Effect of acute global ischemia on cardiac vulnerability to electrical shocks

The goal of this study is to investigate the effect of acute global ischemia on cardiac vulnerability to electrical shocks. Bidomain simulations were performed using a 4 mm thick slice of canine myocardium that incorporates realistic fiber architecture, the blood in the ventricular cavities, and a perfusing bath. Truncated exponential monophasic shocks of 8 ms duration were applied over a range of coupling intervals under normal and ischemic conditions. The three major components of acute ischemia (hyperkalemia, acidosis and hypoxia) were assumed to be present homogeneously in the tissue in a degree that leads to depolarization of resting potential from -85 mV to -66 mV, action potential duration (APD) shortening from 138 to 67 ms, and a 32% decrease of action potential amplitude. Our results show decreased vulnerability to electric shocks during acute global ischemia due to conduction failure caused by: 1) low excitability and reduction of the safety factor for propagation; 2) the simultaneous occurrence of APD shortening and post-repolarization refractoriness.