CATHETER STEERING MECHANISM
This is a continuation of application Ser. No. 07/976,693 filed on Nov. 13, 1992 now U.S. Pat. No. 5,364,351.
FIELD OF THE INVENTION
The invention generally relates to catheters. In a more specific sense, the invention relates to improved steering mechanisms for catheters that can be steered and manipu- 10 lated within interior regions of the body from a location outside the body.
BACKGROUND OF THE INVENTION
Physicians make widespread use of catheters today in 15 medical procedures to gain access into interior regions of the body. In its important that the physician can control carefully and precisely the movement of the catheter within the body.
The need for careful and precise control over the catheter 2o is especially critical during procedures that ablate tissue within the heart. These procedures, called electrophysiological therapy, are becoming more widespread for treating cardiac rhythm disturbances.
During these procedures, a physician steers a catheter 25 through a main vein or artery (typically the femoral artery) into the interior region of the heart that is to be treated. The physician then further manipulates a steering mechanism to place the electrode carried on the tip of the catheter into direct contact with the tissue that is to be ablated. The 30 physician directs radio frequency energy into the electrode tip to ablate the tissue and form a lesion.
Cardiac ablation especially requires the ability to precisely bend and shape the tip end of the catheter to position the ablation electrode. Previous steering control mechanism 35 have generally applied pulling and pushing forces on a pair of steering wires by winding and unwinding them around a rotatable cam wheel. Such mechanisms have a relatively short life due to metal fatigue occurring in the wires caused by repeated bending and straightening thereof. 40
SUMMARY OF THE INVENTION
The invention provides an improved steering device for manipulating the distal end of a catheter by simultaneously 45 pulling on one of a pair of control wires while not applying tension on the other one of said pair. An important aspect of the invention relates to providing a steering control mechanism that moves the steering wires by applying linear rather than rotary forces on the wires. A related aspect involves 50 minimization of compressive or buckling forces on the wires while applying tension thereto to steer the catheter tip assembly.
Briefly summarized, the invention provides an improved catheter steering mechanism for retracting a first catheter 55 steering wire by applying tension to it while simultaneously allowing a second catheter steering wire to remain static, or at rest and vice versa. The mechanism includes at least one rotatable gear and means, such as a rotatable knob, for manually rotating the gear. A first linearly slidable toothed 60 rack is attached to the proximal end of one steering wire, and a second linearly slidable toothed rack is attached to the proximal end of the other steering wire. A toothed gear rotatable by rotation of the knob engages each of the toothed racks to move them linearly in opposite directions in 65 response to rotation of said gear. Preferably three intermeshing gears are used so that movements of the racks are in the
same direction as the rotation of the knob. Preferably the steering wires are connected to the racks by connections that transfer tension as the racks move away from the wires but allow the wires to be slack when the rack moves toward its associated wire.
In accordance with another aspect of the invention, the knob frictionally engages a housing wherein it is contained so that the wires remain in a selected orientation until moved by further rotation of the knob. Further aspects will be apparent from the following detailed description and accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a perspective view of a catheter that embodies the features of the invention;
FIG. 2 is a top section view of the catheter with fragmentary parts included for illustrative purposes;
FIG. 3 is a side elevational view taken along Line 3—3 of FIG. 2;
FIG. 4 is a top view of the reciprocal racks and guide wire assembly of the catheter; and
FIG. 5 is an exploded view of the drive gear assembly and reciprocal racks for the catheter.
DESCRIPTION OF THE PREFERRED
FIG. 1 shows the assembly of a steerable catheter 10 that embodies the features of the invention. As there shown, the catheter 10 includes three main parts or assemblies: the handle assembly 12, the guide tube assembly 14, and the electrode tip assembly 16.
The catheter 10 can be used in many different environments. This specification will describe the catheter 10 as used to provide electrophysiologic therapy in the interior regions of the heart.
When used for this purpose, a physician grips the handle assembly 12 to steer the guide tube assembly 14 through a main vein or artery, such as the femoral artery, into the interior region of the heart that is to be treated. The physician then further manipulates a steering mechanism 18 on the handle assembly 12 (which will be described later) to place the electrode tip assembly 16 in contact with the tissue that is to be ablated. The physician directs radio frequency energy into the electrode tip assembly 16 to ablate the tissue contacting the electrode tip assembly 16.
As FIGS. 2 and 3 best show, the handle assembly 12 includes a housing 20 that encloses the steering mechanism 18. The steering mechanism 18 includes a rotating toothed gear 22 carried on a shaft 24 within the housing 20. The toothed gear 22 and control knob 26 are attached to shaft 24 by splines 25. Toothed gear 22 is seated for rotation between the upper part 21 and lower part 23 of housing 20. The control knob 26 seats against an O-ring 36, which seals the housing and also provides resistance against movement so that the catheter tip 16 will remain in a selected curved position until a new position is selected by the physician. Internal ribs 27 within knob 26 serve as surfaces for knob 26 to retain O-ring 36.
Movement of the control knob 26 by the user rotates the toothed gear 22 and shaft 24 within the upper housing 21 and the lower housing 23. Clockwise movement of the control knob 26 rotates the toothed gear 22 clockwise, meshed intermediate gear 28 counterclockwise and gear 29 clockwise. Gears 29 and 30 are mounted for rotation together on