PO-05-226 ORTHODROMIC RECIPROCATING TACHYCARDIA RELYING ON ABERRANT CONDUCTION: NEED FOR A LAGER CIRCUIT

Abstract

Aberrant conduction during orthodromic reciprocating tachycardia (ORT) can prolong the ventriculo-atrial conduction time, which is found essential for the reentry in certain situations. To investigate the prevalence and different mechanism of aberrancy-dependent ORT. ORT cases relying on aberrancy from 220 cases in our center were searched using the following criteria: (1) Multiple episodes of ORT with aberrant conduction in ECG ; (2) No baseline BBB during sinus rhythm; (3) Absence of narrow QRS form during tachycardia unless isoproterenol used; (4) Restoration of bundle branch conduction giving rise to tachycardia termination or circuit alteration. ECGs and intracardiac tracings during study were carefully examined. 3 patients from 220 patients (1.4%) with ORT showed the phenomenon of dependence on aberrancy. Clinical tachycardia episodes of the patients were short in time. All accessory pathways (APs) were located at anterolateral regions of atrioventricular annulus. None of them had baseline bundle branch block. Creating functional bundle branch block was necessary to induce the tachycardias. In the first patient with ORT and left bundle branch block (LBBB), a late-delivered premature ventricular contraction (PVC) was able to advance the next A and reset the tachycardia, which was diagnostic for ORT with aberrancy. Meanwhile, left bundle branch conduction was restored which narrowed the next QRS complex. Tachycardia was then terminated by the advanced wavefront reaching the ventricular insertion site of AP which was refractory. In the second case, termination of the tachycardia was always preceded by a spontaneous LBBB restoration, with the V and subsequent A at MA advanced, suggesting anterograde block in the AV node. In the other case was, induction required both right BBB and slow pathway conduction. When isoproterenol was given, fast pathway recovered followed by BBB restoration, which made anterograde limb again switched to slow pathway. All pathways were successfully ablated during the procedure. All patients have been free of arrhythmias for at least 6 months. Extra transseptal time caused by aberrancy can be an integral part of ORT, which can explain the infrequent or late onset and unsustainable episodes of ORT in certain patients and is useful in understanding the circuit and localizing the pathway.