Patent Publication Number: US-2023138104-A1

Title: Basket catheter with porous sheath

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims benefit of priority to prior filed U.S. Provisional Patent Application No. 63/274,334 filed on Nov. 1, 2021 which is hereby incorporated by reference as set forth in full herein. 
    
    
     FIELD 
     The present invention relates generally to invasive medical equipment, and particularly to apparatus for ablating tissue within the body and methods for producing and using such apparatus. 
     BACKGROUND 
     Cardiac arrythmias are commonly treated by ablation of myocardial tissue in order to block arrhythmogenic electrical pathways. For this purpose, a catheter is inserted through the patient&#39;s vascular system into a chamber of the heart, and an electrode or electrodes at the distal end of the catheter are brought into contact with the tissue that is to be ablated. In some cases, high-power radio-frequency (RF) electrical energy is applied to the electrodes in order to ablate the tissue thermally. Alternatively, high-voltage pulses may be applied to the electrodes in order to ablate the tissue by irreversible electroporation (IRE). 
     Some ablation procedures use basket catheters, in which multiple electrodes are arrayed along the spines of an expandable assembly at the distal end of the catheter. The spines bend outward to form a basket-like shape and contact tissue within a body cavity. For example, U.S. Patent Application Publication 2020/0289197 describes devices and methods for electroporation ablation therapy, with the device including a set of spines coupled to a catheter for medical ablation therapy. Each spine of the set of spines may include a set of electrodes formed on that spine. The set of spines may be configured for translation to transition between a first configuration and a second configuration. 
     SUMMARY 
     Embodiments of the present invention that are described hereinbelow provide improved apparatus for ablating tissue with the body, as well as methods for producing and using such apparatus. 
     There is therefore provided, in accordance with an embodiment of the invention, medical apparatus, including an insertion tube configured for insertion into a body cavity of a patient and an expandable assembly connected distally to the insertion tube and including electrodes, which are configured to apply electrical energy to tissue within the body cavity. A flexible porous sheath is fitted over the expandable assembly and configured to contact the tissue within the body cavity so that the electrical energy is applied from the electrodes through the sheath to the tissue. 
     There is also provided, in accordance with an embodiment of the invention, a method for producing a medical device, which includes providing an insertion tube configured for insertion into a body cavity of a patient, and connecting distally to the insertion tube an expandable assembly including electrodes. A flexible porous sheath is fitted over the expandable assembly so that the sheath contacts tissue within the body cavity when the insertion tube is inserted into the body cavity. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above and further aspects of this invention are further discussed with reference to the following description in conjunction with the accompanying drawings, in which like numerals indicate like structural elements and features in various figures. The drawings are not necessarily to scale, emphasis instead being placed upon illustrating principles of the invention. The figures depict one or more implementations of the inventive devices, by way of example only, not by way of limitation. 
         FIG.  1    is a schematic pictorial illustration showing a system for cardiac ablation, in accordance with an embodiment of the invention; 
         FIG.  2    is a schematic side view of a catheter expandable assembly with a porous sheath, in accordance with an embodiment of the invention; 
         FIGS.  3 A and  3 B  are schematic cutaway views of the catheter expandable assembly of  FIG.  2    in collapsed and expanded configurations, respectively, in accordance with an embodiment of the invention; 
         FIG.  4    is a flow chart that schematically illustrates a method for producing a sheath for a catheter expandable assembly, in accordance with an embodiment of the invention; 
         FIG.  5    is a schematic side view of a system for producing sheaths for catheter basket assemblies, in accordance with an embodiment of the invention; 
         FIG.  6    is a schematic side view of a braided tube produced using the system of  FIG.  5   , in accordance with an embodiment of the invention; 
         FIG.  7 A  is a side view of an exemplary expandable member that can be used with the braided outer cover of  FIG.  6   , in accordance with an embodiment of the invention; and 
         FIG.  7 B  is a side view of yet another expandable member that can be used with the braided outer cover of  FIG.  6   , in accordance with an embodiment of the invention. 
     
    
    
     DETAILED DESCRIPTION 
     As used herein, the terms “about” or “approximately” for any numerical values or ranges indicate a suitable dimensional tolerance that allows the part or collection of components to function for its intended purpose as described herein. More specifically, “about” or “approximately” may refer to the range of values ±10% of the recited value, e.g. “about 90%” may refer to the 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 systems or methods to human use, although use of the subject invention in a human patient represents a preferred embodiment. As well, the term “proximal” indicates a location closer to the operator whereas “distal” indicates a location further away to the operator or physician. 
