VALUE OF ANALYSIS OF ST SEGMENT CHANGES DURING TACHYCARDIA IN DETERMINING TYPE OF NARROW QRS COMPLEX TACHYCARDIA

Objectives. Repolarization changes during narrow QRS complex tachycard ia were analyzed to differentiate the tachycardia mechanism and to gui de the preliminary location of the accessory pathway. Background. Noni nvasive determination of the mechanism of tachycardia is becoming incr easingly important in view of the role of catheter ablation techniques for the cure of supraventricular tachycardia. Methods. We analyzed 15 9 12-lead electrocardiograms during narrow QRS complex tachycardia to evaluate 1) the tachycardia cycle; and 2) ST segment depression or T w ave inversion, or both. Each patient underwent a complete electrophysi ologic evaluation, Results. There were 13 atrial tachycardias, 57 atri oventricular (AV) node reentrant tachycardias and 89 AV reciprocating tachycardias. The mean RR cycle did not differ among types of tachycar dia. ST segment depression >2 mm or T wave inversion, or both, was pre sent 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 tac hycardia distinct patterns of repolarization changes and P wave config uration,were associated with different sites of the accessory pathway. Conclusions. The presence of ST segment depression >2 mm or T wave in version, or both, during narrow QRS complex tachycardia suggests that AV reentry using an accessory pathway is the mechanism of the tachycar dia. The phenomenon may be the consequence of a distinct pattern of re trograde atrial activation, Analysis of repolarization changes can gui de preliminary localization of the accessory pathway even in the absen ce of ventricular preexcitation.