AU2013201332B2 - Catheter with bendable tip - Google Patents

Abstract

A medical probe includes a flexible insertion tube, having a distal end for insertion into a body cavity of a patient, and a distal tip, which is disposed at the 5 distal end of the insertion tube and is configured to be brought into contact with tissue in the body cavity. A coupling member couples the distal tip to the distal end of the insertion tube and includes a tubular piece of an elastic material having a helical cut therethrough along a portion of a length of the piece. 06/03/13,document10,2

Description

1 BIOSENSE WEBSTER, INC. AUSTRALIA Patents Act 1990 PATENT SPECIFICATION FOR THE INVENTION ENTITLED "CATHETER WITH BENDABLE TIP" This invention is described in the following statement: M:\Graham\Clare\Speci & Amndmts\20611 Speci.Doc,1, 06/03/13 2 CATHETER WITH BENDABLE TIP CROSS-REFERENCE TO RELATED APPLICATION This application is a divisional of the applicant's Australian Patent 5 Application No. 2005260731 and the whole contents thereof are included herein by reference. FIELD OF THE INVENTION The present invention relates generally to invasive medical devices, and specifically to the construction of probes for insertion into body organs. 10 BACKGROUND OF THE INVENTION In some diagnostic and therapeutic techniques, a catheter is inserted into a chamber of the heart and brought into contact with the inner heart wall. In such procedures, it is generally important that the distal tip of the catheter engages the 15 endocardium with sufficient pressure to ensure good contact. Excessive pressure, however, may cause undesired damage to the heart tissue and even perforation of the heart wall. For example, in intracardiac radio-frequency (RF) ablation, a catheter having 20 an electrode at its distal tip is inserted through the patient's vascular system into a chamber of the heart. The electrode is brought into contact with a site (or sites) on the endocardium, and RF energy is applied through the catheter to the electrode in order to ablate the heart tissue at the site. Proper contact between the electrode and the endocardium during ablation is necessary in order to achieve the desired 25 therapeutic effect without excessive damage to the tissue. A number of patent publications describe catheters with integrated pressure sensors for sensing tissue contact. As one example, U.S. Patent Application Publication 2007/0100332, whose disclosure is incorporated herein by reference, 30 describes systems and methods for assessing electrode-tissue contact for tissue M:\Graham\Clare\Speci & Amndmts\20611 Speci.Doc,2, 06/03/13 3 ablation. An electro-mechanical sensor within the catheter shaft generates electrical signals corresponding to the amount of movement of the electrode within a distal portion of the catheter shaft. An output device receives the electrical signals for assessing a level of contact between the electrode and a tissue. 5 SUMMARY OF THE INVENTION In one aspect, the present invention provides a medical probe, including: a flexible insertion tube, having a distal end for insertion into a body cavity of a patient; 10 a distal tip, which is disposed at the distal end of the insertion tube and is configured to be brought into contact with tissue in the body cavity; and a coupling member, which couples the distal tip to the distal end of the insertion tube and includes a tubular piece of an elastic material having a helical cut therethrough along a portion of a length of the piece, the helical cut subtends an 15 angle between 3600 and 720' about an axis of the tubular piece. In another aspect, the present invention provides a method for producing a medical probe, including: providing a flexible insertion tube, having a distal end which is configured for insertion into a body cavity of a patient, and a distal tip, which is configured to be 20 brought into contact with tissue in the body cavity; and coupling the distal tip to the distal end of the insertion tube using a coupling member, which includes a tubular piece of an elastic material having a helical cut therethrough along a portion of a length of the piece, wherein the helical cut subtends an angle between 360' and 720' about an axis of the tubular piece. 25 In a further aspect, the present invention provides a method for performing a medical procedure, including: inserting into a body cavity of a patient a probe including: a medical probe, including: a flexible insertion tube, having a distal end for insertion into a body cavity 30 of a patient; a distal tip, which is disposed at the distal end of the insertion tube and is configured to be brought into contact with tissue in the body cavity; M:\Graham\Clare\Speci & Amndmts\20611 Speci.Doc,3, 06/03/13 -4 a coupling member, which couples the distal tip to the distal end of the insertion tube and includes a tubular piece of an elastic material having a helical cut therethrough along a portion of a length of the piece, the helical cut subtends an angle between 3600 and 720' about an axis of the tubular piece; and 5 bringing the distal tip into contact with tissue in the body cavity. SUMMARY OF OPTIONAL EMBODIMENTS OF THE INVENTION The embodiments of the present invention that are described hereinbelow 10 provide a novel design of an invasive probe, such as a catheter. In one embodiment the invention provides a medical probe, including