Improved defibrillation thresholds with large contoured epicardial electrodes and biphasic waveforms.

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Abstract
A reduction in the shock strength required for defibrillation would allow use of a smaller automatic implantable cardioverter-defibrillator and would reduce the possibility of myocardial damage by the shock. Most internal defibrillation electrodes require 5 to 25 J for successful defibrillation in human beings and in dogs. In an attempt to lower the shock strength needed for defibrillation, we designed two large titanium defibrillation patch electrodes that were contoured to fit over the right and left ventricles of the dog heart, covering areas of approximately 33 and 39 cm2, respectively. In six anesthetized open-chest dogs, the electrodes were secured directly to the epicardium and ventricular fibrillation was induced by 60 Hz alternating current. Truncated exponential monophasic and biphasic shocks were given 10 sec later and defibrillation thresholds (DFTs) were determined. The DFT was 159 +/- 48 V, 3.2 +/- 1.9 J (mean +/- SD) for 10 msec monophasic shocks and 106 +/- 22 V, 1.3 +/- 0.4 J, for biphasi...