an electrode configured to apply electrical energy to tissue within the body lumen. A flexible porous sheath is mounted on the inflatable assembly and is configured to contact tissue within the body lumen such that the electrical energy is applied from the electrode to the tissue through the sheath.

There is also provided, in accordance with an embodiment of the present invention, a method for preparing a medical device, the method comprising: providing an insertion tube configured for insertion into a body cavity of a patient; and distally connecting an expandable assembly including an electrode to the insertion tube. A flexible porous sheath is assembled over the inflatable assembly such that the sheath contacts tissue within the body cavity when the insertion tube is inserted into the body cavity.

Drawings

The above-described and further aspects of the present invention will be further discussed with reference to the following description, taken in conjunction with the accompanying drawings, in which like numerals indicate like structural elements and features in the various figures. The drawings are not necessarily to scale, emphasis instead being placed upon illustrating the principles of the invention. The drawings depict one or more implementations of the present apparatus by way of example only and not by way of limitation.

FIG. 1 is a schematic illustration showing a system for cardiac ablation according to an embodiment of the present invention;

FIG. 2 is a schematic side view of a catheter expandable assembly having a porous sheath according to an embodiment of the present invention;

FIGS. 3A and 3B are schematic cross-sectional views of the catheter expandable assembly of FIG. 2 in a collapsed configuration and an expanded configuration, respectively, in accordance with an embodiment of the invention;

FIG. 4 is a flow chart schematically illustrating a method for preparing a catheter expandable assembly sheath according to an embodiment of the present invention;

FIG. 5 is a schematic side view of a system for preparing a sheath of a catheter basket assembly according to an embodiment of the present invention;

FIG. 6 is a schematic side view of a braided tube made using the system of FIG. 5 in accordance with an embodiment of the invention;

FIG. 7A is a side view of an exemplary expandable member that may be used with the woven outer cover of FIG. 6, in accordance with an embodiment of the invention; and

Fig. 7B is a side view of yet another expandable member that may be used with the braided outer cover of fig. 6 in accordance with an embodiment of the invention.

Detailed Description

As used herein, the term "about" or "approximately" for any numerical value or range indicates a suitable dimensional tolerance that allows a collection of parts or components to achieve the intended purpose thereof as described herein. More specifically, "about" or "approximately" may refer to a range of values of ±10% of the recited values, for example "about 90%" may refer to a range of values from 81% to 99%.

In addition, as used herein, the terms "patient," "host," "user," and "subject" refer to any human or animal subject, and are not intended to limit the system or method to human use, but use of the subject invention in a human patient represents a preferred embodiment. Likewise, the term "proximal" refers to a location closer to the operator, while "distal" refers to a location further from the operator or physician.

As used herein, the terms "tubular" and "tube" are to be understood broadly and are not limited to structures that are right circular cylinders or that are entirely circumferential in cross-section or that have a uniform cross-section throughout their length. For example, a tubular structure or system is generally shown as a substantially right circular cylinder structure. However, the tubular system may have a tapered or curved outer surface without departing from the scope of the invention.

Basket catheters can be used to quickly and efficiently perform ablation procedures because the spine of the basket catheter (and thus the electrodes on the spine) can contact and ablate tissue at multiple locations simultaneously. However, due to interference caused by the ridges in the blood flow, and due to arcing between the ridges, the ridges themselves may create dangerous blood clots during the ablation procedure, especially in IRE-based ablations. Furthermore, ridges may become embedded in tissue during a procedure, which may lead to localized overheating, resulting in charring and/or other trauma. The use of ridges with smooth rounded contours may help mitigate these effects, but does so without eliminating coagulation and tissue damage problems.

Embodiments of the invention described herein address these problems by covering the inflatable component with a porous sheath. As used herein, the term "sheath" is intended to include an "outer cover" or "membrane". The sheath prevents direct contact between the ridge and the tissue while still allowing electrical energy to be applied from the electrode to the tissue through the sheath. The material type and thickness of the sheath may be selected such that irrigation fluid delivered through the catheter to the inflatable assembly may be delivered outwardly through the sheath to tissue while still preventing blood from penetrating inwardly from the body lumen through the sheath. Thus, the sheath can be used to prevent both coagulation and tissue damage.

