Medical electrical lead

An implantable cardioversion/defibrillation lead having an elongated insulative lead body carrying a tip electrode located at its distal end and a cardioversion/defibrillation electrode located on the lead body, proximal to the tip electrode. An elongated conductor coupled to the tip electrode extends proximally within the lead body. At the proximal end of the lead body is a first connector assembly carrying a first connector and a second connector assembly carrying a second connector. An elongated, stranded or cabled conductor is coupled to the cardioversion/defibrillation electrode and to the second connector and extends uninterrupted therebetween. A cylindrical transition member is coupled to the first connector by means of a coiled conductor. A press-fit sleeve having a longitudinal lumen extending therethrough compresses the stranded or conductor between the press-fit sleeve and the transition member to provide electrical interconnection between the stranded or cabled conductor and the transition member.

BACKGROUND OF THE INVENTION 
The present invention relates generally to implantable medical leads and 
more specifically to pacemaker and defibrillation leads employing stranded 
conductors. 
Traditionally, implantable cardiac pacing and defibrillation leads have 
employed monofilar or multifilar coiled conductors, as illustrated in U.S. 
Pat. No. 4,355,646 issued to Kallok et al. More recently, cabled or 
stranded conductors have gained wider acceptance, for example, as 
disclosed in U.S. Pat. No. 5,584,873 issued to Shoberg et al. and 
incorporated herein by reference in its entirety and U.S. Pat. No. 
5,760,341 issued to Laske et al., also incorporated herein by reference in 
its entirety. In conjunction with the use of stranded conductors, new 
mechanisms for interconnecting the conductors to other electrically 
conductive lead components have had to be developed. One such mechanism 
for coupling stranded conductors to electrical components in a lead is a 
press-fit sleeve, as disclosed in U.S. patent application Ser. No. 
08/439,332 for a "Medical Lead With Stranded Conductors", filed May 11, 
1995 by Swoyer et al, also incorporated herein by reference in its 
entirety. 
In the particular context of defibrillation leads, use of the electrodes on 
the leads to sense electrical signals in a bipolar fashion has typically 
been accomplished by one of two ways. The first mechanism for 
accomplishing bipolar sensing is to simply provide a tip electrode and a 
ring electrode, as commonly used in bipolar cardiac pacing leads, for 
example as illustrated in U.S. Pat. No. 4,614,192 issued to Imran et al. 
Alternatively, bipolar sensing can be provided by means of what has come 
to be known as an "integrated bipolar" system, wherein one of the 
defibrillation electrodes on the lead also serves as a sensing electrode, 
in conjunction with the distal or tip electrode on the lead. A lead 
employing an integrated bipolar electrode system is disclosed in U.S. Pat. 
No. 4,603,705 issued to Speicher et al. In such a lead, it is necessary to 
couple the defibrillation electrode which also serves as the sensing 
electrode to separate electrical connectors, so that it may be coupled to 
the input terminal of the sense amplifier on an associated implantable 
cardioverter/defibrillator and to the cardioversion/defibrillation output 
terminal. 
While the lead illustrated in the Speicher patent employs separate 
connector pins for each connection to the pulse generator, it has become 
more common to connect sensing electrodes using a bipolar in-line 
connector conforming to the IS-1 connector standard, typically employed on 
leads intended for use with implantable pacemakers, as disclosed in U.S. 
Pat. No. 5,476,501 issued to Stewart et al., incorporated herein by 
reference in its entirety. In the context of a lead which employs an 
advanceable fixation helix located at its distal end, it is conventional 
to employ a coiled conductor, rotatable within the lead body and coupled 
to a rotatable connector pin extending from the proximal end of the 
connector assembly as the mechanism for rotating the fixation helix, as 
also disclosed in U.S. Pat. No. 5,476,501 issued to Stewart et al. 
