Method for high energy defibrillation of ventricular fibrillation in humans without a thoracotomy

Defibrillation of ventricular fibrillation and cardioversion of ventricular tachycardia is accomplished by single, bidirectional high energy shocks from two anodes to a common cathode. All the electrical apparatus is implanted without a thoracotomy.

This invention relates to a method for defibrillating ventricular 
fibrillation and cardioversion of ventricular tachycardia in humans by 
means of single bidirectional high energy electrical shocks from implanted 
shock generator apparatus. 
Ventricular fibrillation is an irregular uncoordinated action of the fibers 
of the heart muscle, which results in a failure of the heart to pump 
blood. Unless corrective action is taken promptly, death results in a few 
minutes. 
Ventricular tachycardia also involves some irregularity of the rythmic 
action of the heart muscle but is primarily characterized by an abnormally 
fast and altered contraction pattern. Ventricular tachycardia is subject 
to being accelerated into ventricular fibrillation by a number of known 
factors or stimuli, including inadvertently by means of electrical 
impulses from a cardioverter apparatus. 
These disorders (ventricular fibrillation and ventricular tachycardia) 
result in cessation of adequate pump function of the heart and sudden 
cardiac death. This is the leading cause of death in the United States; it 
is believed that more than 300,000 individuals in the United States 
experience such events annually. 
Implantable pacemakers have been employed for several years. They are 
characterized by employing electrical impulses of relatively low energy. 
They are useful for a few selected patients having ventricular tachycardia 
with rates below 200 beats per minute, but not for a much larger number of 
patients who chronically or on occasion have faster ventricular 
tachycardia. Pacemakers are ineffective for defibrillating ventricular 
fibrillation, and are known to have inadvertently accelerated ventricular 
tachycardia into ventricular fibrillation on some occasions. 
Cardioverter and/or defibrillator devices have been in development for more 
than a decade. Early prototypes employed a pair of electrodes disposed on 
a catheter inserted into the heart transvenously. One electrode, serving 
as a cathode, was located at the distal end of the catheter and positioned 
in the right ventricle near the apex thereof. A second electrode on the 
catheter was positioned in the right atrium of the heart or at the 
superior vena cava. Cardioversion or defibrillation was accomplished by 
shocks of electrical energy, passing from the anode to the cathode, 
lasting a few to several milliseconds. The foregoing procedure is 
characterized as a uni-directional electrical shock.

U.S. Pat. No. 4,548,203 describes a process of sequential bidirectional 
shocks, in which two separate shocks are released, from two spatially 
separated anodes in a timed sequence. As depicted in FIG. 3a, a cathode 
and a first anode electrode, both catheter-borne, are positioned, 
respectively, in the right ventricle and the superior vena cava, as 
described above. A second anode electrode is positioned on the outside of 
the left ventricle. In operation according to the method described in such 
patent, a first electrical shock is passed between one anode and the 
cathode, and shortly thereafter, a second shock is passed from the second 
anode to the cathode. Thus, the foregoing is referred to as a sequential, 
bidirectional system. In an alternative configuration described in the 
patent, two pairs of electrodes may be employed, as depicted in FIG. 2. 
Each electrode of a pair is positioned opposite the other and in the 
pericardial space between the outer surface of the heart (the epicardium) 
and the sac (the pericardium) enclosing the heart. The four electrodes are 
orthogonal to each other. In this configuration, there is no 
catheter-borne electrode. In operation, a first shock is passed between 
two electrodes forming one pair, and the shortly thereafter, a second 
shock is passed between the electrodes of the second pair. 
The foregoing sequential, bidirectional method of imparting electrical 
shocks to the heart has two distinct disadvantages. One is that a 
thoracotomy (i.e., an opening of the chest wall) is required. This fact is 
apparent from FIGS. 10-12, depicting a part of the surgical procedure for 
positioning pairs of electrodes in the pericardial space, and also from 
the location, on the outer left ventricle, of the second anode 37 of FIG. 
