Paroxysmal Supraventricular Tachycardia With Ventriculoatrial Block and QRS Duration Shortening: What Is the Mechanism?

Abstract

Case SummaryA 45-year-old man with normal heart structure and function underwent an electrophysiology study for recurrent palpitations. Catheters were placed in the coronary sinus, in the right ventricular apex, and at the His bundle. The baseline electrocardiogram was normal with subtle preexcitation and normal intervals (A-H 87 milliseconds, H-V 50 milliseconds). There was poor VA conduction and evident VA dissociation during retrograde conduction studies. Atrial double extra-stimuli showed progressive prolongation of the A-H interval with induction of a narrow complex tachycardia of cycle length 440 milliseconds (Fig. 1). The QRS shortened at the onset of tachycardia with subtle changes in the surface electrocardiogram. There was VA dissociation during the tachycardia. A premature ventricular complex (PVC) during His refractory advanced the subsequent His and reset the tachycardia (Fig. 2).What is the mechanism of this tachycardia and why was there shortening of the QRS duration? DiscussionVentriculoatrial dissociation during a narrow complex supraventricular tachycardia is an uncommon occurrence, and on a background of ventriculoatrial conduction block differential diagnoses include:(1) Junctional tachycardia (2) Atrioventriculoventricular nodal reentrant tachycardia (AVNRT) (3) Intra-Hisian reentry