Cellular excitation with high-frequency chopped defibrillator waveforms

Waveform shape and stimulus intensity are both critical in determining efficacy of defibrillating waveforms. Defibrillator waveforms for which the electrode current is interrupted or chopped at high frequency may alter current flow patterns in the heart and thereby lower defibrillation threshold. However, cellular effects of high-frequency chopped waveforms are unknown. Defibrillation may occur due to production of prolonged refractory period responses which prolong the fibrillation action potential through mechanisms similar to excitation. To test the hypothesis that cells can be excited by current which is chopped into many high frequency pulses, the authors examined effects of chop frequencies ranging from 0.05 to 25 kHz on cellular excitation threshold. The results show that excitation threshold depends on chop frequency in a theoretically predictable manner which suggests that the cell membrane integrates individual pulses at frequencies greater than 5 kHz