Narrow QRS Tachycardia in a Patient with Spongiform Cardiopathy and Preexcitation: What is the Mechanism?

Abstract

Case SummaryA 19-year-old man diagnosed with spongiform cardiomyopathy and ventricular preexcitacion was referred to our hospital for electrophysiological (EP) testing after a syncopal episode. Baseline electrocardiogram (ECG) showed ventricular preexcitation consistent with the presence of a superior paraseptal, anteroseptal, accessory pathway (AP). After triple femoral vein puncture, a decapolar catheter was placed in the coronary sinus, a tetrapolar catheter in the His bundle region (with no clear His deflection recorded through the EP study), and a 4-mm-tip irrigated ablation catheter initially at the RV apex. Programmed atrial extrastimuli from the coronary sinus reproducibly induced nonsustained and sustained episodes of an irregular narrow QRS tachycardia with apparent atrioventricular dissociation in the surface ECG (Fig. 1). Intracardiac recording during ongoing tachycardia are also shown (Figs. 2 and 3). What is the involved mechanism? compared with RV apex. Programmed atrial extrastimuli repeatedly induced nonsustained and sustained runs of an irregular (cycle length 330-366 milliseconds) narrow QRS tachycardia (Fig. 1). Intracardiac recordings showed a narrow QRS tachycardia with more ventricular than atrial activations. Atrial activation was concentric at the coronary sinus and similar to the previous VA conduction. A progressive prolongation of the VA intervals until blockade consistently developed, suggesting a nodal retrograde Wenckebach sequence (Fig. 2). CommentaryThe association between noncompaction cardiomyopathy and the presence of APs has been described. 1 In the present case, the presence of retrograde VA block during tachycardia excludes the participation of the AP as the retrograde limb of the tachycardia circuit. The differential diagnosis of narrow complex tachycardia with VA block includes automatic junctional tachycardia (AJT), AVNRT with upper common pathway block and a nodofascicular tachycardia using the His-Purkinje system for antegrade conduction and the pathway for retrograde conduction.In our case, reproducible induction ruled out AJT. The onset of AJT is usually spontaneous with absence of critical AH delay and often requires catecholamines. 2We observed reproducible induction with premature atrial extraestimuli followed by long PR intervals and even with spontaneous atrial ectopic beats, which strongly favors the diagnosis of AV node reentry (Fig. 1). The degree of ventricular irregularity observed in our case would not be expected with JT. Moreover, during periods of more regular tachycardia, reset phenomena by sinus beats were repeatedly observed through the AV-node slow pathway, although due to the irregular nature of the tachycardia, a spontaneous change in cycle length cannot be completely excluded. Figure 3 shows how, during a retrograde Wenckebach sequence, a sinus beat timed only 52 milliseconds before QRS onset advances the next ventricular deflection (through a slow nodal pathway) without advancement of the immediate QRS. Reset of the tachycardia by atrial depolari...

Atypical Response to Diagnostic Maneuvers in a Narrow QRS Tachycardia: What is the Mechanism?

“…A), which indicates that a slow AV nodal pathway is acting as the antegrade limb of the tachycardia and supports the diagnosis of AVNRT. As AV nodal slow pathway is not involved in JET, advancement or delay of the next His signal via extrastimuli (or spontaneous atrial ectopic beats) timed to His refractoriness is not possible in this tachycardia, although spontaneous cycle length changes may mimic this phenomenon.…”