Spring assembly for catheter

A catheter having a proximal portion and a distal portion terminating in a distal tip, is provided with a spring assembly contained within its distal tip portion for providing a bias against side to side deflection of said distal tip. The assembly preferably includes a central wire having a first diameter, which central wire extends from the proximal portion of the catheter to the distal portion, and a plurality of wires secured to the central wire adjacent the distal end thereof. Each of the wires is stranded together, preferably twisted helically, around the central wire and preferably has a second diameter substantially smaller than the first diameter. Alternatively, the stranded wires can be attached along and parallel to the larger diameter wire, and the latter wire is of a substantially greater length than the stranded wires.

BACKGROUND OF THE INVENTION 
This invention relates to catheters for in vivo insertion into a living 
body and particularly those used for insertion into the cardiovascular 
system for cardiac monitoring and therapy. 
Many catheters require an atraumatic, but constant, tissue contact, for 
example, electro-physiology catheters. However, existing catheters have 
either been soft and atraumatic but sacrifice the ability to provide 
constant tissue contact, or, on the other hand, provide good tissue 
contact but are rigid and, thus, increase the risk of tissue perforations. 
A need has, thus, existed for catheters having the ability to provide a 
firm constant contact with tissues such as cardiac tissues without risk of 
perforation of the tissue. 
SUMMARY OF THE INVENTION 
It is a primary object of the present invention to provide a catheter 
having a novel interior spring configuration that enables the distal tip 
section of a catheter to provide a firm but atraumatic contact with 
tissue. In accordance with a related aspect of the invention, the 
exceptional tissue contact provided by the catheters of the present 
invention provides for improved pacing, sensing of electrical signals and 
recording performance, for example, within the living heart without 
compromising safety. In accordance with a further related aspect, the 
invention provides the dual benefit of maintaining a predictable distal 
tip tissue contact while still achieving a deflectable atraumatic distal 
tip that permits insertion of the catheter without injury to the patient. 
In accordance with a further aspect of the invention, a cable spring 
assembly for a catheter distal tip is provided from a number of individual 
small gauge wires stranded together. In accordance with a further related 
aspect, the stranded wires can be preferably used in connection with a 
single wire of larger diameter. In accordance with yet another aspect of 
the invention, the various wires used in the spring subassembly may be 
provided from different metals such as stainless steel and copper to 
provide springs having preselected stiffness, elasticity and recovery 
rates. In accordance with yet another aspect of the invention, the spring 
assembly is preferably jacketed by means of a polymeric sheath. 
In accordance with a still further aspect of the invention, the spring 
assembly can be provided from wires that have a dual purpose. For example, 
one or more wires can be used as a distal tip anchor (safety) wire and 
other wires can be used as electrode signal wires. 
Briefly, in accordance with one preferred embodiment of the invention, a 
catheter having a proximal portion and a distal portion terminating in a 
distal tip, is provided with a spring assembly contained within its distal 
tip portion for providing a bias against side-to-side deflection of said 
distal tip. The assembly preferably includes a central wire having a first 
diameter, which central wire extends from the proximal portion of the 
catheter to the distal portion, and a plurality of wires secured to the 
central wire adjacent the distal end thereof. Each of the wires is 
stranded together, preferably twisted helically, around the central wire 
and preferably has a second diameter substantially smaller than the first 
diameter. Alternatively, the stranded wires can be attached along and 
parallel to the larger diameter wire, and the latter wire is of a 
substantially greater length than the stranded wires.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
Referring more particularly to the drawings, there is seen in FIG. 1 a 
spring assembly 10 in accordance with the invention. In accordance with 
the illustrated embodiment, assembly 10 includes a relatively larger 
diameter wire formed, for example, from stainless steel 12. Wire 14 would 
generally extend from the proximal end of the catheter to its distal end 
and may be, for example, either an anchor wire or signal wire attached at 
its distal end to a distal end electrode on the catheter. A stranded 
spring assembly 16 is preferably wound around larger diameter wire 12. The 
individual strands 18 of stranded portion 16 may be additional smaller 
diameter stainless steel wires or alternatively could be copper wires in 
the event that less spring force is desired. When more spring force is 
desired a more rigid wire such as Elgiloy (T.M.), a cobalt-chromium-nickel 
alloy is used. The cross-section of individual strands 18 could be 
circular, square or rectangular. It is preferred that the spring 
subassembly be encased in a layer of plastic material 20 which may be PTFE 
or another appropriate plastic material. 
An alternative embodiment of the invention is shown in FIGS. 7-11 wherein 
an alternative subassembly 22 is provided. As best seen in FIGS. 8-10, the 
spring subassembly 22 includes a larger diameter wire 12 secured adjacent 
and parallel to a helically stranded bundle of smaller diameter individual 
wires 18. As seen in FIG. 10, a layer of plastic material 20 can be used 
to encase the subassembly. 
As seen in FIG. 7, the spring subassembly 22 is provided with a curved 
portion as illustrated. This curved portion can be formed by 
simultaneously bending and heating the wire subassembly. Upon cooling the 
subassembly retains a permanent set into the illustrated curve 
configuration. 
A typical installation of spring subassembly 22 into a distal end of a 
catheter 23 is seen in FIG. 11. Catheter distal end 23 includes an end 
electrode 24 secured to the distal extremity thereof. A plurality of ring 
electrodes 26 can be secured concentrically around the body of the 
catheter 23 in the distal end portion for sensing purposes. For example, 
each ring electrode 26 can be attached to a separate electrical lead wire 
28. The lead wires and spring subassembly 22 are all located within the 
lumen of the catheter body 23 as illustrated. Wire 12 can be utilized as 
either an anchor wire for tip electrode 24 or a signal wire or both. 
While preferred embodiments of the invention have been shown for purposes 
of illustration, it will be understood by those skilled in the art that 
numerous modifications can be made falling within the spirit of the 
invention and the scope of the appended claims, including equivalents 
thereof.