TQ segment (baseline) alternans during Prinzmetal's variant angina.

In a study of 93 patients who met criteria for Prinzmetal's angina, alternans of the ST segment was observed in 28 of 93 patients (30%). In 8 of these 28 patients, a hitherto undescribed variant of alternans, namely alternation (larger than or equal to 1 mm shift in 2:1 pattern) in the amplitude of the baseline or TQ segment (TQ Alt) was observed. In all eight patients serious ventricular arrhythmias were noted, namely, ventricular fibrillation in two, ventricular tachycardia in four, and multiform or advanced ventricular ectopic activity in eight. The TQ Alt developed only after ST segment alternans occurred. It is postulated that the alternations of the ST and TQ segments are due to differences in current flows due to inhomogeneity of depolarization and repolarization of the action potential caused by ischemia. Furthermore, the associated arrhythmias observed are related to the inhomogeneous state initiated by the ischemia.