Alternans of the ST segment of T wave. A sign of electrical instability in Prinzmetal's angina.

In an effort to determine the incidence of ventricular arrhythmias associated with ST segments alternans, the patterns of ST segment and T-wave electrical alternans (STEA) were analyzed in 93 patients during spontaneous Prinzmetal's angina. Twenty-eight of 93 patients, or 30% (Group I), showed STEA during episodes of ST segment elevation. SIxty-five of 93 patients, or 70% (Group II), showed no alternans during episodes of ST segment elevation. In Group I, ventricular arrhythmias, defined as all ventricular ectopic activity greater than 5 beats per minute and complex Lown grades III to V, occurred during 52 of 55 episodes, or 95%; whereas in Group II, ventricular arrhythmias occurred in only 51 of 125 episodes, or 41% (p less than 0.01). The difference in the incidence of ventricular fibrillation (VF) or ventricular tachycardia (VT) in the two groups was more striking. VT or VF occurred in 20 of 55 in Group I (36%) versus 5 of 125 in Group II (4%). Although there were no significant differences in age or sex between Group I and II patients, there was a significant difference in the magnitude of the maximum ST segment elevation (5 mm in Group I versus 3 mm in Group II, p less than 0.01). This study demonstrates that the occurrence of STEA and T wave alternans frequently heralds the onset of ventricular arrhythmias in Prinzmetal's angina. Both the arrhythmias and the alternans occur during the time of maximal ST segment elevation.