Difibrillation lead system and method of use

A method of cardioverting the atrium of a human heart, comprising insertion of first and second elongated electrodes tranvenously into the heart and associated vessels. One electrode is preferably located in the coronary sinus and great vein of the heart. The other electrode is preferably located in the vicinity of the atrium of the heart, spaced from the electrode located in the coronary sinus. In response to detection of fibrillation or in response to manual triggering, a defibrillation pulse is applied between the first and second electrodes to effect atrial cardioversion.

BACKGROUND OF THE INVENTION 
The present invention relates to medical electrical leads generally, and 
more particularly to implantable defibrillation electrodes and leads. 
Early concepts of implantable defibrillators, such as disclosed in Reissue 
Pat. No. 27,652 by Mirowski, et al, envision an electrode system employing 
a ventricular endocardial electrode and a plate electrode mounted to the 
heart directly, subcutaneously, or to the skin. However, it has long been 
recognized that a totally transvenous system would be desirable in order 
to simply the use of implantable defibrillators. One such system is 
suggested in Mirowski, et al U.S. Pat. No. 3,942,536, which discloses a 
transvenous lead having electrodes intended for location in the right 
ventricular apex and in the superior vena cava. This electrode system is 
disclosed as useful for either ventricular or atrial defibrillation. Such 
systems were eventually tested in human beings, with some success. 
However, currently available implantable defibrillators typically employ 
epicardial patch electrodes, alone, or in conjunction with transvenous 
electrodes. 
While systems employing epicardial patch electrodes are workable, a 
thoracotomy is required in order to apply the epicardial electrodes. It is 
generally believed that it would be desirable to produce an implantable 
defibrillation system which entirely avoids the necessity of a 
thoracotomy, and there has been substantial work directed towards 
development of such systems, as disclosed in Kallok U.S. Pat. No. 
4,727,877, Tacker, et al U.S. Pat. No. 4,708,145, and as disclosed in U.S. 
application Ser. No. 07/284,957 filed Dec. 15, 1988 by Mehra, for an 
"Endocardial Defibrillation Electrode System". Other endocardial 
defibrillation electrodes are disclosed in Gold et al U.S. Pat. No. 
4,481,953, Kinney, et al U.S. Pat. No. 4,161,952, Kiekhafer et al U.S. 
Pat. No. 4,934,049 and in U.S. Pat. application Ser. No. 07/479,928, filed 
Feb. 14, 1990 by Holleman, et al, for an "Implantable Electrode and Method 
for Fabrication". The Kinney, Gold and Kiekhafer patents and the Holleman, 
et al application all disclose endocardial defibrillation leads employing 
defibrillation electrodes fabricated from elongated coils of biocompatible 
metal, mounted exposed to the exterior of the defibrillation lead, for 
location in the right ventricle and other locations within the heart. The 
above-cited Smits patent and the Mehra application both disclose a variety 
of endocardial defibrillation electrodes intended for use in the atrium, 
ventricle and coronary sinus, all of which employ electrodes taking the 
form of elongated coils of conductive biocompatible metals. 
Concurrent with the development of lead systems adapted to treat 
ventricular fibrillation, there has also been some work directed to the 
development of lead systems to treat atrial fibrillation. Synchronized 
cardioversion using two electrodes located on a lead located in the right 
atrium is disclosed in Charms U.S. Pat. No. 3,738,370. A later system is 
disclosed in Mirowski et al U.S. Pat. No. 3,952,750, employing one 
electrode in the atrium and presumably a second electrode at an 
unspecified location. Neither of these references discloses a specific 
embodiment for the electrodes located in the atrium. 
An electrode lead system specifically designed for atrial defibrillation is 
disclosed in the article "Elective Countershock in Atrial Fibrillation 
With an Intracardiac Electrode--A Preliminary Report, by Jain, et al, 
published in the Journal of the Association of Physicians of India, Vol. 
18, pp 821-824, 1970. This lead was provided with a 10 mm silver 
electrode for location in the right atrium and was tested in conjunction 
with either a second electrode located in the right atrium or a second, 
cutaneous electrode located on the left side of the chest wall. A second 
electrode system specifically designed for use in atrial cardioversion is 
disclosed in the article "Safety and feasibility of transvenous 
cardioversion in atrial tachycardia", by Blanc et al, published in Cardiac 
Pacing, edited by Gomez, Futura Pub. Co., 1985, pp 1526-1529. This 
electrode system employed a single lead with electrodes located in the 
atrium and pulmonary artery. 
