Mechanisms of electrical defibrillation: impact of new experimental defibrillator waveforms.
Six possible explanations for why some biphasic waveforms have lower defibrillation thresholds than monophasic waveforms of the same duration are as follows: (1) the impedance for the second phase of the biphasic shock is very low because electrode polarization develops during the first phase; (2) the large change in voltage between the first and second phases of a biphasic waveform is responsible for the increased defibrillation efficacy; (3) biphasic waveforms cause less severe detrimental effects in regions of high potential gradient; (4) the first phase of the biphasic waveform restores activity of the sodium channels, which makes defibrillation easier for the second phase; (5) the potential gradient required for defibrillation is less for biphasic waveforms than for monophasic waveforms; and (6) biphasic waveforms are better able to stimulate the myocardium to induce new action potentials or to cause refractory period prolongation. Evidence shows that, while a few of these proposed mechanisms are incorrect, several of the others may together contribute to the general superiority of biphasic waveforms.
Blanchard
S M
SM
Department of Biomedical Engineering, Duke University, Durham, NC.
Ideker
R E
RE
D000200:Action Potentials / Q000502:physiology; D000818:Animals; D001281:Atrial Fibrillation / Q000628:therapy; D004554:Electric Countershock / Q000379:methods*; D017097:Electric Impedance; D006801:Humans; D014693:Ventricular Fibrillation / Q000628:therapy