Alternans of the ST segment in Prinzmetal's angina.

Abstract

Alternans of the elevated ST segment (STEA) was found in 8 of 21 patients (38%) with Prinzmetal''s variant angina. In addition to STEA, all 8 patients had varying cardiac arrhythmias: multiple premature ventricular depolarizations in 8, ventricular tachycardia in 5 and ventricular fibrillation in 3. There was no consistent temporal relationship between the occurrence of STEA and the cardiac arrhythmias. Alternans occurred during periods when no arrhythmias were present. All 8 patients underwent coronary angiography. Spontaneous coronary artery spasm was documented angiographically in 3 patients including 2 who had minimal or no coronary atheroslerotic disease. Six patients had severe, fixed, occlusive coronary artery disease. Possible mechanisms for STEA include failure of regions of myocardium to depolarize on alternate beats due to variation in conduction and refractoriness between ischemic and nonischemic zones of myocardium, and electrical alternans of the transmembrane action potential during phases 2 and 3 (repolarization) caused by changes in the rate and extent of electrolyte transfer across cell membranes during ischemia. STEA is possibly an ECG sign in the surface ECG of a dysequilibrium of refractory periods during ischemia and reflects an unstable electrical state of the myocardium.