     When used herein, the terms “tubular” and “tube” are to be construed broadly and are not limited to a structure that is a right cylinder or strictly circumferential in cross-section or of a uniform cross-section throughout its length. For example, the tubular structure or system is generally illustrated as a substantially right cylindrical structure. However, the tubular system may have a tapered or curved outer surface without departing from the scope of the present invention. 
     Basket catheters are useful in performing ablation procedures rapidly and efficiently, because the spines of the basket catheter (and thus the electrodes on the spines) are able to contact and ablate the tissue at multiple locations concurrently. The spines themselves, however, can give rise to dangerous blood clots during the ablation procedure, due to the disturbance they cause in the blood flow, as well as due to arcing between the spines, particularly in IRE-based ablation. Furthermore, a spine can become embedded in the tissue during the procedure, which can lead to local overheating, resulting in charring and/or other trauma. The use of spines having smooth, rounded profiles can be helpful in mitigating these effects, but by itself does not eliminate the problems of clotting and tissue damage. 
     Embodiments of the present invention that are described herein address these problems by covering the expandable assembly with a porous sheath. As used herein, the term “sheath” is intended to include “an outer cover” or a “membrane”. The sheath prevents direct contact between the spines and the tissue, while still permitting electrical energy to be applied from the electrodes through the sheath to the tissue. The type of material and thickness of the sheath may be chosen so that irrigation fluid delivered through the catheter to the expandable assembly can pass outward through the sheath to the tissue, while still preventing blood from penetrating inward through the sheath from the body cavity. The sheath is thus useful in preventing both clotting and tissue damage. 
     Based on these principles, the disclosed embodiments provide medical apparatus comprising an insertion tube for insertion into a body cavity of a patient and an expandable assembly connected distally to the insertion tube. A flexible porous sheath is fitted over the expandable assembly so that the sheath contacts the tissue within the body cavity. The expandable assembly comprises electrodes, which apply electrical energy through the sheath to tissue within the body cavity. Although the embodiments that are described hereinbelow relate specifically to a basket catheter for intracardiac ablation, the principles of the present invention may be adapted for use in other sorts of procedures in which electrical energy is applied to biological tissues. 
     In some embodiments, an electrical signal generator applies electrical energy to the electrodes on the expandable assembly with an amplitude sufficient to ablate the tissue contacted by the spines. In one embodiment, the electrical signal generator applies bipolar electrical pulses to the electrodes with an amplitude sufficient so that the electrical energy applied from the electrodes 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 electrodes with a power sufficient so that the electrical energy applied from the electrodes through the sheath causes thermal ablation of the tissue. 
       FIG.  1    is a schematic pictorial illustration of a system  20  used in an ablation procedure, in accordance with an embodiment of the invention. Elements of system  20  may be based on components of the CARTO® system, produced by Biosense Webster, Inc. (Irvine, California). 
     A physician  30  navigates a catheter  22  through the vascular system of a patient  28  into a chamber of a heart  26  of the patient, and then deploys an expandable assembly  40  (or  40 ′), over which a flexible porous sheath is fitted (as shown in detail in  FIG.  2   ,  FIG.  3 A , and  FIG.  3 B ), at the distal end of the catheter  22 . The proximal end of expandable assembly  40  (or  40 ′) is connected to the distal end of an insertion tube  25 , which physician  30  steers using a manipulator  32  near the proximal end of catheter  22 . Expandable assembly  40  is inserted in a collapsed configuration through a tubular delivery sheath  23 , which passes through the vascular system of patient  28  into the heart chamber where the ablation procedure is to be performed. Once inserted into the heart chamber, 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 a control console  24 . A display  27  on console  24  may present a map  31  or other image of the heart chamber with an icon showing the location of expandable assembly  40  (or  40 ′) in order to assist physician  30  in positioning the expandable assembly at the target location for the ablation procedure. 
     Once expandable assembly  40  (or  40 ′) is properly deployed and positioned in heart  26 , physician  30  actuates an electrical signal generator  38  in console  24  to apply electrical energy (such as IRE pulses or RF waveforms) to the electrodes on the expandable assembly, under the control of a processor  36 . The electrical energy may be applied in a bipolar mode, between pairs of the electrodes on expandable assembly  40  (or  40 ′), or in a unipolar mode, between the electrodes on expandable assembly  40  (or  40 ′) and a separate common electrode, for example a conductive back patch  41 , which is applied to the patient&#39;s skin. During the ablation procedure, an irrigation pump  34  delivers an irrigation fluid, such as saline solution, through insertion tube  25  to expandable assembly  40  (or  40 ′). 
