Pacing lead with insertable memory coil

A body implantable lead which may be provided with a desired predetermined curve. A memory coil is inserted into the lead while straightened by a stylet. After removal of the stylet, the memory coil imparts the desired curve to the lead.

BACKGROUND OF THE INVENTION 
This invention relates generally to electrical medical leads and, in 
particular, to cardiac stimulation leads. 
In the field of cardiac pacing, there are available pacemakers designed to 
provide stimulus pulses to and sense the electrical activity of a 
patient's heart. Typically, leads intended for use in the ventricle employ 
an essentially straight lead body which allows location of the electrode 
at the ventricular apex. However, in those applications where the 
electrode is desired to be located in other areas of the heart, such as 
the atrium for A-V sequential pacing or the ventricular septum for his 
bundle monitoring, it is desirable to use a lead which is provided with a 
curve in its distal portion to direct the electrode to its desired 
location within the heart. For example, atrial pacing leads may display a 
J-shaped bend over their distal portion to enable placement of the tip 
electrode in the atrial appendage of the right atrium, or an L-shaped bend 
to facilitate placement of the electrode in the coronary sinus. 
There have been two general approaches to providing a lead with a desired 
bend or curve. The most common approach has been to fabricate the lead in 
such a manner that it tends to assume the desired curve, straightening the 
lead for insertion by means of a stiffening stylet. In these leads, the 
curve facilitates the location of the electrode at the desired location. 
Examples of such leads are discussed in U.S. Pat. No. 3,939,843 issued to 
Smyth, and U.S. Pat. No. 3,729,008 issued to Berkovits and U.S. Pat. No. 
4,332,359 issued to McCorkle. The preset curve of the lead may be also 
straightened by means of a tubular structure such as a needle or a 
catheter, as described in U.S. Pat. No. 3,516,412 issued to Ackerman and 
U.S. Pat. No. 3,866,615 issued to Hewson. As an alternative to providing 
the lead with a preset curve, some leads are adapted to be used with 
stylets which temporarily impart a desired curve to the lead. Examples of 
this technique can be found in U.S. Pat. No. 4,136,703 issued to Wittkampf 
and in commonly assigned U.S. patent application Ser. No. 306,050 by 
Williams for a "Positive Anchoring A-V Lead." 
SUMMARY OF THE INVENTION 
The present invention provides a lead which may be easily provided with a 
desired predetermined curve or bend. As such, the invention allows for a 
pacing lead convertible from use in the ventricle to use in the atrium or 
other desired location. The lead body tends to assume a generally straight 
configuration, typical of prior art ventricular leads and, if used with a 
straight stylet typical of the prior art, it may be used in the ventricle. 
The present invention, however, employs a stylet wire having a generally 
straight configuration, removably mounted within a concentric memory coil 
tending to assume the desired curved shape. The stylet and memory coil may 
be inserted together within the lead body, the stylet maintaining the 
memory coil in a generally straight configuration. After removal of the 
stylet, the memory coil urges the lead body to assume the desired 
predetermined curve, facilitating use of the lead in the atrium. The 
memory coil may extend for the entire length of the lead, or only for a 
portion thereof. 
The many objects, advantages and novel features of the present invention 
will become apparent from the following detailed description of the 
invention when considered in conjunction with the accompanying drawings.

