The electrocardiographic diagnosis of acute myocardial infarction in patients with ventricular paced rhythms.

Use of the ECG for diagnosis of ischemic heart disease is more difficult in the setting of ventricular paced rhythms (VPRs). ST-segment/T-wave configuration are changed by the altered intraventricular conduction associated with ventricular pacing. The anticipated, or expected, morphology in patients with VPRs is one of QRS-complex-ST-segment to T-wave discordance. Several strategies are available to the physician to assist in the correct interpretation of the 12-lead ECG in patients with permanent ventricular pacemakers, including: a knowledge of the anticipated ST-segment-T-wave changes of VPRs and consequently the ability to recognize acute, ischemic morphologies; the performance of serial ECGs or ST-segment trend monitoring demonstrating dynamic changes encountered in acutely ischemic patients; a comparison with previous ECGs; and, if appropriate, an analysis of the native, underlying rhythm. The first strategy, an awareness of the anticipated ST-segment morphologies of VPRs, is the most important and not dependent on additional diagnostic testing, past medical records, or additional expertise in pacemaker function. Two cases are reported in which an analysis of the ECG in the setting of VPR assisted the treating physicians in establishing the correct diagnosis of acute myocardial infarction.