Experimental results pertinent to the modelling of defibrillation

Recent experimental results pertinent to the modeling of defibrillation are presented. The extracellular potential gradient created by a large electric stimulus predicts whether or not several different types of electrophysiologic response will occur for a given stimulus waveform. Stimulation of fully recovered myocardium occurs for a truncated exponential monophase waveform when the potential gradient is greater than 0.64 V/cm along myofibers or 1.84 V/cm across fibers. A potential gradient of approximately 6 V/cm is needed throughout for all or almost all of the ventricular myocardium to defibrillate. More than approximately 60 V/cm causes a temporary conduction block. Thus, defibrillation electrode configurations should create cardiac fields with the highest gradient no more than ten times the lowest gradient. Values for stimulation, defibrillation, and conduction block are probably different for other waveforms