Antidromic Atrioventricular Re-Entrant Tachycardia via Left Anterolateral Accessory Pathway With Long Conduction Time

Left-sided atrioventricular accessory pathways (APs) with long anterograde conduction time are uncommon causes of wide-QRS tachycardia.

A 21-year-old woman presented with recurrent wide-QRS tachycardia with right bundle branch block morphology. Baseline electrocardiogram and intracardiac recordings showed no pre-excitation. Retrograde conduction over the AP was absent. Antidromic atrioventricular re-entrant tachycardia (AVRT) was inducible. During sinus rhythm, retrograde mapping at the left anterolateral mitral annulus identified a discrete AP potential. Radiofrequency ablation at this site eliminated the potential and rendered the tachycardia noninducible. The patient remained asymptomatic at the 1-year follow-up.

The findings support antidromic AVRT mediated by a short left anterolateral AP with long conduction time. Definitive decremental conduction was not proven owing to lack of atrial-insertion pacing or adenosine testing and absent coronary sinus activation changes. Surface electrocardiographic features favored pre-excited supraventricular tachycardia over ventricular tachycardia.

Left-sided APs with long conduction time can mediate antidromic AVRT. Targeting a discrete pathway potential at the suspected site guides successful ablation.