Implantable Endocordial Lead With Torque-Transmitting Lanyard

1. Field of the Invention

The present invention relates generally to cardiac stimulation, and more particularly to an implantable endocardial lead which stimulates or senses electrical activity of the heart and which employs a retractable fixation mechanism which can be repeatedly exposed to or shielded from tissue during the process of securing the lead to cardiac tissue.

2. Prior Art

There are generally two types of body implantable leads used with cardiac pacemakers--one which requires surgery to expose the myocardial tissue to which an electrode is affixed and another which can be inserted through a body vessel, such as a vein, into the heart where an electrode contacts the endocardial tissue. In the latter type, the endocardial lead is often secured to the heart through the endothelial lining by a sharpened helix affixed to a distal end of the lead. When the end of the lead contacts the lining of the heart at a desired location, the lead may be secured in place by rotating the lead, thus screwing the helix into the heart tissue.

Such a system has been relatively effective in securing an endocardial lead once the initial location of the lead has been achieved. However, it is known that it is undesirable to expose the sharpened helix while the lead is being inserted through a blood vessel into the heart. Moreover, it is difficult to precisely place an endocardial lead on the first attempt. It is common, therefore, for a physician to repeatedly attempt to place an endocardial lead having a sharpened helix securing means. It is desireable, therefore, to be able to shield the sharpened helix during the insertion of the lead through the vein and between attempts to implant the lead on the heart lining.

In the prior art, various apparatus have been proposed for achieving the desired result. For example, U.S. Pat. No. 3,974,834 to Lawrence M. Kane, discloses an implantable intervascular lead having an accordion-fold sleeve surrounding a helix. The sleeve is retractable to expose the helix and re-expandable to cover the helix in the event the helix is unscrewed and withdrawn. An object of the invention is to permit the lead to be inserted into and guided through a body vessel without snagging the body vessel.

Another attempt at solving these problems is disclosed in U.S. Pat. No. 4,146,036 to Robert G. Dutcher and Albert S. Benjamin. This patent discloses a body implantable, intervascular lead, having a helix fixation means. Apparatus for shielding the helix comprises a moveable piston or shaft located within the coils of the helix. The shaft is spring-loaded in a retracted position by the action of an elastomeric boot which also serves to seal off body fluids from the interior of the lead. A stylet passes through a lumen in the lead and acts against a proximal end of the shaft to force the shaft forward through the helix thus forming a partial barrier and inhibiting the helix from coming in contact with tissue, at least in the axial direction.

In U.S. Pat. No. 4,649,938 to William A. McArthur, an endocardial lead with an extendible/retractable helix fixation means is described. The helix is mounted on a bobbin carried within the electrode tip. The bobbin and helix are retracted into the electrode tip by the action of a spring and are extended out of the tip by pressure from the end of the stylet inserted through a lumen in the lead.

The present invention provides an implantable endocardial lead with retractable fixation means. It is an improvement to the invention of James I. Bradshaw, assigned to the same Assignee as this invention and disclosed in co-pending U.S. Application which was filed May 16, 1989, entitled IMPLANTABLE ENDOCARDIAL LEAD WITH TORQUE-TRANSMITTING LANYARD. In the preferred embodiment, the fixation means comprises a sharpened helix which can be repeatedly both retracted with an electrode at a distal end of the lead and displaced outside the electrode. The lead defines an lumen from its proximal to its distal end. A lanyard passes through the lumen from the proximal end of the lead to the distal end of the lead, where the lanyard is attached to a sliding member supporting the helix. At the proximal end of the lead, means are provided for moving the lanyard with respect to a longitudinal axis of the lead and for applying a torsional force or torque through the lanyard. When the helix is in an exposed position, torque can be transmitted from the proximal end of the lanyard to the distal end thereof, through the piston and thence to the helix to screw the helix into the endocardial tissue. To stiffen the lead during implantation, a stylet can be inserted into a lumen in the lanyard.

