BACKGROUND: Bedside ST segment monitors analyze only one precordial lead and one, two or three limb leads. The precordial lead V1 (or V6 if V1 is not feasible) has been recommended for bedside monitoring because of its value in diagnosing cardiac rhythms with a wide QRS complex. Thus, the remaining lead choices for ST monitoring are limited to the six limb leads. PURPOSE: To determine which of the limb leads in conjunction with V1 or V6 provides the greatest sensitivity for myocardial ischemia, a study was undertaken. METHOD: A total of 30 vessel-unique ischemic episodes were analyzed prospectively using continuous 12-lead electrocardiographic recordings in patients with acute myocardial infarction (n = 2) and patients undergoing coronary angioplasty (n = 25). RESULTS: Ischemic changes were evident in all cases using the full 12-lead electrocardiogram. Right coronary artery-related ischemia was detected in all cases using a single-lead III or aVF. In the group as a whole, the best combinations were: V1 + aVF, V1 + III, V6 + III, and V6 + aVF. Two patients developed sudden coronary artery reocclusion in the cardiac care unit after successful angioplasty. In both, leads identified in the cardiac catheterization laboratory as sensitive for recording ischemia were excellent choices for detection of reocclusion in the cardiac care unit. CONCLUSIONS: 12-lead electrocardiogram recordings during coronary angioplasty balloon inflation provide excellent guidance for postprocedure lead selection decisions. The most valuable limb leads for detecting ischemia due to abrupt artery closure are leads III and aVF, either of which is more sensitive than the routinely monitored lead II. The precordial leads valuable for arrhythmia monitoring, V1 and V6, are seldom sensitive in detecting ischemia in these patients.

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