Linkage steering mechanism for deflectable catheters

[0001] This application claims priority to U.S. Provisional Patent Application No. 60/582,772, filed Jun. 25, 2004, entitled “Dual Linkage Steering Mechanism for a Deflectable Catheter.

[0002] A rotationally-actuated mechanism having two integral 4-bar linkages is installed in the handle of a deflectable catheter containing at least two mechanical wires, each of which is attached to the mechanism at one end and connected to the catheter's distal tip at the other end. When actuated, the mechanism deflects the distal tip in one direction from the tip's straight position to an arc angle in a plane by pulling one of the wires. The reverse actuation of the mechanism brings the tip back to the straight position while a further reverse actuation deflects the tip in an opposite direction to an arc angle in the same plane by pulling the other wire.

[0003] The mechanism is a function generation linkage whose movable links are made longitudinally proportional to have a variable relative motion ratio, which plays a key role in the functional aspect of the mechanism. A high relative motion ratio of the driven link to the drive link helps achieve a large deflection angle of the distal tip with a very small rotational actuation of the mechanism.

[0004] On either side of the handle is a compliant pad where the drive link member extends out and makes a frictional contact with the pad that holds the link in any position within the mechanism actuation range. The friction-held link maintains the tension in the pull wire deflecting the distal tip and thereby locks the tip curve shape in place. Alternatively, to hold the link for locking a tip-curve shape, on either side of the pin or the integral spindle of the drive link is a complaint washer (with or without a helical spring) that is in a frictional contact between the handle and the link. To have a variable frictional force, one end of the spindle is threaded and inserted into the corresponding threaded hole in the handle.

[0005] Either end of the drive link has an integral plastic component, which acts as a knob for the user to actuate the mechanism to deflect the distal tip. The shape of the handle and the organically-shaped knob including the knob's location on the handle are designed to be ergonomically acceptable.

[0006] Because of their inherent design limitations due to geometric configurations, dimensional constraints, material's mechanical/thermal properties, installed structures/components and fabrication/assembly methods, certain deflectable catheters require 0.5 inch to 1.0 inch of travel of the their pull wires to achieve a distal-tip deflection angle of 270 degrees in one direction for uni-directionally steerable catheter. This means if the steering mechanism has no designed-in mechanical advantage, the actuation distance of the mechanism's actuator (that is often a knob operated by the user) has to be from 0.5 inch to 1.0 inch. But if the catheter's tip is to be deflected in two directions for bi-directionally steerable catheters then the total actuation distance will be from 1.0 inch to 2.0 inches, which is ergonomically not acceptable by the users who often operate the mechanism for several hours with one hand using their thumb.

[0007] So, to address the ergonomic concern, the deflectable catheters that have inherent design limitations are offered with a distal-tip deflection angle of less than 180 degrees for uni-directionally steerable catheters and less than 150 degrees for bi-directionally steerable catheters. These catheters will be acceptable for some clinical procedures, but for other clinical procedures, physicians will still need deflectable catheters, which have a distal-tip deflection angle of 210 to 270 degrees.

[0008] Without changing the catheter shaft design of a deflectable catheter which has inherent design limitations, this dual linkage steering mechanism, attached to the catheter, is able to deflect the catheter's distal-tip to an angle of 270 degrees and even beyond with multiple side linkage.

[0016] To have an ergonomic handle with an ergonomically acceptable rotary steering mechanism which, after attached to a catheter, can deflect the distal tip to 180 degrees and beyond.

[0017] A dual 4-bar linkage steering mechanism consists of four strip/rod-like prismatic or disk/sphere-like revolute side links, called, side link 1A, side link 1B, side link 2A and side link 2B; two strip/rod-like prismatic coupler links, called, coupler link A, coupler link B; and a common fixed link. In one option, the side link 1A and the side link 1B are integrated to act as a whole, and side link 2A and the side link 2B are also integrated to act as a whole. In other option, the side link 1A and the side link 1B are separate and move independently, and the side link 2A and the side link 2B are also separate and move independently. The coupler link A and coupler link B are either rigid or flexible.

