The effect of phasic duration on the excitation threshold of biphasic waveforms: a computer model study

Biphasic defibrillation waveforms have been shown to be superior to monophasic defibrillation waveforms in many situations. In a previous work it was shown that a 10-15 ms time window (biphasic preferential window) can be identified in the early diastolic phase of an action potential in which the biphasic threshold is much lower than the corresponding monophasic threshold. The current paper examines effects of phasic duration on the excitation threshold of a biphasic waveform, using a single cell Luo-Rudy phase II membrane model. These results demonstrate that the first pulse and the second pulse may play a very different role in exciting a cell depending on the coupling interval at which an electric defibrillation field is applied and suggest mechanisms for the enhanced defibrillation efficacy of biphasic waveforms.