Based on these principles, the disclosed embodiments provide a medical device that includes an insertion tube for insertion into a body cavity of a patient and an inflatable assembly distally connected to the insertion tube. The flexible porous sheath is assembled over the inflatable assembly such that the sheath contacts tissue within the body lumen. The inflatable assembly includes an electrode that applies electrical energy through the sheath to tissue within the body lumen. While the embodiments described below relate specifically to basket catheters for intracardiac ablation, the principles of the present invention are applicable to other types of protocols for applying electrical energy to biological tissue.

In some embodiments, the electrical signal generator applies electrical energy to the electrodes on the expandable assembly at an amplitude sufficient to ablate tissue contacted by the spine. In one embodiment, the electrical signal generator applies bipolar electrical pulses to the electrode with sufficient amplitude such that electrical energy applied from the electrode through the sheath causes irreversible electroporation (IRE) in the tissue. Additionally or alternatively, the electrical signal generator applies a Radio Frequency (RF) current to the electrode with sufficient power such that electrical energy applied from the electrode through the sheath causes thermal ablation of the tissue.

Fig. 1 is a schematic pictorial illustration of a system 20 for use in an ablation procedure, in accordance with an embodiment of the present invention. The elements of system 20 may be based on those produced by Bernsted Webster (California, biosense Webster, inc. (Irvine, california))Components of the system.

Physician 30 navigates catheter 22 through the vascular system of patient 28 into the chamber of patient's heart 26, and then deploys inflatable assembly 40 (or 40') fitted with a flexible porous sheath (as shown in detail in fig. 2, 3A, and 3B) at the distal end of catheter 22. The proximal end of the expandable assembly 40 (or 40') is connected to the distal end of the insertion tube 25, which is maneuvered by the physician 30 using the manipulator 32 near the proximal end of the catheter 22. The expandable assembly 40 is inserted in a collapsed configuration through the tubular delivery sheath 23 through the vascular system of the patient 28 into the heart chamber in which the ablation procedure is to be performed. Once inserted into the heart chamber, the expandable assembly 40 (or 40') is deployed from the tubular sheath and allowed to expand within the chamber. Catheter 22 is connected at its proximal end to console 24. The display 27 on the console 24 may present a map 31 or other image of the heart chamber, wherein the map identifies the location of the expandable assembly 40 (or 40') in order to assist the physician 30 in locating the expandable assembly at the target location of the ablation procedure.

Once the expandable assembly 40 (or 40') is properly deployed and positioned in heart 26, physician 30 actuates electrical signal generator 38 in console 24 to apply electrical energy (such as IRE pulses or RF waveforms) to electrodes on the expandable assembly under the control of processor 36. The electrical energy may be applied in bipolar mode between a pair of electrodes on the inflatable assembly 40 (or 40 '), or in monopolar mode between an electrode on the inflatable assembly 40 (or 40 ') and a separate common electrode (e.g., conductive back patch 41) applied to the patient's skin. During an ablation procedure, irrigation pump 34 delivers an irrigation fluid, such as saline solution, to inflatable assembly 40 (or 40') through insertion tube 25.

Typically, catheter 22 includes one or more positioning sensors (not shown in the figures) that output positioning signals indicative of the position (location and orientation) of inflatable assembly 40 (or 40'). For example, the inflatable module 40 (or 40') may incorporate one or more magnetic sensors that output an electrical signal in response to an applied magnetic field. The processor 36 receives and processes the signals to find the position and orientation coordinates of the inflatable assembly 40 (or 40') using techniques known in the art, and implemented, for example, in the Carto system described above. Alternatively or additionally, the system 20 may apply other location sensing techniques in order to find the coordinates of the inflatable assembly 40 (or 40'). For example, the processor 36 may sense the impedance between the electrodes on the inflatable assembly 40 (or 40') and the body surface electrodes 39 applied to the chest of the patient 28, and may convert the impedance to position coordinates using techniques also known in the art. In any event, processor 36 uses the coordinates to display the location of inflatable assembly 40 (or 40') on map 31.

