Mechanisms by which AC leakage currents cause complete hemodynamic collapse without inducing fibrillation

AC-Induced Non-VF Collapse. Introduction: The first study of weak alternati ng current (AC) stimulation in closed chest humans showed that complete hem odynamic collapse can occur below the threshold for inducing ventricular fi brillation (VF), a heretofore unknown danger to patients. This article, and the accompanying simulation article, explore the mechanisms responsible fo r the collapse. Methods and Results: A quadripolar pacing catheter was placed in the right ventricle (RV) of six dogs. The tip of the catheter (17 mm(2)) carried 5 se conds of AC stimulation ranging from 10 to 160 Hz and 10 to 1,000 muA. The lead H body surface ECG, femoral artery pressure, and a bipole from the pro ximal pair of electrodes on the RV catheter were recorded 2 seconds before, during, and 2 seconds after stimulation. Based on the blood pressure, ever y episode was categorized as VF, COLLAPSE without VF, extrasystolic without COLLAPSE (EFFECT), or having caused no effect (NSR). The electrical activa tion interval (interspike interval [ISI]) from the RV bipole was compared w ith the mechanical activation interval, determined from M-mode ultrasound. COLLAPSE is associated with a short ISI (NSR = 408 +/- 110 msec; EFFECT = 3 05 +/- 113 msec; COLLAPSE = 179 +/- 25 msec; P < 0.001) with a high degree of regularity (P < 0.001): coefficient of variation of ISI for COLLAPSE (0. 038 +/-0.069) versus VF (0.389 +/-0.222), EFFECT (0.420 +/-0.241), and NSR (0.016 +/-0.048). Electrical activation and mechanical activation rates occ urred at integer multiples of the AC stimulation period. Conclusion: COLLAPSE (86 +/- 37 muA; minimum 50 muA in two animals) occurs below the VF threshold (108 +/- 28 muA) by causing rapid, regular excitatio n.