[0018] The side link 1A and the side link 1B have three holes each, two of which are utilized to join them to the other links. But the side link 2A, the side link 2B, the coupler link A, the coupler link B and the fixed link have two holes each also for joining them to the other links. Additionally, the side link 1A and the side link 1B both have, as an option, an integral stud or boss that interfaces with the steering wire of a deflectable catheter. The side link 2A and the side link 2B both have a feature, which, at one of their joint holes, extends out in order to interface with and integrate to the other mechanism related parts.

[0019] By using two of its holes, the side link 1A is joined to the coupler link A and the fixed link by pins, rivets or eyelets. Through its third hole, a flexible mechanical cable with a clamp is fed and installed on the side link 1A for one of the steering wires of a deflectable catheter. The side link 2A is joined to the coupler link A and the fixed link also by pins, rivets or eyelets. A knob with ergonomic features is installed on or permanently integrated to the extended end of the side link 2A, leaving a certain amount of the extended portion for interfacing with a frictional pad on a handle.

[0020] Similarly, by using two of its holes, the side link 1B is joined to the coupler link B and the fixed link by pins, rivets or eyelets. Through its third hole, another flexible mechanical cable with a clamp is fed and installed on the side link 1B for the other steering wire of a deflectable catheter. The side link 2B is joined to the coupler link B and the fixed link also by pins, rivets or eyelets. A knob with ergonomic features is installed on the extended end of the side link 2B also, leaving a certain amount of the extended portion for interfacing with another frictional pad on the handle.

[0021] There are, as an option, additional multiple side links joined together in a crossing manner (also, called multiple side linkage) in order to obtain a high travel-output from the linkage steering mechanism. A high travel-output of the steering mechanism results in a large deflection (270 to 360 degree angles) of the distal tip of a deflectable catheter. The high travel-output linkage steering mechanism has certain design variations. Also, to obtain a high travel-output from a lever-type steering mechanism, studs are integrally added to its steering lever, as another option.

[0022] The joint pins, rivets or eyelets for the links are loose fit enough to allow all the movable links to pivot around their joints. The clamp consists of two threaded components which are fastened together to provide a clamping or radial compression force for holding the flexible mechanical cable without causing any slippage.

[0023] In one of the options, the joint between the fixed link and the side link 2A or the side link 2B or both as a whole has a threaded spindle instead of a pin, a rivet or an eyelet. The spindle is permanently integral to the side link and has threads only on its one end.

[0024] It should be noted that functionally, the side link 2A and the side link 2B or both as a whole are also called the drive links, and the side link 1A or the side link 1B or both as a whole, the driven links.

[0025] The linkage steering mechanism is installed in one of the two identical halves of a handle which has two side features where the frictional pads are mounted and a front feature where the proximal end of a deflectable catheter is mounted and the catheter's steering wires extend out. The terminal ends of the steering wires are spliced by a certain means to the flexible mechanical cable that is installed on the side link 1A and the side link 1B or both as a whole. The fixed link of the mechanism is fitted into a certain feature inside the handle half.

[0026] As an option, the handle half has an internal feature with two blind holes, which match the fixed link's joint holes in dimension and location. Using pins, the linkage steering mechanism without the fixed link is installed in the blind holes. The pin of the drive links has a compliant or spring-loaded washer between the boss of the blind hole and the drive link. The blind hole for the drive links is optionally threaded and the mechanism with the threaded spindle is installed with a compliant or spring-loaded washer between the drive link and the boss of the threaded blind hole.

[0027] At each side of the handle half, the driver link's extended portion below the knob is pressed between the frictional pads of the two handle halves when the handle halves are assembled together. The frictional pads provide an enough friction force to hold the drive link at a desired position and also form a seal around the extended portion of the link.

[0028] When the handle halves are assembled together, the compliant or spring-loaded washer compresses between the drive link and the blind-hole boss, exerting an enough friction force to hold the drive link at a desired position. This friction-hold scheme can be used instead of or in addition to the frictional pads on the handle halves. In this option, the compliant or spring-loaded washer over the drive-link pin exerts a constant frictional force throughout the angular travel of the drive link.

[0029] But, in other option, the compliant or spring-loaded washer over the threaded spindle of the drive link exerts a variable frictional force throughout the angular travel of the drive link by virtue of the threaded spindle leading into the threaded blind hole. The more the drive link travels to pull the steering wire, the more the washer compresses to exert increased frictional force. This corresponds to the fact that the more the deflectable catheter's distal tip is deflected, the more the frictional force is needed to hold the drive link of the steering mechanism.