3a. 
Secondly, an inherent requirement of a sequential shock system is the 
necessity of having two capacitors and two power sources as part of the 
shock-generating apparatus. This necessity is a significant disadvantage 
in respect of implantable apparatus, because it inherently increases the 
size and weight of the apparatus relative to that which can be designed 
specifically for a single shock, bidirectional system as described 
hereinafter. 
As of the current time, the method described in U.S. Pat. No. 4,548,203 has 
never been employed as a human implant system for defibrillation of 
ventricular fibrillation or cardioversion of ventricular tachycardia. 
The sequential, bidirectional system with electrodes positioned as in FIG. 
3a of U.S. Pat. No. 4,548,203 is also described by D. L. Jones, et al., in 
"Internal Cardiac Defibrillation In Man: Pronounced Improvement With 
Sequential Pulse Delivery To Two Different Lead Orientations", 
Circulation, vol. 73, No. 3, pages 484-491 (March 1986). Such article 
describes the application of the method to human patients, including the 
fact that the chest wall was opened by means of a mediam sternotomy. There 
is no reference in the article to actually implanting the shock generator 
apparatus and electrodes. 
It is accordingly an object of this invention to provide a method for the 
defibrillation of ventricular fibrillation or the cardioversion of 
ventricular tachycardia by means of single, bidirectional, high energy 
electrical shocks administered to the heart by means of implanted 
electrodes and implanted shock generator apparatus. 
The method is for the high energy defibrillation of ventricular 
fibrillation or ventribular tachycardia in humans. It comprises subjecting 
the heart to a single, bidirectional high energy electrical shock from a 
first anode and a second anode to a cathode. The energy of the shock is at 
least 15 Joules, delivered over a period of time of not less than about 2 
milliseconds to the anodes by an implanted shock generator. The cathode is 
transvenously positioned in the right ventricle. The first anode is 
transvenously positioned near the superior vena cava or in the right 
atrium. The second anode is positioned subcutaneously in the left half 
side of the chest and outside the rib cage. The two anodes are 
electrically connected in parallel to the shock generator. Both anodes and 
the cathode are electrically connected to the shock generator via 
implanted leads. The three electrodes, the leads and the shock generator 
are implanted without a thoracotomy. 
For the defibrillation of ventricular fibrillation or cardioversion of 
ventricular tachycardia, the wave form of the electrical shock may be 
truncated exponential, rectangular, biphasic or sinusoidal. A truncated 
exponential wave form is preferred, having a tilt in the range of from 
about 15 degrees to about 80 degrees. The initial voltage at the start of 
the shock should be not less than about 300 volts, and may be as high as 
600-750 volts. The trailing edge of a truncated wave form should be not 
less than 50 volts. The duration of the shock should be at least about 2 
milliseconds, and may be much longer, such as 30-60 milliseconds, although 
usually a maximum of 15 milliseconds will suffice. The amount of energy 
employed per shock should be at least 15 Joules, and preferably from about 
25 to about 30 Joules, for defibrillation or cardioversion of ventricular 
tachycardia. Additional energy may be employed providing the amount is not 
so great as to damage the tissue of the heart. 
The defibrillation method may also optionally comprise imparting a second 
shock, in the same manner as the first shock, within about two minutes of 
the termination of the latter. The shock generator apparatus may also be 
designed to impart a third or a fourth shock. 
It will be understood by those skilled in defibrillation of ventricle 
fibrillation and cardioversion of ventricular tachycardia that the minimum 
effective, and the maximum permissible, shock energy, voltage and duration 
for defibrillation varies from human to human, depending upon many 
factors, including illustratively the size and condition of an individual 
heart. This lack of uniformity, which is typical of medical science, 
precludes a precise quantitative statement of the ranges of physical 
parameters which will be uniformly applicable to all humans under all 
conditions. 