It is a principal object of the present invention to provide an implantable endocardial lead with retractable fixation means wherein the fixation means can be repeatably shielded and exposed during the implantation process.

A further object of the invention is to provide a lead wherein the fixation means is selectively shielded within an electrode located at the distal end of the lead and wherein the fixation means is selectively exposed and shielded by the action of a lanyard.

Another object of the invention is to provide an implantable endocardial lead with capable of turning a retractable fixation means which can be repeatedly exposed and shielded by the action of an lanyard.

Another important object of the invention is to provide means for controlling the displacement of the lanyard during implantation of the lead.

These and other objects and features of the present invention will be apparent from the detailed description taken with reference to the accompanying drawings.

FIG. 1 is a prospective view of an implantable endocardial lead and a jig for controlling the displacement of a lanyard according to the present invention;

FIG. 2 is a sectional view of the jig for controlling the displacement of the lanyard taken along line 2--2 of FIG. 1;

FIG. 3 is an additional cross sectional view of the jig of FIG. 2, showing a cross section of a plunger; and

FIG. 4 is an enlarged cross sectional view of the plunger of FIG. 3; and

FIG. 5 is a cross section of a distal end of the lead of FIG. 1 taken along lines 4--4.

Reference is now made to the drawings, wherein like numerals designate like parts throughout. FIG. 1 shows an assembly, generally designated 10, comprising an endocardial lead 12 and a jig 14. A wing-nut 16 secures a proximal end 18 of the lead 12 in the jig 14. The lead 12 has a suture sleeve 20 which slides along the lead 12 and which can be attached at an entrance into a vein of a patient in a conventional manner. The lead 12 also has an electrode 22 located at a distal end 24 of the lead.

As shown in FIG. 5, the lead 12 comprises a silicon or polyurethane sheath 26 which defines a lumen 28 along a longitudinal axis of the lead 12. Within the lumen 28, there is a coil conductor 30 for transmitting electrical impulses between the electrode 22 and the proximal end 18 of the lead 12. In the illustrated embodiment, a trifilar conductor is shown as the coil conductor 30. The coil conductor 30 wraps around a crimp slug 32 at the distal end 24 of the lead 12.

The electrode 22 comprises a ring contact 34 and a conductive sleeve 36. The conductive sleeve 36 fits over the crimp slug 32 and the coil conductor 30 and the three elements just mentioned are secured together by a crimp 38 in the conductive sleeve 36. The silicon sheath 26 encloses the conductive sleeve 36 of the electrode 22 to the ring contact 34.

In the illustrated embodiment, a fixation means is illustrated by a sharpened helix 40. A sliding member 42 supports the helix 40 in relatively constant alignment along the longitudinal axis of the lead 12. The piston 42 comprises a sliding member which slidably engages the conductive sleeve 36. On the distal side of the piston 44, the sliding member 44 forms an cylindrical male member 46 which slidably engages an cylindrical female member 48 in the electrode 22. The cylindrical shape of the two members 46, 48 permits the male member 46 to rotate when torque is transmitted as hereinafter described screw the helix 40 into the endocardial tissue of the patient.

A lanyard 54 passes through the lumen 28 in the lead 12 from the proximal end 18 to the distal end 24 thereof. In the preferred embodiment, the lumen 54 is composed of a material such as polyamide which is relatively incompressible and inextensable but flexible so that both pushing and pulling forces and torsional forces can be transmitted from the jig 14 to the sliding member 42 through the lanyard 54. The lanyard 54 is hollow so that a stylet 56 can be inserted through the lanyard 54 to stiffen the lead 12 during insertion in the body of the patient. The lanyard 54 passes slidably through the center of the crimp slug 32 and is adhesively secured to the piston 44 by epoxy filler 50.

At the proximal end 18 of the lead 12, the lanyard 54 is secured to the jig 14, as shown in FIG. 2. The jig 14 comprises a jig body 56. The wing-nut 16 clamps the proximal end 18 of the lead 12 into the jig body 56. Apertures 58 and 60 are provided so that electrical contact with the lead 12 can be made while the jig 14 is secured to the lead 12. During implantation, electrical signals will be sent through and received from the electrode 22 to verify the accurate positioning of the electrode 22.