a flexible insertion tube, having a distal end for insertion into a body cavity of a patient, a distal tip, which is disposed at the distal end of the insertion tube and is configured to be brought into contact with tissue in the body cavity, a coupling member, which couples the distal tip to the 15 distal end of the insertion tube and includes a tubular piece of an elastic material having a helical cut therethrough along a portion of a length of the piece, the helical cut subtends an angle between 360' and 720' about an axis of the tubular piece; and a position sensor within the distal tip. 20 The coupling member permits the distal tip to bend in response to pressure exerted on the distal tip when the distal tip engages tissue in the body cavity. Typically, the bend angle is proportional to the pressure and may be measured in order to determine the force of contact between the probe and the tissue. On the other hand, the width of the helical cut may be chosen so as to inhibit bending of the 25 distal tip beyond a certain angular limit in order to avoid damaging the probe. There is therefore provided, in accordance with an embodiment of the present invention, a medical probe, including a flexible insertion tube, having a distal end for insertion into a body cavity of a patient, a distal tip, which is disposed at the distal 30 end of the insertion tube and is configured to be brought into contact with tissue in the body cavity; and a coupling member, which couples the distal tip to the distal end 03/10/14,ag 20611 amended speci pages,4 - 4a of the insertion tube and includes a tubular piece of an elastic material having a helical cut therethrough along a portion of a length of the piece. In a disclosed embodiment, the elastic material includes a superelastic alloy, and the 5 helical cut subtends an angle between 3600 and 720' about an axis of the tubular piece. 03/10/14,ag 20611 amended speci pages,4 -5 Typically, the coupling member is configured to bend in response to pressure exerted on the distal tip when the distal tip engages the tissue, and the helical cut has a width chosen so as to inhibit bending of the distal tip beyond a predetermined angular 5 limit. The probe includes a position sensor within the distal tip, wherein the position sensor is configured to sense a position of the distal tip relative to the distal end of the insertion tube, which changes in response to deformation of the coupling member. In a 10 disclosed embodiment, the position sensor is configured to generate a signal in response to a magnetic field, wherein the signal is indicative of a position of the distal tip. The probe may include a magnetic field generator within the distal end of the insertion tube for generating the magnetic field. Additionally or alternatively, the probe includes an electrical conductor, which is coupled to a distal side of the position sensor and is curved 15 to pass in a proximal direction around the position sensor and through the insertion tube so as to convey position signals from the position sensor to a proximal end of the insertion tube. In some embodiments, the probe includes a pull-wire for use by an operator of 20 the probe in steering the probe, wherein the pull-wire passes through the insertion tube and is anchored at a point in the distal end of the insertion tube that is proximal to the helical cut in the coupling member. Alternatively or additionally, the probe includes a heat-resistant plastic sheath covering at least the coupling member. 25 In a disclosed embodiment, the insertion tube, distal tip and coupling member are configured for insertion through a blood vessel into a heart of a patient. There is also provided, in accordance with an embodiment of the present invention, a method for producing a medical probe, including providing a flexible 30 insertion tube, having a distal end which is configured for insertion into a body cavity of a patient, and a distal tip, which is configured to be brought into contact with tissue in the body cavity, coupling the distal tip to the distal end of the insertion tube using a coupling member, which includes a tubular piece of an elastic material having a helical cut therethrough along a portion of a length of the piece, wherein the helical cut subtends 10/06/14,dh-20611 - specipgs4-6 - cdm.docx,5 -6 an angle between 3600 and 720' about an axis of the tubular piece; and inserting a position sensor in the distal tip, coupling an electrical conductor to a distal side of the position sensor; and passing the electrical conductor in a proximal direction around the position sensor and through the insertion tube so as to convey position signals from the 5 position sensor to a proximal end of the insertion tube. In a disclosed embodiment, inserting the probe includes passing the probe through a blood vessel into a heart of the patient, and the method includes ablating the tissue with which the distal tip is in contact. 