     Typically, catheter  22  comprises one or more position sensors (not shown in the figures), which output position signals that are indicative of the position (location and orientation) of expandable assembly  40  (or  40 ′). For example, expandable assembly  40  (or  40 ′) may incorporates one or more magnetic sensors, which output electrical signals in response to an applied magnetic field. Processor  36  receives and processes the signals in order to find the location and orientation coordinates of expandable assembly  40  (or  40 ′), using techniques that are known in the art and are implemented, for example, in the above-mentioned Carto system. Alternatively or additionally, system  20  may apply other position-sensing technologies in order to find the coordinates of expandable assembly  40  (or  40 ′). For example, processor  36  may sense the impedances between the electrodes on expandable assembly  40  (or  40 ′) and body-surface electrodes  39 , which are applied to the chest of patient  28 , and may convert the impedances into location coordinates using techniques that are likewise known in the art. In any case, processor  36  uses the coordinates in displaying the location of expandable assembly  40  (or  40 ′) on map  31 . 
     Alternatively, catheter  22  and the ablation techniques that are described herein may be used without the benefit of position sensing. In such embodiments, for example, fluoroscopy and/or other imaging techniques may be used to ascertain the location of expandable assembly  40  (or  40 ′) in heart  26 . 
     The system configuration that is shown in  FIG.  1    is presented by way of example for conceptual clarity in understanding the operation of embodiments of the present invention. For the sake of simplicity,  FIG.  1    shows only the elements of system  20  that are specifically related to expandable assembly  40  and ablation procedures using the expandable assembly. As used herein, the term “expandable assembly” includes either of the assembly  40  ( FIGS.  2 ,  3 A,  3 B, and  7 A ) or  40 ′ ( FIG.  7 B ). The remaining elements of the system will be apparent to those skilled in the art, who will likewise understand that the principles of the present invention may be implemented in other medical therapeutic systems, using other components. All such alternative implementations are considered to be within the scope of the present invention. 
     Reference is now made to  FIGS.  2 ,  3 A and  3 B , which schematically show details of expandable assembly  40 , which is covered by a flexible, outer covering or porous sheath  60  in accordance with an embodiment of the invention.  FIG.  2    is a side view of expandable assembly  40  in its expanded state, while  FIGS.  3 A and  3 B  are cutaway views showing the expandable assembly  40  in collapsed and expanded states (with outer covering  60 ), respectively. 
     Expandable assembly  40  has a distal end  48  and a proximal end  50 , which is connected to a distal end  52  of insertion tube  25 . The expandable assembly comprises multiple spines  44 , whose proximal ends are conjoined at proximal end  50 , and whose distal ends are conjoined at distal end  48 . One or more electrodes  54  are disposed externally on each of spines  44 . Alternatively, spines  44  may comprise a solid conducting material and may thus serve as electrodes themselves, for example as described in U.S. patent application Ser. No. 16/842,648 (BIO6265USNP1) filed Apr. 7, 2020, published as U.S. Patent Publication 2021/0307815A1 whose disclosure is incorporated herein by reference. 
     Irrigation outlets  56  in spines  44  allow irrigation fluid flowing within the spines  44  to exit and irrigate tissue in the vicinity of electrodes  54 . Alternatively or additionally, the irrigation outlets may be located elsewhere in the expandable assembly, for example on an irrigation manifold that is contained inside the expandable assembly (not shown in the figures). 
     Sheath  60  is fitted over expandable assembly  40  and thus contacts the tissue in heart  26  when the expandable assembly is expanded and advanced against the tissue. Sheath  60  prevents direct contact between spines  44  and the heart tissue. Thus, the electrical energy that is applied to electrodes  54  passes through sheath  60  to the tissue. In one embodiment, sheath  60  comprises expanded polytetrafluoroethylene (ePTFE), for example with a thickness of about 70 μm. The ePTFE sheath is advantageous in being lubricious, smooth, strong, and biocompatible and in preventing spines  44  from becoming embedded in the heart tissue. 
     Alternatively, sheath  60  comprises a tube made by braiding suitable polymer fibers, such as a polyethylene terephthalate (PET) or polyamide (nylon) yarn. The tube may be braided with a variable diameter so as to conform better to the deployed basket shape. Specifically, the proximal diameter of the tube may be made to fit the proximal neck of 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, melting the yarn ends together, or any other suitable method of sealing. An advantage of utilizing a fabric in a tubular shape rather than a flat shape is that the material better conforms to the basket shape, and pleats are avoided or minimized. Avoidance of pleats is helpful in reducing the collapsed diameter of sheath  60  and also reduces the potential for blood to coagulate in the folds of the material. A process for production of this sort of braided sheath is described further hereinbelow with reference to  FIGS.  4 - 6   . 
