LAUSR

A 35-year-old gentlemanwith manifest preexcitation consistent with right posterolateral accessory pathway underwent EP study for recurrent palpitation. In view of underlying preexcitation the most likely diagnosis entertained for the narrow QRS tachycardia is an orthodromic AV reentrant tachycardia [AVRT]. On careful analysis it is noted that a premature P wave [*] is initiating the narrow QRS tachycardia with a PR jump. During the narrow QRS tachycardia distinct pseudo “S” pattern [*] in the inferior leads is evident [panel A] and it is consistent with typical AVNRT. With AVRT there is sequential atrio-ventricular activation and we expect an RP interval of more than 90 ms. Moreover, the RP interval is remaining fixed suggestive of RP or VA linking making AT less likely. (see Fig. 1) The intracardiac electrogram [EGM] during the initiation of tachycardia is provided in panel B. It confirms the observation of premature atrial beat [PAB] inducing the narrow QRS tachycardia