DETAILED DESCRIPTION OF THE DRAWINGS 
FIG. 1 shows a side plan view of a pacing lead according to the present 
invention. Elongated lead body 10 is provided with an insulative sheath 12 
which extends from the distal end of the lead to the proximal end of the 
lead. At the proximal end of the lead is located connector assembly 14, 
which is provided with sealing rings 16, and mounts connector pin 18. 
Slideably mounted around insulative sheath 12 is anchoring sleeve 30. 
Anchoring sleeve 30, insulative sheath 12 and connector assembly 14 may 
conveniently be fabricated of polyurethane or silicone rubber. Connector 
pin 18 may be fabricated of any conductive metal, and is preferably 
fabricated of stainless steel. Tine sheath 26 is located at the distal end 
of lead body 10, and bears four tines 28. Tines 28 are of known design, 
and are fully described in U.S. Pat. No. 3,902,501, issued to Citron et 
al. Mounted at the distal tip of lead body 10 is electrode 24. Electrode 
24 is coupled to connector pin 18 by means of a conductor coil, not 
visible in this drawing. Electrode 24 may conveniently be fabricated of 
platinum or other conductive biocompatible material. Tine sheath 26 may be 
fabricated of silicone rubber, polyurethane or other suitable 
non-conductive material. Visible protruding from connector pin 18 are 
stylet knob 22 and memory coil insertion tool knob 20 (discussed below). 
FIG. 2 illustrates a straightening stylet suitable for use with the present 
invention. Stylet wire 32 is of sufficient length to extend from the 
proximal end to the distal end of the lead illustrated in FIG. 1. At the 
proximal end of stylet wire 32 is located stylet knob 22. Stylet wire 32 
may be conveniently fabricated of stainless steel and knob 22 may be 
fabricated of plastic or other suitable material. 
FIG. 3 shows an insertion tool according to the present invention. The 
insertion tool is comprised of a tubular member 34 which has a 
longitudinal bore running throughout its length. Mounted at the proximal 
end of tubular member 34 is knob 20, which also has a central bore, 
coupled to the bore of tubular member 34. Stylet wire 32 (FIG. 2) is 
insertable through the bores of knob 20 and tubular member 34. When so 
inserted, the distal end of stylet wire 32 protrudes from the distal end 
of tubular member 34 for a significant distance. Tubular member 34 and 
knob 20 may be fabricated of plastic or any other convenient material. 
Alternatively, tubular member 34 may take the form of a coil having a 
central lumen, fabricated of any convenient metal or plastic. 
FIG. 4 illustrates a side plan view of a memory coil appropriate for use 
with the present invention. Memory coil 36 is shown as a monofilar coil 
tending to assume a predetermined bend 38. The length of memory coil 36 
corresponds generally to the distance stylet wire 32 protrudes from the 
distal end of tubular member 34 (FIG. 3) when so inserted. Memory coil 36 
has a diameter approximately equal to that of tubular member 34 (FIG. 3), 
and has a central lumen into which stylet wire 32 (FIG. 2) is insertable. 
When stylet wire 32 is so inserted, memory coil 36 is substantially 
straightened, with the result that curve 38 is not displayed. 
FIG. 5 shows the straightening stylet, memory coil insertion tool, as 
assembled for introduction in to the lead of FIG. 1. In this view, stylet 
wire 32 is seen to straighten memory coil 36. The insertion tool locates 
memory coil 36 distal to tubular member 34. The assembly shown in this 
figure is insertable into the proximal end of the lead shown in FIG. 1, 
through connector pin 18 which is provided with a central bore, 
communicating with the lumen of lead body 10. 
FIG. 6 shows an alternate embodiment of a memory coil according to the 
present invention. Memory coil 40 is substantially longer than memory coil 
36 (FIG. 4) and has sufficient length that when it is inserted in its 
desired location within the lead, a portion of the coil protrudes 
proximally from connector pin 18. Memory coil 40 is provided with a 
central lumen, into which stylet wire 32 (FIG. 2) may be inserted, to 
straighten curve 42. 
FIG. 7 shows memory coil 40 as mounted to the stylet of FIG. 2. As shown, 
stylet wire 32 substantially straightens memory coil 40. The assembly of 
FIG. 7, like the assembly of FIG. 5, is insertable within the lead of FIG. 
1, through the central bore of connector pin 18. 
FIG. 8 shows a cutaway view of the lead of FIG. 1. Visible in this view is 
conductor coil 42, mounted within the lumen of insulative sheath 12. Coil 
conductor 42 extends from electrode 24 (FIG. 1) to connector pin 18 (FIG. 
1). Memory coil 36 and stylet wire 32 are visible inserted within the 
lumen of conductor coil 42. 
In the first embodiment of the present invention, employing the stylet of 
FIG. 2, the insertion tool of FIG. 3 and the memory coil of FIG. 4, the 
method of imparting a desired permanent curve to the lead of FIG. 1 is as 
follows: first, stylet wire 32 is inserted through the central bores of 
knob 20 and tubular member 34. Second, memory coil 36 is slid over the 
distal end of stylet wire 32 until the proximal end of memory coil 36 
contacts the distal end of tubular member 34. This step straightens memory 
coil 36, as illustrated in FIG. 5. Third, the assembled stylet insertion 
tool and memory coil are inserted into the lumen of the lead of FIG. 1. In 
particular, they are inserted through the central bore of connector pin 18 
and advanced through the central lumen of conductor coil 42 until memory 
coil 36 is located at its desired position, typically the distal end of 
the lead. The lead may now be introduced into the atrium of a human heart, 
using standard techniques. Fourth, preferably after introduction of the 
lead into the atrium, the stylet is removed by means of knob 22, while the 
insertion tool is held in place in the lead by holding knob 20 stationary 
relative to connector pin 18. This step allows the lead to display curve 
38 of memory coil 36. Finally, the insertion tool is removed from the lead 
by means of knob 20. 
In the second embodiment of the present invention, employing the stylet of 
FIG. 2 and the memory coil of FIG. 6, the method of imparting a desired 
permanent curve to the lead of FIG. 1 is as follows: First, stylet wire 32 
is inserted in memory coil 36. This step straightens memory coil 36 as 
shown in FIG. 7. Second, the assembled stylet and memory coil are inserted 
into the lumen of the lead of FIG. 1. In particular, they are inserted 
through the central bore of connector pin 18 and advanced through the 
lumen of conductor coil 42 until memory coil 40 is located in its desired 
position. The lead may now be introduced into the atrium using known 
techniques. Fourth, preferably after introduction of the lead into the 
atrium, the stylet is removed by means of knob 22 while memory coil 40 is 
retained within the lead by holding the protruding proximal end of coil 40 
stationary relative to connector pin 18. This step allows the lead to 
display curve 42 of memory coil 40. Finally, that portion of the memory 
coil which protrudes proximal to connector pin 18 is cut off so that the 
lead may be attached to an implantable pulse generator. 
Each of the above discussed embodiments allows for the construction of a 
pacemaker lead convertible between atrial and ventricular applications, 
and capable of displaying any desired preset curve. The first embodiment, 
employing the insertion tool and structural coil of FIG. 4 has as an 
advantage that it allows for a method of insertion which employs no 
cutting steps. The lead produced using this embodiment displays a change 
of flexibility at the proximal end of memory coil 36. In some 
applications, this may be desirable. In other applications, the embodiment 
employing the memory coil of FIG. 6 may be more desirable. The lead 
produced employing this embodiment displays a relatively constant 
flexibility over the length of the lead, due to the fact that memory coil 
40 extends through the entire length of the lead. 
This invention has been described in detail with particular reference to 
preferred embodiments thereof, but it will be understood that variations 
and modifications can be effected within the spirit and the scope of the 
invention.