Alternatively, the catheter 22 and ablation techniques described herein may be used without benefiting from position sensing. In such embodiments, for example, fluoroscopy and/or other imaging techniques may be used to determine the location of the expandable assembly 40 (or 40') within the heart 26.

The system configuration shown in fig. 1 is presented by way of example for conceptual clarity in understanding the operation of embodiments of the present invention. For simplicity, fig. 1 only shows elements of system 20 that specifically relate to an inflatable assembly 40 and an ablation procedure using the inflatable assembly. As used herein, the term "expandable assembly" includes any of assemblies 40 (fig. 2, 3A, 3B, and 7A) or 40' (fig. 7B). The remaining elements of the system will be apparent to those skilled in the art, and those skilled in the art will likewise appreciate that the principles of the present invention may be implemented in other medical treatment systems using other components. All such alternative implementations are considered to be within the scope of the present invention.

Reference is now made to fig. 2, 3A and 3B, which schematically illustrate details of an inflatable assembly 40 covered by a flexible outer cover or porous sheath 60, according to an embodiment of the present invention. Fig. 2 is a side view of the expandable assembly 40 in its expanded state, while fig. 3A and 3B are cross-sectional views showing the expandable assembly 40 in a collapsed state and an expanded state (with an outer cover), respectively.

The expandable assembly 40 has a distal end 48 and a proximal end 50 that is connected to a distal end 52 of the insertion tube 25. The inflatable assembly includes a plurality of ridges 44, the proximal ends of which are joined at a proximal end 50, and the distal ends of which are joined at a distal end 48. One or more electrodes 54 are externally disposed on each ridge 44. Alternatively, the ridge 44 may comprise a solid conductive material, and thus may serve as the electrode itself, for example as described in U.S. patent application 16/842,648 (BIO 6265USNP 1) (published as U.S. patent publication 2021/0307815A 1), filed on 7, 4/2020, the disclosure of which is incorporated herein by reference.

Irrigation outlets 56 in the ridge 44 allow irrigation fluid flowing within the ridge 44 to exit and irrigate tissue adjacent the electrode 54. Alternatively or additionally, the irrigation outlet may be located elsewhere in the inflatable assembly, for example on an irrigation manifold (not shown) contained within the inflatable assembly.

Sheath 60 fits over expandable assembly 40 and thus contacts tissue in heart 26 as the expandable assembly expands and advances against the tissue. Sheath 60 prevents direct contact between ridge 44 and heart tissue. Thus, electrical energy applied to the electrode 54 passes through the sheath 60 to the tissue. In one embodiment, sheath 60 comprises expanded polytetrafluoroethylene (ePTFE), for example, having a thickness of about 70 μm. The ePTFE sheath is advantageous in terms of lubrication, smoothness, robustness, and biocompatibility, and prevents the ridge 44 from embedding into cardiac tissue.

Alternatively, the sheath 60 comprises a tube made by braiding suitable polymer fibers, such as polyethylene terephthalate (PET) or polyamide (nylon) yarns. The tube may be braided with a variable diameter to better conform to the deployed basket shape. In particular, the proximal diameter of the tube may be made to fit the proximal neck of the basket, and the distal diameter may be made as small as possible. The distal end may be closed by fastening the loose yarn ends with an adhesive, fusing the yarn ends together, or any other suitable sealing method. The advantage of using a fabric that is tubular rather than flat is that the material conforms better to the basket shape and wrinkling is avoided or minimized. Avoiding folds helps reduce the collapsed diameter of the sheath 60 and also reduces the likelihood of blood clotting in the material folds. The process for preparing such a braided sheath is further described below with reference to fig. 4-6.

In yet another embodiment, sheath 60 is made from a sheet of flexible, non-porous material and holes of a desired size are drilled in the material, such as by laser drilling. In yet another embodiment, the sheath 60 may be formed by blow molding a smaller tubular member to form a balloon membrane, followed by laser drilling holes through the balloon membrane.