     In yet another embodiment, sheath  60  is made from a sheet of flexible, non-porous material, and pores of the desired size are drilled through the material, for example by laser drilling. In yet a further embodiment the sheath  60  can be formed by blow molding a smaller tubular member to form a balloon membrane with pores subsequently formed through the balloon membrane via laser drilling. 
     The pores in sheath  60  are sufficiently large to permit the irrigation fluid to pass from irrigation outlets  56  outward through sheath  60  to irrigate the heart tissue, while preventing blood from penetrating inward through the sheath from the heart chamber. The inventors have found it advantageous for this purpose that the pores  103  ( FIG.  6   ) in the sheath  60  have pore areas from approximately 10 μm 2  to approximately 100,000 μm 2 . The best results were obtained with pores having areas from approximately 100 μm 2  to approximately 10,000 μm 2 . These ranges of pore areas  103  are also useful in ensuring that irrigation fluid (which is electroconductive) can flow from inside the sheath  60  through the pore areas  103  and outside the porous membrane, sheath  60  to allow the electrical energy from the electrodes  54  to pass freely out through the sheath  60  to the adjoining tissue in order to ablate the tissue. 
     The polymer fibers that are used in producing sheath  60 , such as PET and nylon fibers, are inherently insulators. Both PET and nylon, however, are hygroscopic, and once the fibers absorb water or irrigation fluid, they become more conductive and thus enable the electrical energy output by electrodes  54  to pass more freely through the sheath  60  to the target tissue. To enhance the performance of the sheath  60  in this respect, in one embodiment the polymer fibers are coated with a hydrophilic material. The hydrophilic coating attracts water into the fibers, so that sheath  60  becomes more conductive and thus facilitates 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 the sheath  60  to be pressurized in order for irrigation fluid to flow through it. This positive pressure prevents blood from entering the sheath  60  even when the irrigation is at a low flow rate. 
     In the collapsed state of  FIG.  3 A , spines  44  are straight and aligned parallel to a longitudinal axis  42  of insertion tube  25 , to facilitate insertion of expandable assembly  40  into heart  26 . In this state, sheath  60  collapses inward together with the spines  44 . To ensure that the sheath  60  can collapse with the expandable assembly  40 , the sheath  60  is joined at the distal end  48  and proximal end  50  of the expandable assembly  40 . Upon extension of actuator  46  to separate the distal end  48  and proximal end  50  both the sheath  60  and the spines  44  will compress into a tubular profile of  FIG.  3 A . Upon retraction of actuator towards the proximal end  50 , the spines  44  and the sheath  60  will expand into the spherical like configuration shown in  FIG.  3 B . In the expanded state of  FIG.  3 B , spines  44  bow radially outward, causing sheath  60  to expand and contact tissue within the heart. 
     In one embodiment, spines  44  are produced such that the stable state of expandable assembly  40  is the collapsed state of  FIG.  3 A . In this case, when expandable assembly  40  is pushed out of the sheath, it is expanded by drawing an actuator  46 , such as a suitable wire, in the proximal direction through insertion tube  25 . Releasing actuator  46  allows expandable assembly  40  to collapse back to its collapsed state. 
     In another embodiment, spines  44  are produced such that the stable state of expandable assembly  40  is the expanded state of  FIG.  3 B . In this case, expandable assembly  40  opens out into the expanded stated when it is pushed out of the sheath, and actuator  46  may be replaced by a flexible pusher rod for straightening spines  44  before withdrawing the expandable assembly back into the sheath. 
     Reference is now made to  FIGS.  4 - 6 ,  7 A and  7 B  which schematically illustrate a method for producing sheaths  60  for a catheter expandable assembly, in accordance with an embodiment of the 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 producing the sheaths.  FIG.  6    is a schematic side view of a braided tube  100  produced using the system of  FIG.  5   . 
     As a preliminary step, the diameter of fibers  88  that are to be used in producing the sheaths and the sizes of the pores to be formed in the sheaths are selected, at a fiber selection step  170 . For example, PET or nylon fibers of approximately 25 to 100 denier may be used, and the pores in the sheath may have areas from approximately 10 μm 2  to approximately 100,000 μm 2 , as noted above. If desired, a hydrophilic or hydrophobic coating may be applied to the fibers, at a coating step  172 . 
