Ambinder DI, Patil KD, Kadioglu H, et al. - In cardiac arrest, pulseless electrical activity (PEA) is a common initial rhythm. As coronary ischemia causes a substantial number of PEA arrests in the setting of acute coronary occlusion, researchers herein tested their hypothesis that the initial rhythm in patients with acute coronary occlusion is more likely to be PEA than ventricular fibrillation in those with prearrest severe left ventricular dysfunction. Swine without and with preexisting severe left ventricular dysfunction induced by prior infarcts in non–left anterior descending coronary territories were studied for the initial cardiac arrest rhythm induced by acute left anterior descending coronary occlusion. Eighteen of 34 naïve animals showed ventricular fibrillation following balloon occlusion, occurring 23.5±9.0 minutes following occlusion, and PEA occurred in 1 animal. However, PEA developed in all 18 animals with severe prearrest left ventricular dysfunction (ejection fraction 15±5%) 1.7±1.1 minutes after occlusion. In the setting of severe left ventricular dysfunction, acute coronary ischemia produces PEA because of acute pump failure, an occurrence of which is noted almost immediately following coronary occlusion. Overall findings support the notion that acute coronary occlusion should be evaluated in patients with baseline left ventricular dysfunction and suspected coronary disease who develop PEA.