ANTIDROMIC TACHYCARDIA UTILIZING DECREMENTAL, LATENT ACCESSORY ATRIOVENTRICULAR FIBERS - DIFFERENTIATION FROM ADENOSINE-SENSITIVE VENTRICULAR-TACHYCARDIA

Objectives. We studied two patients with latent, decremental atriovent ricular (AV) fibers in whom pre-excitation could be demonstrated only during wide complex tachycardia. Background. The presence of decrement al AV fibers participating in antidromic AV reentrant tachycardia is u sually suspected by the presence of pre-excitation either in sinus rhy thm or during atrial pacing. Methods. Two patients were referred for e valuation and treatment of wide complex tachycardia whose configuratio n suggested ventricular tachycardia that could be terminated with aden osine infusion. They underwent standard electrophysiologic studies. Re sults. Baseline AH and HV intervals were normal. No pre-excitation was noted with atrial overdrive at multiple sites or during atrial extras timulation. Retrograde conduction was present with a sequence compatib le with AV node conduction. Sustained wide complex tachycardia was ind uced with ventricular overdrive pacing. Late atrial premature depolari zations during tachycardia pre excited the subsequent ventricular acti vation. Earlier atrial premature depolarizations delayed the subsequen t ventricular activation. In one patient, early atrial premature depol arizations terminated the tachycardia without activating the ventricle . In the other patient, spontaneous tachycardia termination was accomp anied by ventriculoatrial block The earliest ventricular activation wa s at the annulus in the posteroseptal region in one patient and at the left posterior region in the other. Atrioventricular node reentry and atrial tachycardia with bystander AV fibers were also excluded. These findings establish the diagnosis of antidromic AV reentrant tachycard ia utilizing a slow, decrementally conducting AV pathway. Conclusions. This is the first report describing the presence of latent, decrement al accessory AV pathways in which conduction was manifest only during antidromic AV reentrant tachycardia. To differentiate these wide compl ex tachycardias from adenosine-sensitive ventricular tachycardia, we r ecommend that atrial premature depolarizations be applied during tachy cardia to rule out the presence of a latent, decremental AV fiber even in patients who do not otherwise have pre-excitation with atrial paci ng techniques.