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

Objectives. We studied two patients with latent, decremental atrioventricular (AV) fibers in whom pre-excitation could be demonstrated only during wide complex tachycardia. Background. The presence of decremental AV fibers participating in antidromic AV reentrant tachycardia is usually suspected by the presence of pre-excitation either in sinus rhythm or during atrial pacing. Methods. Two patients were referred for evaluation and treatment of wide complex tachycardia whose configuration suggested ventricular tachycardia that could be terminated with adenosine infusion. They underwent standard electrophysiologic studies. Results. Baseline AH and HV intervals were normal. No pre-excitation was noted with atrial overdrive at multiple sites or during atrial extrastimulation. Retrograde conduction was present with a sequence compatible with AV node conduction. Sustained wide complex tachycardia was induced with ventricular overdrive pacing. Late atrial premature depolarizations during tachycardia pre excited the subsequent ventricular activation. Earlier atrial premature depolarizations delayed the subsequent ventricular activation. In one patient, early atrial premature depolarizations terminated the tachycardia without activating the ventricle. In the other patient, spontaneous tachycardia termination was accompanied by ventriculoatrial block The earliest ventricular activation was 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 tachycardia utilizing a slow, decrementally conducting AV pathway. Conclusions. This is the first report describing the presence of latent, decremental accessory AV pathways in which conduction was manifest only during antidromic AV reentrant tachycardia. To differentiate these wide complex tachycardias from adenosine-sensitive ventricular tachycardia, we recommend that atrial premature depolarizations be applied during tachycardia to rule out the presence of a latent, decremental AV fiber even in patients who do not otherwise have pre-excitation with atrial pacing techniques.