Mechanisms of ventricular fibrillation induction by 60-Hz alternating current in isolated swine right ventricle

Background-The mechanisms by which 60-Hz alternating current (AC) can induc e ventricular fibrillation (VF) are unknown. Methods and Results-We studied 7 isolated perfused swine right ventricles i n vitro. The action potential duration restitution curve was determined. Op tical mapping techniques were used to determine the patterns of activation on the epicardium during 5-second 60-Hz AC stimulation (10 to 999 mu A). AC captured the right ventricles at 100 +/- 65 mu A, which is significantly l ower than the direct current pacing threshold (0.77 +/- 0.45 mA, P<0.05). A C induced ventricular tachycardia or VF at 477 +/- 266 mu A, when the stimu lated responses to AC had (1) short activation CLs (128 +/- 14 ms) (2) shor t diastolic intervals (16 +/- 9 ms), and (3) short diastolic intervals asso ciated with a steep action potential duration restitution curve. Optical ma pping studies showed that during rapid ventricular stimulation by AC, a wav e front might encounter the refractory tail of an earlier wave front, resul ting in the formation of a wave break and VF. Computer simulations reproduc ed these results. Conclusions-AC at strengths less than the regular pacing threshold can capt ure the ventricle at fast rates. Accidental AC leak to the ventricles could precipitate VF and sudden death if AC results in a fast ventricular rate c oupled with a steep restitution curve and a nonuniform recovery of excitabi lity of the myocardium.