SUMMARY OF THE INVENTION 
The present invention is directed toward the provision of an entirely 
endocardial defibrillation lead system particularly optimized for use in 
defibrillation or cardioversion of the atrium. However, the lead system 
may also be used in conjunction with other endocardial electrodes adapted 
to effect ventricular defibrillation. The system disclosed includes 
coronary sinus and right atrial electrodes, and may be embodied with the 
electrodes located on the same or different lead bodies. 
Also disclosed are embodiments in which a ventricular electrode is provided 
so that defibrillation or cardioversion pulses may be delivered between 
the right ventricle and the coronary sinus electrode. In such embodiments, 
the atrial electrode may be located on the same lead as the coronary sinus 
or right ventricular electrode, or may be located on a separate lead.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
FIG. 1 is a cutaway view of the human heart in which a lead system 
embodying the present invention has been implanted. The lead system 
includes two leads, one having its electrode located in the right atrium, 
the other having its electrode located in the coronary sinus. The right 
atrial lead 101 employs an elongated insulative lead body 102, to which a 
coiled defibrillation electrode 106 has been mounted. The distal end of 
the lead includes an electrode head 111, carrying a helical electrode 110 
and a ring electrode 108. The electrodes 106, 108 and 110 are coupled to 
an implantable defibrillator/cardioverter 100 by means of conductors 116, 
118 and 120. The coronary sinus lead 103 also has an elongated insulative 
lead body 104 which carries a coiled defibrillation electrode at its 
distal end, located as generally indicated in broken outline at 112. 
Electrode 112 is located within the coronary sinus and the great cardiac 
vein. Preferably the proximal end of the electrode 112 is spaced about 3 
to 8 cm from the opening of the coronary sinus into the right atrium. The 
curved configuration of lead 101 assists in providing an adequate surface 
area electrode within the atrium and the fixation helix assists in keeping 
the electrode 106 spaced from the opening of the coronary sinus. Depending 
on the size and configuration of the patient's heart, it is anticipated 
that the electrode 106 may extend into the superior vena cava or may be 
located predominantly in the superior vena cava. Maintaining an 
appropriate spacing between the electrodes 112 and 106 is important to 
avoid areas of excessive current density in the regions of their closest 
proximity. 
The electrode 112 is coupled to an implantable defibrillator cardioverter 
100 by means of conductor 122. Electrodes 108 and 110 are used by 
defibrillator cardiovertor 100 to sense the electrical activity of the 
atrium and to diagnose the presence of atrial tachycardias or atrial 
fibrillations requiring cardioversion or defibrillation, respectively. In 
response to the detection of tachycardia or fibrillation, 
defibrillator/cardioverter 100 generates a high voltage pulse between 
electrodes 106 and 112. 
Lead body 102 contains 3 concentric coiled conductors 116, 118, 120, 
illustrated schematically. These three conductors are separated from one 
another by tubular insulative sheaths. This tripolar arrangement is 
illustrated in more detail in Kallok, et al U.S. Pat. No. 4,355,646, 
incorporated herein by reference in its entirety. As set forth in the 
cited Kallok, et al patent, the insulative sheaths employed in the present 
lead may be made of an implantable polyurethane. However, in some 
embodiments, the sheaths may be made of silicone rubber or other 
implantable, flexible plastic. The conductor coils may be made of Drawn 
Brazed Strand wire (DBS), previously used in cardiac pacing leads or may 
be another implantable metal such as MP35N alloy, also commonly used in 
pacing leads. 
The outermost of the three conductor coils within lead body 102 is coupled 
to the proximal end of electrode coil 106 and the middle coil within 
sheath 102 is coupled to ring electrode 108. The innermost coil within 
lead body 102 is mounted rotatably within an insulative sheath separating 
the innermost coil from the middle coil, and is mechanically and 
electrically coupled to helical electrode 110, which is retractably 
mounted within electrode head 111. Rotation of the innermost conductor 
coil causes rotation of electrode 110 and advancement of electrode 110 out 
the distal end of electrode head 111. Electrode 110 may be screwed into 
the tissue of the right atrial appendage of the heart, and is used to 
anchor the lead. The electrode head 111, electrode 110, and the inner most 
conductor coil employed to rotate the helical electrode 110 are described 
in more detail in Bisping U.S. Pat. No. 4,106,512, issued Aug. 15, 1978, 
incorporated herein by reference in its entirety. 
