Optimal truncation of defibrillation pulses.
The statement that the optimal pulse for defibrillation has not yet been discovered implies that an ideal pulse exists, but that it is different in shape, duration, and energy as compared to pulses of today. The optimum pulse is that which can defibrillate with lowest energy. Reduction of energy can be reached twofold: by looking for a pulse duration with lowest energy threshold, and by finding the optimal truncation with lowest refibrillating effect. Assuming that there is also a rheobase in defibrillation below which no defibrillating but probably a refibrillating effect exists, the exponential pulse should be truncated if it intersects with the rheobase. Combining the fundamental law of electrostimulation with this boundary condition allows for the mathematical solution of the above problem of optimal energy. Defibrillation can be optimized with respect to pulse duration or tilt and to energy efficiency. The most important parameter in determining other optimized parameters such as output capacitor is the chronaxie. The calculations reveal that the "concept of constant energy" does not accurately describe defibrillation, that today's implantable cardioverter defibrillator devices possess refibrillating tilts, that pulse durations should be programmed to values between 4 and 10 msec, and that smaller output capacitors around 30 microF would minimize the energy requirements. Whether optimized monophasic pulses are inferior or equal to biphasic pulses needs further experimental studies.
Irnich
W
W
Department of Medical Engineering, Justus-Liebig-University, Giessen, Germany.
D017147:Defibrillators, Implantable; D004554:Electric Countershock / Q000592:standards*; D006801:Humans; D008955:Models, Cardiovascular; D011674:Pulse