Apparatus with which to practice the invention has been developed 
previously. The apparatus includes a catheter adapted to be transvenously 
inserted into the heart, and bearing at its distal end an electrode 
adapted to serve as a cathode, and, about 10-15 centimeters towards the 
proximal end, an electrode adapted to serve as a first cathode. The second 
anode is typically a patch electrode positioned subcutaneously outside the 
rib cage in the left half of the upper torso and above the diaphragm (i.e. 
outside the left anterior and posterior of the chest wall). The second 
anode is preferably positioned under any muscle which exists at the 
location selected. It is also preferably located in a horizontal plane 
through the fourth left intercostal (rib) space at the mid-axillary (arm 
pit) line. 
The shock-generating apparatus should be implantable and deliver a single 
shock discharge. Thus such apparatus can be designed with only a single 
discharge capacitor if desired. The shock-generating apparatus is 
connected through implanted leads to the electrodes described herein. The 
first and second anodes are connected in parallel electrically to a 
discharge capacitor of the shock generator apparatus. Optionally, such 
apparatus may also have sensing means for sensing and measuring the action 
of the heart and initiating an electrical shock of pre-programmed duration 
and amount of energy in response to such sensing means. Although currently 
known shock-generator apparatus may be employed, it is anticipated that 
refinements in the design thereof for use in the single shock, 
bidirectional process described herein can result in apparatus of lesser 
size and weight and therefore be more acceptable to patients and surgeons. 
The drawing depicts apparatus that may be employed in practicing the 
process described and claimed herein. The drawing shows the upper portion, 
from the neck to the midsection, of a human torso 10, having a heart 12. A 
catheter 14 is shown transvenously inserted into heart 10. The catheter 
bears at its distal end an electrode adapted to serve as a cathode 16, and 
positioned in the right ventricle of the heart 12. A first anode 18 is 
borne by the catheter 14 at a point about 10-15 centimeters from the 
distal end thereof, and positioned near the superior vena cava or in the 
right atrium of the heart 12. A second anode 20, such as a patch 
electrode, is disposed subcutaneously outside the torso's rib cage. It is 
preferably located along the mid-axillary (arm pit) line in a horizontal 
plane through the fourth left intercostal (rib) space, but for the sake of 
ease of understanding and clarity of depiction in the drawing, said second 
anode 20 is shown displaced somewhat to the right of said mid-axillary 
line. 
First anode 18 and second anode 20 are connected electrically in parallel 
via implanted leads 22 and 24 to the discharge terminal of a capacitor 
(not shown) in an implanted shock generator apparatus 26, illustratively 
of the type referred to in the following paragraph. The sets 28 and 30 of 
dashed lines depict the pathway of electrical energy from, respectively, 
the first anode 18 and the second electrode 20, to the cathode 16. 
The method described herein has been recently employed in a man aged 69 
employing an implanted permanent non-epicardial triple electrode system in 
a patient with recurrent ventricular tachycardia and ventricular 
fibrillation and severe pulmonary disease who could not undergo an 
operation involving open chest surgery. A large patch electrode was placed 
over the rib cage in the mid-axillary line at the level of the left fourth 
intercostal space. A tripolar catheter was placed in the right ventricular 
apex and was used for sensing and shock delivery. An intracardiac 
cardioversion-defibrillation catheter (ICDC), available from Cardiac 
Pacemakers, Inc., of Minneapolis, Minn., was employed. The distal right 
ventricular electrode was the common cathode. The proximal superior vena 
cava/right atrial electrode and the subcutaneous patch were 
cross-connected with a Y-connector as dual anodes. Employing the foregoing 
configuration and apparatus, a single 10 Joule bidirectional shock 
resulted in successful defibrillation of ventricular fibrillation during 
testing with an external shock generator prior to implanting a permanent 
shock generator. The defibrillation threshold was less than 10 Joules. The 
implanted shock generator was an Automatic Implantable 
Cardioverter/Defibrillator, also available from Cardiac Pacemakers, Inc. 
Postoperative electrophysiologic studies demonstrated continued successful 
defibrillation of ventricular fibrillation with the foregoing system.