SUMMARY OF THE INVENTION 
The present invention is directed toward a cardioversion/defibrillation 
lead which employs integrated bipolar sensing between a tip or distal 
electrode and an adjacent cardioversion electrode. The lead preferably 
employs an IS-1 type in-line bipolar connector assembly and in a preferred 
embodiment of the invention, the lead is provided with an electrode taking 
the form of a rotatable fixation helix, advanced and retracted by means of 
a rotatable, coiled conductor extending to a rotatable connector pin on 
the proximal end of the in-line connector assembly. The defibrillation 
electrode is coupled to a stranded or cabled conductor, which in turn is 
coupled both to a connector ring on the in-line connector assembly and to 
a connector pin on a separate connector assembly for connection to the 
output of the cardioverter/defibrillator. The present invention provides a 
simple, elegant and inexpensive mechanism for providing the required 
interconnection between the various conductors, electrodes and connectors 
described above. 
In particular, the present invention provides for interconnection of the 
stranded conductor coupled to the defibrillation electrode to a coiled 
conductor coupled to an connector, preferably the connector ring on the 
in-line connector assembly. The invention provides a connection mechanism 
which allows the stranded conductor to continue uninterrupted to a 
connector on a separate connector assembly, intended to couple the 
cardioversion/defibrillation pulse generator. The connection is made by 
means of a press-fit sleeve in conjunction with a cylindrical transition 
flange. The transition flange is coupled at its proximal end to the coiled 
conductor and in a preferred embodiment is provided with external 
threading along its distal portion. The press-fit sleeve in a preferred 
embodiment is generally a cylindrical sleeve, located exterior to the 
distal, threaded portion of the transition flange, and compressing the 
stranded or cabled conductor against the outer surface of the transition 
sleeve, providing for mechanical and electrical interconnection of the 
coiled conductor and the stranded conductor. 
The stranded conductor extends proximally from the press-fit sleeve to a 
connector located on a separate connector assembly and extends distally to 
the defibrillation electrode. In a preferred embodiment, the transition 
flange, stranded conductor and press-fit sleeve are assembled by passing 
the insulated stranded conductor through the press-fit sleeve and sliding 
the press-fit sleeve over the distal end of the transition flange, such 
that the threading on the exterior of the transition flange causes flow of 
insulation on the stranded conductor into the spaces between the threads 
on the transition flange, allowing for electrical interconnection without 
the necessity of stripping or removing insulation from the stranded 
conductor. Because the stranded conductor extends uninterrupted from the 
defibrillation electrode to the cardioversion/defibrillation pulse 
generator, a lead construction having a high tensile strength is provided. 
The transition flange is also provided with a longitudinal internal lumen, 
through which a coiled conductor coupled to the tip electrode may pass. 
This construction also allows for the use of a rotatable coiled conductor 
in the preferred embodiment in which the distal or tip electrode takes the 
form of a rotatable helix.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT OF THE INVENTION 
FIG. 1 is a plan view of a lead incorporating a first embodiment of the 
invention. The lead is provided with an elongated insulative lead body 10 
which may be fabricated of polyurethane or silicone rubber or other less 
rigid, elastic, relatively softer biocompatible plastic. The lead body 
carries at its distal end an insulative electrode head 14, which may also 
be fabricated of a relatively more rigid biocompatible plastic, such as a 
polyurethane and which carries an advanceable helical electrode 16. At its 
proximal end, the lead carries a trifurcated connector module 12 
comprising a molded trifurcation sleeve 13, from which three insulative 
tubular sleeves 17, 19 and 23 extend. Sleeve 19 carries a first connector 
assembly which is an IS-1 compatible, in-line connector assembly provided 
with a connector ring 20 coupled to cardioversion/defibrillation electrode 
26, and a connector pin 22 coupled to helical electrode 16. Sleeve 17 
carries a second connector assembly provided with a connector pin 18, also 
coupled to cardioversion/defibrillation electrode 26 by means of a the 
mechanism discussed above. Sleeve 23 carries a third connector assembly 
provided with a connector pin 24, coupled to cardioversion/defibrillation 
electrode 28. 
