Narrow complex supraventricular tachycardia. What is the mechanism?

His-refractory premature ventricular contraction during supraventricular tachycardia that results in delay of next A is usually suggestive of a decremental accessory pathway (AP)-mediated orthodromic reciprocating tachycardia. Introduction Electrophysiological evaluation of supraventricular tachycardia using various maneuvers is routinely performed before the attempted ablation. A comprehensive knowledge about various maneuvers used during the electrophysiology study (EPS) is crucial for establishing the correct mechanism of the tachycardia before the ablation is performed. A nodal response can be seen in retrogradely conducting decremental pathway. It just implies the retrograde conduction is slow.