Lead body 104 contains a single coiled conductor, coupled to the proximal 
end of an electrode coil illustrated in broken outline at 112. This 
conductor coil may optionally extend within sheath to the proximal end of 
the lead, and may also be coupled to the distal end of the electrode 112. 
At the distal end of the lead is an insulative plastic tip, not visible in 
this view. 
Electrodes 106 and 112 may be mounted around insulative lead bodies 102 and 
104 and bonded to them by means of a backfill of insulative plastic, as 
described in Kiekhafer, et al U.S. Pat. No. 4,934,049, on Jun. 19, 1990, 
and incorporated herein by reference in its entirety. As an alternative, 
the insulative lead bodies 102 and 104 may be fabricated of a polyurethane 
or other heat flowable material, expanded against the interior of the 
electrode coils under pressure and heat to allow the material of the 
sheath to flow between the electrode coils, as illustrated in U.S. Pat. 
application Ser. No. 07/479,928, filed on Feb. 14, 1990 for an 
"Implantable Electrode and Method for Fabrication" by Holleman, et al, 
also incorporated herein by reference in its entirety. Alternatively, the 
electrode coils may be fabricated using the techniques illustrated in the 
above cited Kinney or Gold patents. Electrodes 30 and 32 are preferably 
made of platinum. However, as discussed in the references cited above, 
other implantable metals have been disclosed for use in such electrodes. 
The curved configuration of electrode 106 as illustrated is maintained by 
any of a number of known mechanisms. It may be maintained by means of 
molding lead body 102 in the form of a curved tube, or otherwise imparting 
a predetermined curve thereto. For example, the techniques illustrated in 
Berkovitz U.S. Pat. No. 3,729,008, also incorporated herein by reference 
in its entirety may ba adapted. Alternatively, the electrode coil 106 may 
be preformed to exhibit a curved configuration. An additional preformed 
curved coil devoted particularly to maintaining the curved configuration 
of the lead may also be used, as disclosed in Lindemans U.S. Pat. No. 
4,402,330, issued on Sep. 6, 1983, also incorporated herein by reference 
in its entirety. 
A specific example of a defibrillation pulse generator which may be used in 
conjunction with the present lead is disclosed in Mehra et al U.S. Pat. 
No. 4,953,551, issued on Sep. 4, 1990, incorporated herein by reference in 
its entirety. An addition example of an appropriate pulse generator is 
disclosed in U.S. Pat. application Ser. No. 07/612,758 for an "Apparatus 
for Delivering Single & Multiple Cardioversion Pulses", filed Nov. 14, 
1990, by Keimel and also incorporated herein by reference in its entirety. 
While it is envisioned that the present application may most beneficially 
be practiced in conjunction with an implantable cardioverter/defibrillator 
which has the capability of sensing the electrical activity of the heart 
to detect the presence of atrial tachycardia or fibrillation, the 
invention may also be usefully practiced in conjunction with a device as 
disclosed in Mirowski et al U.S. Pat. No. 3,952,750, issued on Apr. 27, 
1976, incorporated herein by reference in its entirety. In devices as 
illustrated in the Mirowski et al. patent, the detection of atrial 
fibrillation is not accomplished by the implanted device. Instead, the 
presence of atrial fibrillation is detected either by a physician or the 
patient, and a signal is generated external to the device, triggering 
delivery of a synchronized atrial defibrillation pulse. This approach is 
made possible by the fact that atrial fibrillation, unlike ventricular 
fibrillation, does not result in the cessation of the heart's pumping 
action. 
FIG. 2 is a cutaway view of the human heart illustrating an alternative 
embodiment of the present invention employing an atrial lead having a 
generally straight defibrillation electrode 206 and a coronary sinus 
defibrillation lead 203 provided with sensing electrodes 208 and 210. The 
electrode lead 203 may correspond to the coronary sinus defibrillation 
lead illustrated in FIG. 2 of allowed U.S. Pat. application Ser. No. 
