Value of analysis of ST segment changes during tachycardi in determining type of narrow QRS complex tachycardi

Objectives. Repolarization changes during narrow QRS complex tachycardi were analyzed to differentiate the tachycardi mechanism and to guide the preliminary location of the accessory pathway. Background. Noninvasive determination of the mechanism of tachycardi is becoming increasingly important in view of the role of catheter ablation techniques for the cure of supraventricular tachycardia. Methods. We analyzed 159 12-lead electrocardiograms during narrow QRS complex tachycardi to evaluate 1) the tachycardis cycle; and 2) ST segment depression or T wave inversion, or both. Each patient underwent complete electrophysiologic evaluation. Results. There were 13 atrial tachycardias, 57 atrioventricular (AV) node reentrant tachycardias and 89 AV reciprocating tachycardias. The mean RR cycle did not differ among types of tachycardia. ST segment depression >2 mm or T wave inversion, or both, was present more often in AV reciprocating tachycardi (57%) than in AV node tachycardi (25%). The magnitude of ST segment depression was greater in AV reciprocating tachycardi than in AV node tachycardi (mean ± SD 1.3 ± 1.6 vs. 0.7 ± 0.8 mm, p < 0.005). In AV reciprocating tachycardi distinct patterns of repolarization changes and P wave configuration were associated with different sites of the accessory pathway. Conclusions. The presence of ST segment depression > 2 mm or T wave inversion, or both, durig narrow QRS complex tachycardi suggests that AV reentry using an accessory pathway is the mechanism of the tachycardia. The phenomenon may be the consequence of distinct pattern of retrograde atrial activation. Analysis of repolarization changes can guide preliminary localization of the accessory pathway even in the absence of ventricular preexcitation.