10 There is additionally provided, in accordance with an embodiment of the present invention, a method for producing a medical probe, including providing a flexible insertion tube, having a distal end for insertion into a body cavity of a patient, and a distal tip, which is configured to be brought into contact with tissue in the body cavity; 15 and coupling the distal dip to the distal end of the insertion tube using a coupling member, which includes a tubular piece of an elastic material having a helical cut therethrough along a portion of a length of the piece. The present invention will be more fully understood from the following detailed 20 description of the embodiments thereof, taken together with the drawings in which: BRIEF DESCRIPTION OF THE DRAWINGS Fig. I is a schematic sectional view of a heart chamber with a catheter in contact with the heart wall inside the chamber, in accordance with an embodiment of the present 25 invention; Fig. 2 is a schematic sectional view of a catheter, in accordance with an embodiment of the present invention; and Fig. 3 is a schematic side view of a coupling member, in accordance with an embodiment of the present invention. 10/06/14,dh-20611 - specipgs4-6 - cdm.docx,6 7 DETAILED DESCRIPTION OF EMBODIMENTS Fig. 1 is a schematic sectional view of a chamber of a heart 22, showing an insertion tube 26 of a catheter 20 inside the heart, in accordance with an embodiment of the present invention. The catheter is typically inserted into the heart 5 percutaneously through a blood vessel, such as the vena cava or the aorta. An electrode 28 on a distal tip 24 of the catheter engages endocardial tissue 30. Pressure exerted by the distal tip against the endocardium deforms the endocardial tissue locally, so that electrode 28 contacts the tissue over a relatively large area. In the pictured example, the electrode engages the endocardium at an angle, rather than 10 head-on. Distal tip 24 therefore bends at an elastic joint 32 relative to the insertion tube of the catheter. The bend facilitates optimal contact between the electrode and the endocardial tissue. Because of the elastic quality of joint 32, the angle of bending of the joint is 15 proportional to the pressure exerted by tissue 30 on distal tip 24 (or equivalently, the pressure exerted by the distal tip on the tissue). Measurement of the bend angle thus gives an indication of this pressure. The pressure indication may be used by the operator of catheter 20 is ensuring that the distal tip is pressing against the endocardium firmly enough to give the desired therapeutic or diagnostic result, but 20 not so hard as to cause undesired tissue damage. U.S. Patent Application 11/868,733, filed October 8, 2007, whose disclosure is incorporated herein by reference, describes a system that uses a pressure-sensing catheter in this manner. Catheter 20 may be used in such a system. 25 Fig. 2 is a schematic, sectional view of catheter 20, showing details of the distal end of the catheter, in accordance with an embodiment of the present invention. A coupling member 40 forms the joint between distal tip 24 and the distal end of insertion tube 26. The coupling member has the form of a tubular piece of an elastic material, with a helical cut along a portion of its length, as shown more 30 particularly in Fig. 3. Typically, the coupling member (along with the distal end of catheter 20 generally) is covered by a flexible plastic sheath 42. When catheter 20 is used, for example, in ablating endocardial tissue by delivering RF electrical energy M:\Graham\Clare\Speci & Amndmts\20611 Speci.Doc,7, 06/03/13 8 through electrode 28, considerable heat is generated in the area of distal tip 24. For this reason, it is desirable that sheath 42 comprise a heat-resistant plastic material, such as polyurethane, whose shape and elasticity are not substantially affected by exposure to the heat. 5 Catheter 20 includes a position sensor 44 within distal tip 24. (In the pictured embodiment, the position sensor is contained within a part of coupling member 40 that is inside the distal tip of the catheter.) The position sensor is connected via a conductor 46 to a processing unit (not shown) at the proximal end of insertion tube 10 26. Conductor 46 may typically comprise a twisted-pair cable. Position sensor 44 is configured to sense the position of the distal tip relative to the distal end of the insertion tube. As explained above, this position changes in response to deformation of the coupling member, and the processing unit may thus use the position reading in order to give an indication of the pressure exerted on and by the distal tip. 15 For intracardiac operation, insertion tube 26 and distal tip 24 should generally have a very small outer diameter, typically on the order of 2-3 mm. Therefore, all of the internal components of catheter 20, such as conductor 46, are also made as small and thin as possible and are thus susceptible to damage due to even small mechanical 20 strains. To avoid damage to conductor 46 when coupling member 40 bends, the conductor is coupled to the distal side of position sensor 44, as shown in Fig. 2, rather than to the proximal side, from which the path of the conductor would be shorter. The conductor is then curved to pass in a proximal direction around the position sensor and through insertion tube 26 so as to convey position signals from 25 the position sensor to the processing unit via the proximal end of the insertion tube. Position sensor 44 may comprise one or more coils, which are configured to generate signals in response to a magnetic field. These signals are indicative of the position and orientation of distal tip 24. The magnetic field may be produced by a 30 miniature magnetic field generator 48 within the distal end of the insertion tube. Thus, when