07/284,957, filed Dec. 15, 1988 by Mehra, for an "Endocardial 
Defibrillation Electrode System" incorporated herein by reference. Like 
the atrial lead 101 discussed in conjunction with FIG. 1, lead 203 has a 
tripolar configuration, employing three coaxial conductors 116, 118 and 
120, each coupled to one of electrodes 208, 210 and electrode 212, 
indicated in broken out line within the coronary sinus. Electrodes 208 and 
210 function to sense the electrical activity of the atrium of 
defibrillation detection and/or cardiac pacing. 
Electrode lead 201 corresponds to the lead illustrated in FIG. 2 of the 
above-cited allowed application by Mehra et al., however it omits sensing 
electrodes corresponding to electrodes 208 and 210, and includes only a 
single conductor 122, mounted within insulative lead body 202, coupled to 
electrodes 206. A pliant insulative tip 124 is visible. A corresponding 
pliant, insulative tip is located on the distal end of lead 203, not 
visible in this view and on the distal end of lead 101, FIG. 1. As in the 
case of electrode 106, FIG. 1, electrode 206 may extend proximally into 
the superior vena cava or may be located predominantly in the superior 
vena cava. 
The construction of electrodes 206 and 212 corresponds to the construction 
of electrodes 106 and 112, as discussed above in conjunction with FIG. 1. 
As in the case of the system illustrated in FIG. 1, 
defibrillator/cardioverter 200 delivers defibrillation pulses between 
electrodes 206 and 212, either in response to detection of atrial 
tachycardia or fibrillation via electrodes 208 and 21? or in response to 
an external command signal. 
FIG. 3 is a cutaway view of the heart illustrating yet another embodiment 
of an electrode system embodying the present invention. In this 
embodiment, a first electrode lead 301 is provided with two defibrillation 
electrodes 306 and 312, both located around its insulative lead body 302. 
Lead 301 is a bipolar lead, employing two conductors 320 and 322 located 
coaxially within lead body 302. Electrodes 306 and 312 may correspond to 
electrodes 106 and 112, illustrated in FIG. 1. Electrode 306 is provided 
with a preformed, J-shaped configuration corresponding to that of 
electrode 106, illustrated in FIG. 1 which assists both in maintaining the 
lead in its location within the heart and allows for a substantial surface 
area of the electrode 306 to be located in the right atrium, while 
remaining spaced from the ostium of the coronary sinus. Electrode 312 is 
located within the coronary sinus and great vein also, spaced from the 
ostium of the coronary sinus. An interelectrode spacing of at least about 
5.sub.-- cm is believed desirable. This assists in providing good 
intraelectrode separation between electrode 306 and 312. As a practical 
matter, this interelectrode spacing may result in electrode 306 being 
predominantly located in the superior vena cava in some patients. 
A second lead 303 is provided which is also triaxial lead in which three 
conductors, 324, 326 and 328 are located coaxially within insulative lead 
body 304. Each of these conductors is coupled to one of defibrillation 
electrode 330, ring electrode 332 or helical electrode 334. With the 
exception of the omission of the J-shaped bend, lead 303 corresponds 
exactly to lead 101, illustrated in FIG. 1. 
As illustrated, this electrode system is provided with electrodes 332 and 
334 allowing for sensing of ventricular electrical activity, but is not 
provided with a separate set of electrodes for sensing electrical activity 
in the atrium. As such, as illustrated, it is anticipated that the 
cardioverter/defibrillator 300 will automatically delivery high voltage 
pulses between electrode 330 and electrode 312 in response to detection of 
ventricular tachycardia or fibrillation. However, delivery of atrial 
cardioversion or defibrillation pulses between electrode 306 and electrode 
312 would be triggered externally by the patient or a physician in 
response to detection of symptoms indicative of atrial fibrillation or 
atrial tachycardia. In such an embodiment, an internal override disabling 
the ability to trigger atrial cardioversion/defibrillation shocks may be 
desirable in response to internal detection of electrical activity which 
is reliably identified as ventricular tachycardia or ventricular 
fibrillation rather than rapid ventricular rates due to atrial 
fibrillation or atrial tachycardia. 
