Objectives. Repolarization changes during narrow QRS complex tachycardia were analyzed to differentiate the tachycardia mechanism and to guide the preliminary location of the accessory pathway. Background. Noninvasive determination of the mechanism of tachycardia 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 tachycardia to evaluate 1) the tachycardia cycle; and 2) ST segment depression or T wave inversion, or both. Each patient underwent a 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 tachycardia (57%) than in AV node tachycardia (25%). The magnitude of ST segment depression was greater in AV reciprocating tachycardia than in AV node tachycardia (mean ± SD 1.3 ± 1.6 vs. 0.7 ± 0.8 mm, p <0.005). In AV reciprocating tachycardia 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, during narrow QRS complex tachycardia suggests that AV reentry using an accessory pathway is the mechanism of the tachycardia. The phenomenon may be the consequence of a 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.
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