Incessant Narrow QRS Complex Tachycardia in a Patient With a Prior Ablation History

A 30-year-old woman with a history of prior ablation for a concealed left posteroseptal accessory pathway (AP) presented with incessant narrow QRS tachycardia, highlighting a rare complication of incomplete AP ablation.

Adenosine transiently terminated the tachycardia, which recurred immediately. Electrophysiology study confirmed orthodromic atrioventricular reentry tachycardia (AVRT) due to a slow-conducting AP at the previously ablated site. Three-dimensional mapping localized the AP to the left posteroseptal region, and radiofrequency ablation at the shortest VA interval successfully eliminated the arrhythmia.

This case illustrates incessant AVRT caused by an iatrogenic slow-conducting posteroseptal accessory pathway following incomplete ablation. Recognition of this mechanism is important to guide appropriate repeat ablation and prevent tachycardia-induced cardiomyopathy.