The holes in the sheath 60 are large enough to allow irrigation fluid to pass outwardly through the sheath 60 from the irrigation outlet 56 to irrigate heart tissue while preventing blood from penetrating inwardly through the sheath from the heart chamber. The inventors have found that it is advantageous for the holes 103 (fig. 6) in the sheath 60 to have a hole area of about 10 μm ² to about 100,000 μm ². The best results were obtained with holes having an area of about 100 μm ² to about 10,000 μm ². These ranges of aperture areas 103 may also be used to ensure that irrigation fluid (which is electrically conductive) may flow through the aperture areas 103 from the interior of the sheath 60 and out of the porous membrane, sheath 60, to allow electrical energy from the electrode 54 to pass freely through the sheath 60 to adjacent tissue in order to ablate the tissue.

The polymer fibers used to make the sheath 60 (such as PET and nylon fibers) are themselves insulators. However, both PET and nylon are hygroscopic, and once the fibers absorb water or irrigation fluid, they become more conductive, thus allowing the electrical energy output by the electrode 54 to pass more freely through the sheath 60 to the target tissue. To enhance the performance of the sheath 60 in this regard, in one embodiment, the polymer fibers are coated with a hydrophilic material. The hydrophilic coating attracts water into the fibers so that the sheath 60 becomes more conductive, thus facilitating efficient ablation. The coating also makes the sheath more lubricious so that blood cells do not adhere to the fibers of the sheath.

In an alternative embodiment, a hydrophobic coating is applied to the polymer fibers of the sheath 60. The hydrophobic coating requires that the sheath 60 be pressurized in order for the flushing fluid to flow through it. This positive pressure prevents blood from entering sheath 60 even when the flush is at a low flow rate.

In the collapsed state of fig. 3A, ridges 44 are straight and aligned parallel to longitudinal axis 42 of insertion tube 25 to facilitate insertion of expandable assembly 40 into heart 26. In this state, the sheath 60 collapses inwardly along with the ridge 44. To ensure that the sheath 60 is able to collapse with the expandable assembly 40, the sheath 60 is engaged at the distal end 48 and the proximal end 50 of the expandable assembly 40. As the actuator 46 is extended to separate the distal end 48 and the proximal end 50, both the sheath 60 and the ridge 44 will compress into the tubular profile of fig. 3A. Upon retraction of the actuator toward the proximal end 50, the ridge 44 and sheath 60 will expand into the spherical configuration shown in fig. 3B. In the expanded state of fig. 3B, ridges 44 flex radially outward, causing sheath 60 to expand and contact tissue within the heart.

In one embodiment, the ridges 44 are produced such that the steady state of the expandable assembly 40 is the collapsed state of fig. 3A. In this case, as the expandable assembly 40 is pushed out of the sheath, it expands by pulling an actuator 46 (such as a suitable wire) in a proximal direction through the insertion tube 25. Releasing the actuator 46 allows the expandable assembly 40 to collapse back into its collapsed state.

In another embodiment, the ridges 44 are fabricated such that the steady state of the expandable assembly 40 is the expanded state of fig. 3B. In this case, the expandable assembly 40 is open outwardly to an expanded state as it is pushed out of the sheath, and the actuator 46 may be replaced by a flexible push rod for straightening the ridge 44 prior to retracting the expandable assembly into the sheath.

Reference is now made to fig. 4-6, 7A and 7B, which schematically illustrate a method for preparing a sheath 60 of a catheter expandable assembly, in accordance with an embodiment of the present invention. Fig. 4 is a flow chart showing steps in the method, while fig. 5 is a schematic side view of a system 80 for preparing a sheath. Fig. 6 is a schematic side view of a braided tube 100 prepared using the system of fig. 5.

As an initial step, at a fiber selection step 170, the diameter of the fibers 88 to be used to make the sheath and the size of the holes to be formed in the sheath are selected. For example, PET or nylon fibers of about 25 denier to 100 denier may be used, and the holes in the sheath may have an area of from about 10 μm ² to about 100,000 μm ², as described above. If desired, a hydrophilic or hydrophobic coating may be applied to the fibers at the coating step 172.

