Ablation of unmappable ventricular parasystole originating from the right ventricular outflow tract: a case report

BACKGROUND: When the coupling interval is matched, ventricular parasystole can form a stable fusion QRS complex with sinus rhythm. Ablation of a fusion QRS complex has been rarely reported and is unexpectedly difficult. CASE PRESENTATION: We describe a case of ventricular parasystole from muscle sleeves of the right ventricular outflow tract. The patient was a 54-year-old woman who was admitted to the hospital because of frequent palpitations for 3 months. Anti-arrhythmic drugs had been ineffective, and she had no history of cardiovascular disease. Because the fusion QRS complex interfered with the conventional mapping technique, we could not eliminate the ventricular parasystole successfully. RESULTS AND CONCLUSIONS: Finally, we used the reversed U curve method and found that the source of ventricular arrhythmia was in the right cusp according to the special local potential. A fusion QRS complex formed by ventricular parasystole and nodal ventricular activation make mapping and ablation difficult. The special local potential was the only evidence available to confirm the target of ablation satisfactorily.