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

INTRODUCTION: 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. METHODS AND RESULTS: 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. CONCLUSION: 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.