At a braiding step 174, the fibers 88 are braided over a suitable mandrel 90 to form a tube 100 having a varying diameter. As shown in fig. 5, the mandrel 90 includes a plurality of bulbous protrusions 84 disposed along the shaft 82. The bulbous protrusion 84 may be a balloon member that is inflated to a desired shape such that it serves as a woven potential support structure for the fibers 88. Braiding machine 86 braids fibers 88 on a mandrel 90, as is known in the art. As shown in fig. 6, the resulting tube 100 includes a bulb 102 of the desired size with a narrower neck 104 between the bulbs. The bulbous object 102 is sized to fit over the basket assembly 40, while the neck 104 fits snugly over the distal end of the insertion tube 25 (as shown in fig. 2). The knitting parameters of knitting machine 86 are set such that bulbous object 102 includes openings or apertures 103 of a desired size (e.g., aperture or aperture area). To ensure firm contact between the braided outer cover 60 and the inflatable assembly 40, the braided outer cover 60 may be sized slightly smaller than the inflatable assembly 40. For example, each bulbous object 84 (defining the inner diameter of the outer cover 60) may be sized such that the maximum outer diameter of the bulbous protrusion 84 of the mandrel 90 (which is also the maximum inner diameter ID of the bulbous object 102) is about 5% to 20% less than the maximum outer diameter OD of the inflatable assembly 40 or 40' (fig. 7A and 7B). The maximum outer diameter OD of the expandable assembly 40 may be measured from the radially outermost point of the expandable assembly (e.g., from one electrode to the diametrically opposite electrode (fig. 7A), or from one ridge to the diametrically opposite ridge).

At a sheath separation step 176, the neck 104 in the tube 100 is cut to separate the tube 100 into individual pluralities of bulbs 102, which may now be considered the sheath 60. It should be noted that the underlying balloon or balloon member 84 of the mandrel 90 is deflated and withdrawn through the tube 100 prior to separating the balloon 102 into separate members or sheaths 60. Alternatively, after separating the balloon 102 into separate pieces, the underlying balloon or balloon member 84 may also be retracted at this stage. As previously described, after cutting the distal ends of the bulb 102, the loose ends of the fibers 88 are closed by fastening the ends together with an adhesive, fusing the ends together, or any other suitable sealing method. The sheath 60 (the precursor being the bulb 102) is then assembled over the basket assembly 40 or 40' by compressing the expandable assembly 40 (fig. 7A) or the vent assembly 40' (fig. 7B) such that the assembly 40 or 40' will fit within the smaller tubular member (e.g., neck 104) of the connection sheath 60.

In the embodiment of fig. 7B, the inflatable assembly 40' is in the form of a balloon membrane 70 coupled to the distal end of the tubular shaft 25. A plurality of electrodes 54' may be disposed on respective substrates 55 disposed on the outer surface of the membrane 70. The conductive members 72 may be used to deliver electrical energy to the respective electrodes 54'. The conductive member 72 may be provided inside or outside the film 70 in the form of an electrical trace. Alternatively, the conductive member 72 may be a wire disposed within the interior volume defined by the balloon membrane 70. The conductive member 72 may extend through the insertion tube 25 up to the ablation generator. Irrigation holes 74 extend through balloon membrane 70 to allow irrigation fluid delivered from insertion tube 25 to flow through membrane 70 and through holes 103 of porous outer cover 60. The actuator 46 may be mounted inside the membrane 70 (and shown in phantom) such that the actuator is fixed to the distal hub 48 and allows the hub 48 to be extended relative to the insertion tube 25 (i.e., compress the membrane 70 into a smaller outer profile) or the hub 48 to be retracted relative to the insertion tube 25 (i.e., expand the membrane 70 into a larger profile). Membrane 70 is preferably made of a more flexible material than porous covering 60.

Assembly of the expandable member 40 'may be accomplished by venting the membrane 70 and inserting the member 40' into a smaller tube (e.g., neck 104) of the sheath 60. Thereafter, the member 40' may be expanded and the ends of the sheath 60 may be joined to the proximal and distal ends of the membrane 70. Details of embodiments of the expandable member 40' may be understood with reference to U.S. patent application Ser. No. 16/707,175 (BIO 6195USNP 1) (published as U.S. patent publication 2021/0169567A 1), filed 12/9, 2019, which is incorporated herein by reference as if set forth herein.