FIG. 4 is a cutaway view of the heart illustrating yet another embodiment 
of the present invention. This embodiment includes a lead 401, which has 
defibrillation electrodes 406 and 430 mounted to its insulative lead body 
402, and located in the right atrium and right ventricular, respectively. 
The lead also includes a helical electrode 434, corresponding to the 
helical electrode 110, illustrated in conjunction with lead 101, FIG. 1. 
As in the case of lead 101, illustrated in FIG. 1, lead 401 is a coaxial, 
tripolar lead having coaxial conductors 420, 424 and 426 coupled to 
electrodes 406, 430 and 434. Lead 403 corresponds exactly to lead 203, 
illustrated in FIG. 2 and is provided with ring electrodes 408 and 410 and 
with a defibrillation electrode, each coupled to one of three conductors 
416, 418 and 420. It is anticipated that in some cases, this electrode 
configuration will be practiced by employing a lead as disclosed in the 
above cited Mirowski patent, employing right ventricular and SVC 
electrodes in conjunction with a coronary sinus lead as disclosed in the 
above cited Mehra application. 
In this embodiment, the defibrillator/cardioverter 400 is configured such 
that it may sense electrical activity in the atrium via electrodes 408 and 
410 and may sense electrical activity in the ventricular via electrode 434 
and a remote, different electrode, or between electrode 434 and electrode 
430. In response to detection of ventricular tachycardia, 
cardioverter/defibrillator 400 generates a high voltage pulse between 
electrodes 430 and 412. In response to detection of atrial tachycardia or 
fibrillation, defibrillator/cardioverter 400 delivers a high voltage 
between electrodes 406 and 412. As such, the lead system illustrated is 
particularly beneficial if atrial and ventricular cardioversion and 
defibrillation functions are desired to be combined within the same 
device. Selection between electrodes 406 and 430 may be accomplished using 
a defibrillation/cardioversion pulse generator as disclosed in the 
above-cited Keimel et al. application, or using other defibrillation pulse 
generators capable of being programmed to deliver pulses between multiple 
pairs of electrodes, as disclosed in the article "A Multielectrode--Time 
Sequential Laboratory Defibrillator for the Study of Implanted Electrode 
Systems", by Schuder et al, published in Transactions of the American 
Society of Artificial Organs, Vol. XVIII, pp 514-519, 1972, incorporated 
herein by reference in its entirety. 
The inventive atrial cardioversion and defibrillation lead system is shown 
in conjunction with an endocardial ventricular electrode, if ventricular 
defibrillation capabilities are desired. However, the endocardial 
ventricular electrode may be replaced by or augmented with a subcutaneous 
patch electrode, which may correspond to any of the previously known 
subcutaneous patch electrodes. Alternatively, if the atrial defibrillation 
system is to be added to a previously existing ventricular defibrillation 
lead system, the endocardial ventricular electrode may be substituted with 
a left ventricular epicardial electrode. 
Appropriate epicardial electrodes are illustrated in Holleman et al U.S. 
Pat. No. 4,817,634, issued Apr. 4, 1989, and incorporated herein by 
reference in its entirety. Appropriate subcutaneous electrodes may take 
the form of the electrodes illustrated in U.S. Pat. application Ser. No. 
07/376,730 by Lindemans et al, filed Jul. 7, 1989 for a "patch electrode", 
also incorporated herein by reference in its entirety. The location of the 
subcutaneous electrode will vary from patient to patient, depending upon 
the particular geometry of the patient's heart, the other electrodes 
present and other considerations of bodily structure. 
As discussed above, the electrode system and its method of application may 
be beneficially practiced in a wide variety of contexts, including 
automatic and nonautomatic cardioverters and defibrillators, which may or 
may not include additional electrodes dedicated toward provision of 
ventricular defibrillation pulses. Similarly, the electrodes employed to 
perform atrial defibrillation may be located on leads having a wide 
variety of configurations. While some of the configurations illustrated 
are specifically claimed below, these particular configurations should not 
be considered limiting with regard to claims to the general method set 
forth above or claims directed generally to lead systems appropriate for 
carrying out the claimed method. As such, the above illustrated 
embodiments should be considered exemplary, rather than limiting with 
regard to the claims presented below.