     Fibers  88  are braided over a suitable mandrel  90  to form a tube  100  having a varying diameter, at a braiding step  174 . As shown in  FIG.  5   , mandrel  90  comprises multiple bulbous protrusions  84  disposed along a shaft  82 . The bulbous protrusion  84  can be a balloon member inflated to a desired shape so that it serves as underlying support structure for the braiding of the fibers  88 . A braiding machine  86 , as is known in the art, braids fibers  88  over mandrel  90 . The resulting tube  100 , as shown in  FIG.  6   , comprises bulbs  102  of the desired size, with narrower necks  104  in between. Bulbs  102  are sized to fit over basket assemblies  40 , while necks  104  fit snugly over the distal end of insertion tube  25  (as shown in  FIG.  2   ). The braiding parameters of braiding machine  86  are set so that bulbs  102  contain openings or pores  103  of the desired size (e.g., pore diameters or pore areas). To ensure firm contact between the braided outer cover  60  and the expandable assembly  40 , the braided outer cover  60  can be sized to be slightly smaller than the expandable assembly  40 . For example, each bulb  84  (defining the inside diameter of outer cover  60 ) can be sized such that the maximum outer diameter of the bulbous protrusions  84  of mandrel  90  (which is also the maximum inside diameter ID of bulb  102 ) is approximately 5% to 20% smaller than the maximum outer OD diameter of the expandable assembly  40  or  40 ′ ( FIG.  7 A and  7 B ). The maximum outside diameter OD of the expandable assembly  40  can be measured from the radially outermost points of the expandable assembly (e.g., from one electrode to diametrically opposed electrode ( FIG.  7 A ) or from one spine to a diametrically opposed spine). 
     Necks  104  in tube  100  are cut to separate the tube  100  into separate multiple bulbs  102 , which can now be considered to be sheaths  60 , at a sheath separation step  176 . It is noted that prior to the separation of bulbs  102  into individual members or sheaths  60 , the underlying balloons or bulbous members  84  of mandrel  90  are deflated and withdrawn through tube  100 . Alternatively, after separation of bulbs  102  into separate pieces, the underlying balloon or bulbous member  84  can also be withdraw at this stage. As noted earlier, the distal ends of bulbs  102  are closed after cutting by fastening together the loose ends of fibers  88  with an adhesive, melting the ends together, or any other suitable method of sealing. The sheaths  60  (formerly bulbs  102 ) are then fitted over basket assemblies  40  or  40 ′ by compressing expandable assembly  40  ( FIG.  7 A ) or deflating assembly  40 ′ ( FIG.  7 B ) so that assembly  40  or  40 ′ will fit within the smaller tubular member connecting the sheath  60  (e.g., neck  104 ). 
     In the embodiment of  FIG.  7 B , the expandable assembly  40 ′ is in the form of a balloon membrane  70  coupled to a distal end of the tubular shaft  25 . A plurality of electrodes  54 ′ can be disposed on respective substrates  55  disposed on the outer surface of the membrane  70 . Conductive members  72  can be used to deliver electrical energy to respective electrodes  54 ′. Conductive members  72  can be disposed inside or outside the membrane  70  in the form of electrical traces. Alternatively, conductive members  72  can be wires disposed within the internal volume defined by balloon membrane  70 . Conductive members  72  can extend through the insertion tube  25  all the way to the ablation generator. Irrigation pores  74  extend through balloon membrane  70  to allow irrigation fluid delivered from insertion tube  25  to flow through membrane  70  and through the pores  103  of the outer porous covering  60 . An actuator  46  can be mounted inside the membrane  70  (and shown as dashed lines) so that actuator is fixed to the distal hub  48  and allow for extension of hub  48  relative to insertion tube  25  (i.e., compressing the membrane  70  into a smaller outer profile) or retraction of hub  48  relative to insertion tube  25  (i.e., causing expansion of membrane  70  into a larger profile). Membrane  70  is preferably made of a less flexible material than porous covering  60 . 
     Assembly of expandable member  40 ′ can be completed by deflating the membrane  70  and inserting the member  40 ′ into the smaller tube (e.g., neck  104 ) of sheath  60 . Thereafter, the member  40 ′ can be inflated and the ends of the sheath  60  can be joined to the proximal and distal end of membrane  70 . Details for an embodiment of the expandable member  40 ′ can be understood with reference to U.S. patent application Ser. No. 16/707,175 (BIO6195USNP1) filed Dec. 9, 2019, published as U.S. Patent Publication 2021/0169567A1 which is hereby incorporated by reference as if set forth herein. 
     It will be appreciated that the embodiments described above 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 subcombinations 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.