"Within the first minutes after experimental coronary ligation, there is a propensity to ventricular arrhythmias that abates after 30 minutes and reappears after several hours. The initial 30 minutes of arrhythmias is divided into two periods, the first of which lasts for about 10 minutes and is presumably directly related to the initial ischemic injury. The second period (20 to 30 minutes) may be related either to reperfusion of ischemic areas or to the evolution of different injury patterns in the epicardial and endocardial muscle. Multiple mechanisms of reperfusion arrhythmias have been observed experimentally, including slow conduction and reentry and afterdepolarizations and triggered activity."
"At the level of the myocyte, the immediate consequences of ischemia, which include alterations of cell membrane physiology, with efflux of K+, influx of Ca2+, acidosis, reduction of transmembrane resting potentials, and enhanced automaticity in some tissues, are followed by a separate series of changes during reperfusion. Those of particular interest are the possible continued influx of Ca2+, which may produce electrical instability; responses to alpha or beta adrenoceptor stimulation, or both; and afterdepolarizations as triggering responses for Ca2+-dependent arrhythmias. Other possible mechanisms studied experimentally include formation of superoxide radicals in reperfusion arrhythmias and differential responses of endocardial and epicardial muscle activation times and refractory periods during ischemia or reperfusion. The adenosine triphosphate–dependent K+ current (IK.ATP), which is inactive during normal conditions, is activated during ischemia. Its activation results in a strong efflux of K+ ions from myocytes, markedly shortening the time course of repolarization and leading to slow conduction and ultimately to inexcitability. The fact that this response is more marked in epicardium than in endocardium leads to a prominent dispersion of repolarization across the myocardium during transmural ischemia. At an intercellular level, ischemia alters the distribution of connexin43, the primary gap junction protein between myocytes. This alteration results in uncoupling of myocytes, a factor that is arrhythmogenic because of altered patterns of excitation and regional changes in conduction velocity."(Braunwald's Heart Disease 8th Edition)