Electrophysiological disturbances associated with acute myocardial infarction

By the time most patients reach hospital with acute myocardial infarction the risk of developing ventricular fibrillation (VF) is receding and Q wave evolution is complete. While these changes are the culmination of a single irreversible ischaemic insult, this may follow several reversible episodes of ischaemia associated with marked ECG changes during the preceding hours or days and further ischaemic episodes may follow the development of Q waves. Cellular electrophysiological changes associated with experimental myocardial ischaemia in an isolated guinea pig preparation were a reduction in refractory period and action potential amplitude, Vmax and duration while conduction time and QRS width were prolonged. Spontaneous recovery in action potential amplitude and Vmax was observed after 12 min of ischaemia and depended on the presence of residual coronary flow. Electrophysiological recovery commenced rapidly on reperfusion but with further shortening of action potential duration. Reperfusion VF was most likely to occur when the associated ischaemic insult was 20-30 min in duration. Myocardial catecholamine depletion significantly reduced these arrhythmias and this antiarrhythmic action was associated with marked attenuation of the electrophysiological effects of ischaemia and reperfusion.