coupling member 40 bends, the signals generated by the position sensor change and can be analyzed by the processing unit to determine the pressure on the M:\Graham\Clare\Speci & Amndmts\20611 Speci.Doc,8, 06/03/13 9 distal tip. Additional magnetic fields may be generated by field generators (not shown) in fixed locations external to the patient's body. These fields cause position sensor 44 to generate additional signals that are indicative of the position and orientation of distal tip 24 in the fixed frame of reference of the external field 5 generators. These aspects of the operation of position sensor 44 are described in detail in the above-mentioned U.S. Patent Application 11/868,733. They are outside the scope of the present invention. Catheter 20 may comprise a pull-wire 50 for use by an operator in steering 10 the catheter. The pull-wire passes through insertion tube 26 and is anchored at an anchor point 52 in the distal end of the insertion tube. The operator tightens the pull wire (typically by turning a knob - not shown - at the proximal end of the catheter) in order to bend the distal end of the catheter. When the operator releases the pull wire, the catheter straightens due to the resilience of the insertion tube. In catheters 15 that are known in the art, the pull-wire is anchored near the distal tip of the catheter. In catheter 20, however, anchor point 52 is proximal to the helical cut in coupling member 40, and may be proximal to the coupling member altogether, as shown in Fig. 2. This relatively proximal positioning of the anchor point means that the pull wire steers the catheter as a whole, rather than bending the coupling member and 20 distal tip. Fig. 3 is a schematic side view of coupling member 40, in accordance with an embodiment of the present invention. As noted earlier, the coupling member includes a tubular piece 60 of an elastic material, typically a metal material. For 25 example, the coupling member may comprise a superelastic alloy, such as nickel titanium (Nitinol). For intracardiac applications, the Nitinol tube may typically have a length of 10 mm, with outer diameter 2.0 mm and wall thickness 0.05 mm. Alternatively, in other applications, the tube may have larger or smaller dimensions. 30 A helical cut 62 is made along a portion of the length of tubular piece 60, and thus causes the tubular piece to behave like a spring in response to forces exerted on distal tip 24. Cut 62 may be made by laser machining of the tubular piece. For the M:\Graham\Clare\Speci & Amndmts\20611 Speci.Doc,9, 06/03/13 10 tube dimensions given above, cut 62 is typically opened by the laser to a width of about 0.1 mm. To give the appropriate balance between flexibility and stiffness for intracardiac applications, cut 62 typically subtends an angle between 3600 and 7200 about the central axis of the tubular piece, as illustrated in Fig. 3 (in which the cut 5 subtends about 5400). Alternatively, larger or smaller angular extents may be used depending on application requirements. The spring-like behavior of coupling member 40 extends up to a certain angle of bending of tubular piece 60, for example, 300. Above this angle, the sides of cut 10 62 on the inner side of the bend will come into contact, thereby inhibiting any further bending of the distal tip. The width of the cut may thus be chosen so as to impose a predetermined angular limit on the bending of joint 32 (Fig. 1). This sort of bend limit is useful in preventing damage that may occur to the delicate internal components of catheter 20 due to excessive bending. 15 Although the operation and construction of catheter 20 are described above in the context of catheter-based intracardiac procedures, the principles of the present invention may similarly be applied in other therapeutic and diagnostic applications that use invasive probes, both in the heart and in other organs of the body. 20 Furthermore, the principles of the implementation of catheter 20 and coupling member 40 may also be applied to enhance flexibility in catheter designs of other types, such as lasso, helix, and "Pentarray" type catheters. In a helical lasso catheter, for example, resilient elements like coupling member 40 may be incorporated in the helix in order to enhance the ease of use and accuracy of alignment of the lasso in the 25 desired position within the heart. It will thus 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 30 invention includes both combinations and subcombinations of the various features described hereinabove, as well as variations and modifications thereof which would M:\Graham\Clare\Speci & Amndmts\20611 Speci.Doc,10, 06/03/13 11 occur to persons skilled in the art upon reading the foregoing description and which are not disclosed in the prior art. Throughout this specification and the claims which follow, unless the context 5 requires otherwise, the word "comprise", and variations such as "includes" and "including", will be understood to imply the inclusion of a stated integer or step or group of integers or steps but not the exclusion of any other integer or step or group of integers or steps. 10 The reference to any prior art in this specification is not and should not be taken as an acknowledgement or any form of suggestion that the prior art forms part of the common general knowledge. M:\Graham\Clare\Speci & Amndmts\20611 Speci.Doc,11, 06/03/13