It should be understood that the above embodiments are cited by way of example, and that the present invention is not limited to what has been particularly shown and described hereinabove. Rather, the scope of the present invention includes both combinations and sub-combinations of the various features described hereinabove as well as variations and modifications thereof which would occur to persons skilled in the art upon reading the foregoing description and which are not disclosed in the prior art.

Claims (20)

1. A medical device, comprising:

An insertion tube configured for insertion into a body cavity of a patient;

An expandable assembly distally connected to the insertion tube and comprising an electrode configured to apply electrical energy to tissue within the body lumen; and

A flexible porous sheath mounted on the inflatable assembly and configured to contact both the tissue and the electrode within the body lumen such that the electrical energy is applied from the electrode to the tissue through the sheath.

2. The apparatus of claim 1, wherein the sheath comprises expanded polytetrafluoroethylene (ePTFE).

3. The apparatus of claim 1, wherein the sheath comprises braided polymer fibers.

4. The apparatus of claim 3, wherein the sheath is woven into a tube having a varying diameter.

5. The apparatus of claim 1, wherein the sheath comprises polymer fibers having a hydrophilic coating.

6. The apparatus of claim 1, wherein the inflatable assembly includes one or more irrigation outlets coupled to deliver irrigation fluid from the insertion tube to the tissue through the sheath.

7. The apparatus of claim 6, wherein the sheath comprises a fabric selected to allow the irrigation fluid to pass from the one or more irrigation outlets through the sheath outwardly to the tissue while preventing blood from penetrating inwardly from the body lumen through the sheath.

8. The apparatus of claim 1, wherein the porous sheath comprises pores having respective areas between 10 μιη ² and 100,000 μιη ².

9. The apparatus of claim 8, wherein the respective areas of the apertures are between 100 μιη ² and 10,000 μιη ².

10. The apparatus of claim 1, wherein the inflatable assembly comprises a plurality of resilient ridges having respective proximal and distal ends, wherein the proximal ends of the ridges are mechanically engaged at a proximal end of the inflatable assembly and the distal ends of the ridges are mechanically engaged at a distal end of the inflatable assembly, and when the inflatable assembly is deployed in the body lumen, the ridges flex radially outward against the sheath, thereby contacting the sheath with the tissue in the body lumen.

11. The apparatus of claim 1, wherein the inflatable assembly comprises:

A balloon membrane comprising a plurality of electrodes disposed radially on an outer surface of the balloon membrane and in contact with a porous outer sheath, each of the plurality of electrodes electrically connected to at least one respective conductive member extending through the insertion tube; and

An irrigation hole extending through the balloon membrane to allow irrigation fluid to flow from the insertion tube through the irrigation hole.

12. A method for preparing a medical device, comprising:

Providing an insertion tube configured for insertion into a body cavity of a patient;

distally connecting an expandable assembly including an electrode to the insertion tube; and

A flexible porous sheath is assembled over the inflatable assembly such that the sheath contacts tissue within the body cavity when the insertion tube is inserted into the body cavity.

13. The method of claim 12, wherein the sheath comprises expanded polytetrafluoroethylene (ePTFE).

14. The method of claim 12, wherein assembling the flexible porous sheath comprises braiding polymer fibers to form the sheath.

15. The method of claim 14, wherein braiding the polymer fibers comprises braiding tubes having varying diameters.

16. The method of claim 14, and comprising applying a hydrophilic coating to the polymer fibers.

17. The method of claim 12, wherein the porous sheath comprises pores having respective areas between 10 μιη ² and 100,000 μιη ².

18. The method of claim 12, and comprising delivering irrigation fluid from the insertion tube through the sheath to the tissue.

19. The method of claim 12, wherein connecting the inflatable assembly includes joining together respective distal ends of a plurality of resilient ridges at a proximal end of the inflatable assembly and joining together respective distal ends of the ridges at a distal end of the inflatable assembly such that when the inflatable assembly is deployed in the body lumen, the ridges flex radially outward, thereby causing the sheath to contact the tissue in the body lumen.

20. The method of claim 12, and comprising coupling an electrical signal generator to apply electrical energy from the electrode through the sheath to the tissue within the body lumen.