Current Concepts for Selecting the Location, Size and Shape of Defibrillation Electrodes

Defibrillation would be improved if the shock strength could be decreased. Decreasing shock strength would lessen the chance that the shock itself could damage the heart. With implantable defibrillators, some patients cannot be defibrillated even with the defibrillator at its highest setting; if the shock strength required for defibrillation were sufficiently lowered to bring the required shock voltage into the range of the device, these patients could be defibrillated. Decreasing shock strength requirements would increase the life of the batteries or would allow tbe use of smaller implanted devices. Since the time to charge tbe capacitors would be reduced, it would also shorten the interval until tbe shock was delivered and, hence, decrease the time that tbe patient was without blood flow during fibrillation. Tbe primary variables tbat can be altered to attempt to lower tbe shock strength required for defibrillation include those dealing with the shock waveform, including duration, polarity, and wavesbape, and tbose involving tbe sbock electrodes, including materials of construction, size, shape, and location. This article is concerned witb the last three of tbese variables. It discusses the basic principles, as they are understood today,