The lanyard 54 passes through the body 56 of the jig 14 and into a plunger 62. As seen in FIGS. 3 and 4, the lanyard 54 is adhesively secured at a distal end of a bore 64 in a hexagonal piston 66. The hexagonal piston 66 slides axially within an hexagonal chamber 62. Because of the corresponding shapes of the piston 66 and the chamber 67 torque can be transmitted from the plunger 62 to the lanyard 54. To provide adhesion, epoxy filler 68 may be injected into an aperture 65 in the hexagonal piston 66. In a central portion of the hexagonal piston 66, the bore 64 is reduced in diameter to form an insertion funnel 72. A polyamide tube 74 is secured to the plunger 62 by an adhesive bead 76 at the proximal end of the polyamide tube 74. The distal end of the polyamide tube 74 slides within the bore 64. A spring 77 pushes the hexagonal piston 66 toward the distal end of the plunger 62. The pushing action of the spring 77 is transmitted by the hexagonal piston 66 to the lanyard 54. A second insertion funnel 78 is provided at the proximal end of the plunger 62. The insertion funnels 72, 78 and the polyamide tube 74 aide a physician in inserting the stylet 56 into the bore 64 and through the lanyard 54 to the distal end of the lead 12.

To facilitate movement of the plunger 62, the proximal end of the plunger is provided with a knob 80. The plunger 62 also has first and second circumferential notches 82, 84. Opposing clips 86, 88 selectively engage the notches 82, 84 to hold the plunger 62 in one of two selectable positions. In the first position, shown in FIGS. 3 and 4, the clips 86, 88 engage the first circumferential notch 82 so that the lanyard 54 is placed in tension and the helix 40 is withdrawn within the electrode 22. In the second position, shown in FIG. 2, the clips 86, 88 engage the second circumferential notch 84 so that the lanyard 54 is placed in compression by the spring 76 and the sharpened helix 40 can be exposed outside of the electrode 22.

When the distal end 24 of the lead 12 has been inserted to an appropriate location inside the body of the patient, an attending physician can use the body 56 of the jig 14 to hold the lead 12 and prevent turning of the lead 12. The plunger 62 is thrust into the second position where the clips 86, 88 engage the second circumferential notch 84. By action of the spring 76 the helix 40 is pressed against any tissue abutting the tip electrode 22. By twisting the knob 80, the plunger 62 can be rotated inside the body 56 of the jig 14. This rotational motion is transmitted through the hexagonal piston 66 to the lanyard 54 and thence to the piston 42 which supports the helix 40. Turning the helix 40 acts to screw the helix into adjacent tissue or to unscrew it, depending on the direction of rotation. The small diameter and wall thickness of the lanyard 54 when compared with the lead 12 implies that the transmission of equivalent torque through the lanyard 54 rather than through the lead 12 produces much higher stress concentrations. Nevertherless, I have found that a polyamide lanyard can sustain the stresses necessary to transmit an appropriate level of torque for screwing the helix into tissue. Among other advantages, this tends to reduce the tendency of the lead 12 to move when torque is applied through it, which can result in movement of the electrode 22 away from desired fixation site in the patient's body.

During implantation, the sharpened helix 40 can be repeatedly moved into and out of the electrode 22 until proper placement has been achieved. Then the physician can withdraw the stylet 68 and sever the lanyard 54 with a scalpel placed in a scalpl slot 90 in the jig 14. The wing-screw 16 can then be loosened and the jig 14 removed from the proximal end 18 of the lead 12. The proximal end of the lead 12 can then be inserted into an appropriate medical device, such as an implantable cardiac pacemaker.

The invention may be embodied in other specific forms without departing from the spirit or essential characteristics thereof. The present embodiment is therefore considered in all aspects as illustrative and not restrictive, the scope of the invention being indicated by the appended claims rather than by the foregoing description, and all changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein.