Paradoxical delay in accessory pathway conduction during long R-P′ tachycardia after interpolated ventricular premature complexes

The introduction of a ventricular premature complex (VPC) into reciprocating tachycardia is a technique used to confirm the presence of an accessory atrioventricular (AV) pathway.^1-3 Retrograde atrial preexcitation after a VPC introduced during reciprocating tachycardia when the His bundle is refractory to retrograde conduction is evidence that an accessory pathway is present.³ The failure of an appropriately timed VPC to alter the timing of atrial activation implies that either an accessory pathway conducting in the retrograde direction is not present or that the accessory pathway is relatively far from the site of premature stimulation.³ This latter possibility can occur when VPCs are inserted into the right ventricular apex in patients with a left lateral accessory pathway. The finding that an accessory pathway can show a paradoxical delay in retrograde atrial activation during reciprocating tachycardia with this maneuver has not been described. We report a patient with a posterior septal accessory pathway with decremental conduction properties characteristic of the "permanent form of junctional reciprocating tachycardia." Paradoxical delay in retrograde atrial activation was observed after the introduction of a VPC into reciprocating tachycardia when the His bundle was refractory.