Claims (21)

1. A medical probe, including: a flexible insertion tube, having a distal end for insertion into a body cavity 5 of a patient; a distal tip, which is disposed at the distal end of the insertion tube and is configured to be brought into contact with tissue in the body cavity; and a coupling member, which couples the distal tip to the distal end of the insertion tube and includes a tubular piece of an elastic material having a helical cut 10 therethrough along a portion of a length of the piece, the helical cut subtends an angle between 3600 and 720' about an axis of the tubular piece.

2. A medical probe according to claim 1, wherein the elastic material includes a superelastic alloy. 15

3. A medical probe according to either claim 1 or claim 2, wherein the coupling member is configured to bend in response to pressure exerted on the distal tip when the distal tip engages the tissue, and wherein the helical cut has a width chosen so as to inhibit bending of the distal tip beyond a predetermined angular limit. 20

4. A medical probe according to any one of claims 1 to 3, further including a position sensor within the distal tip.

5. A medical probe according to claim 4, wherein the position sensor is 25 configured to sense a position of the distal tip relative to the distal end of the insertion tube, which changes in response to deformation of the coupling member.

6. A medical probe according to either claim 4 or claim 5, wherein the position sensor is configured to generate a signal in response to a magnetic field, and wherein 30 the signal is indicative of a position of the distal tip. 03/10/14,ag 20611 amended speci pages,12 - 13

7. A medical probe according to claim 6, further including a magnetic field generator within the distal end of the insertion tube for generating the magnetic field.

8. A medical probe according to any one of claims 4 to 7, further including an 5 electrical conductor, which is coupled to a distal side of the position sensor and is curved to pass in a proximal direction around the position sensor and through the insertion tube so as to convey position signals from the position sensor to a proximal end of the insertion tube. 10

9. A medical probe according to any one of claims 1 to 8, further including a pull-wire for use by an operator of the probe in steering the probe, wherein the pull wire passes through the insertion tube and is anchored at a point in the distal end of the insertion tube that is proximal to the helical cut in the coupling member. 15

10. A medical probe according to any one of claims 1 to 9, further including a heat-resistant plastic sheath covering at least the coupling member.

11. A medical probe according to any one of claims 1 to 10, wherein the insertion tube, distal tip and coupling member are configured for insertion through a 20 blood vessel into a heart of a patient.

12. A method for producing a medical probe, including: providing a flexible insertion tube, having a distal end which is configured for insertion into a body cavity of a patient, and a distal tip, which is configured to be 25 brought into contact with tissue in the body cavity; and coupling the distal tip to the distal end of the insertion tube using a coupling member, which includes a tubular piece of an elastic material having a helical cut therethrough along a portion of a length of the piece, wherein the helical cut subtends an angle between 3600 and 7200 about an axis of the tubular piece. 30

13. A method according to claim 12, wherein the elastic material includes a superelastic alloy. 03/10/14,ag 20611 amended speci pages, 13 - 14

14. A method according to either claim 12 or claim 13, wherein the coupling member is configured to bend in response to pressure exerted on the distal tip when the distal tip engages the tissue, and wherein the helical cut has a width chosen so as 5 to inhibit bending of the distal tip beyond a predetermined angular limit.

15. A method according to any one of claims 12 to 14, further including: inserting a position sensor in the distal tip; coupling an electrical conductor to a distal side of the position sensor; and 10 passing the electrical conductor in a proximal direction around the position sensor and through the insertion tube so as to convey position signals from the position sensor to a proximal end of the insertion tube.

16. A method according to any one of claims 12 to 15, further including 15 inserting a pull-wire through the insertion tube, and anchoring the pull-wire at a point in the distal end of the insertion tube that is proximal to the helical cut in the coupling member.

17. A method according to any one of claims 12 to 16, further including 20 covering at least the coupling member with a heat-resistant plastic sheath.

18. A method for performing a medical procedure, including: inserting into a body cavity of a patient a probe according to any one of claims 1 to 11; and 25 bringing the distal tip into contact with tissue in the body cavity.

19. A medical probe according to claim 1, substantially as herein before described with reference to the accompanying Figures. 30

20. A method for producing a medical probe according to claim 12, substantially as herein before described with reference to the accompanying Figures. 03/10/14,ag 20611 amended speci pages, 14 - 15

21. A method of performing a medical procedure according to claim 18, substantially as herein before described with reference to the accompanying Figures. 5 0 3 /10/14,ag 20611 amended speci pages, 15