Intracardiac defibrillation requires the lowest possible defibrillation threshold in order to extend battery life and to increase a safety margin. An optimal choice of size, shape and position of the electrodes with respect to the heart can contribute to this goal. In 11 dogs 349 episodes of ventricular fibrillation were induced and four different defibrillation electrodes used. After ventricular fibrillation was detected a shock with programmable width between 1.5 and 2.4 ms was delivered after 20 seconds. Successful defibrillation was considered if sinus rhythm and adequate aortic pressure were detected. Percentage success rate (%SR) was calculated as: %SR=100/spl times/number of effective shocks/total number of shocks. The threshold/duration curve showed a parabolic behavior with a minimum at 10 ms. Sigmoid curves proved to give a best fit %SR. Ti electrodes showed a 90% SR at 16.5 J, circular patches at 13.5 J, cross patches at 9 J and Cu spoons at 8 J. These results indicate the possibility to optimize electrode configuration and threshold for a individual patient with a limited number of test shocks.
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