60 Hz leakage currents cause complete hemodynamic collapse below VF threshold

Two figures are presented. The first figure summarizes the data showing the threshold for simulation (bold line), the minimum for ventricular fibrillation (VF) (dotted line) and the average value for collapse. With the exception of one point (80 Hz), there is always a point below the strength causing VF where AC stimulation causes complete systemic pressure collapse, but not VF. The mechanism is still under investigation, but appears to be the induction of a hemodynamically compromised tachycardia. The second figure shows that the data for collapse is very well described by the Hill equations. This suggests that the same cellular mechanisms that underlie AC stimulation of nervous tissue underpin AC stimulation of cardiac tissue. For increasing frequencies, the current threshold increases because insufficient charge is delivered in each pulse and because the stimulus can reverse a developing action potential. At very low frequencies, the rate of change is low enough that the current leakage across the membrane counteracts the buildup of a depolarizing transmembrane voltage