FIG. 2 is a sectional view of the lead through FIG. 1 in the vicinity of 
the trifurcation sleeve 13, which may be molded of silicone rubber, 
polyurethane or other biocompatible plastic. The proximal portion of the 
lead body 10 terminates within the distal portion of the trifurcation 
sleeve 13 and is an extruded multilumen tube of silicone rubber or other 
biocompatible plastic, including a first lumen enclosing rotatable coiled 
conductor 30 and second and third lumens, not visible in this view, 
enclosing insulated stranded or cabled conductors 40 and 48. Conductor 48 
is provided with an insulative coating, for example a thin layer of 
polytetrafouroethylene and is coupled to cardioversion/defibrillation 
electrode 26 (FIG. 1) and to connector pin 18 (FIG. 1). Conductor 40 is 
coupled to cardioversion/defibrillation electrode 28 (FIG. 1) and to 
connector pin 24 (FIG. 1). Coiled conductor 30 is coupled to the rotatable 
helical electrode 16 (FIG. 1) at the distal end of the lead and to 
rotatable pin 22 (FIG. 1) at the proximal end of the lead. Conductor 48 is 
also coupled to the connector ring 20 (FIG. 1) of the lead by means of 
press-fit sleeve 46 and transition flange 38, which in turn is coupled to 
connector ring 20 (FIG. 1) by means of coiled conductor 44. The 
interconnection of conductors 44 and 48, transition flange 37, and 
press-fit sleeve 46 is discussed in more detail below. 
Coiled conductor 30 is surrounded by insulative sleeves 32 and 36, which 
may be fabricated of silicone rubber, polyurethane or other biocompatible 
plastic, as it extends from the proximal end of lead body 30. Stranded 
conductor 40 is provided with an insulative coating, for example a thin 
layer of polytetrafouroethylene and is further provided with a tubular 
insulative sleeve 34 extending proximally from the proximal end of lead 
body 10. The internal cavity 42 within trifurcation sleeve 13 is 
backfilled with silicone rubber after assembly. Extending proximally from 
the trifurcation sleeve 13 are tubular insulative sleeves 17, 19 and 23, 
which extend to the connector assemblies illustrated in FIG. 1. 
Interconnection of insulated stranded or cabled conductor 48, press-fit 
sleeve 46 and transition flange 38 is accomplished by simply passing the 
insulated conductor 48 through the sleeve 46 and sliding the sleeve 46 
over the distal end of the transition flange 38, causing flow of the 
insulation on conductor 48 into the spaces between the threading on 
transition flange 38 and compressing the stranded conductor between the 
transition flange 38 and the press-fit sleeve 46 to provide an electrical 
and mechanical interconnection. The coiled conductor 44 is simply welded 
to the proximal portion of the transition sleeve in a conventional manner 
to provide interconnection of the transition flange 38 with the connector 
ring 20 (FIG. 1) located on the in-line bipolar connector assembly. 
FIG. 3 is a sectional view through the press-fit sleeve 46. The sleeve is 
provided with an internal cylindrical lumen 50, and is provided with 
chamfers 52 on its proximal and distal ends. An external, circumferential 
groove 48 is provided which it engages with the assembly fixture employed 
to slide the press-fit sleeve 46 relative to the transition flange 38. 
FIG. 4 is a sectional view through transition flange 3. Transition flange 
38 is provided with an internal longitudinal lumen 62, allowing for 
passage of a coiled conductor therethrough. Flange 38 is provided with 
threading 56 on its distal portion and a chamfer 54, facilitating 
insertion of the flange 38 into press-fit sleeve 46. Flange 38 is provided 
with a reduced diameter proximal portion 60 over which the coiled 
conductor 44 (FIG. 2) is placed. The distal end of the coiled conductor 44 
is welded against circumferential shoulder 64. Transition flange 38 is 
also provided with an external circumferential groove 58 which, like 
groove 48 (FIG. 3) is employed to engage the transition flange 38 with the 
assembly fixture employed to slide press-fit sleeve 46 over the distal 
portion of transition flange 38.