Introduction: The phenomenon of intermittent retrograde conduction over an accessory pathway (AP) is very rare. Methods: We report a case of AVRT without ventricular pre-excitation and arrhythmia recorded. Stepwise decremental pacing was delivered from RV apex. When the pacing CL was shortened to 400 ms, Retrograde ventriculoatrial (V-A) Wenckebach-type block appeard with the earliest atrial activation at the ostium of CS. The S1S2 interval was first set to 450ms and then reduced by 10ms and atrial-ventricular node ERP (AVNERP) occurred at 500ms/410ms. Results: Retrograde conduction over an AP was present only during ventricular pacing with a fast pacing rate (S1S1 300ms, S1S2 500ms/290ms) and narrow QRS tachycardia was induced by atrial programmed stimulation. The AP was ablated successfully in the end. Conclusion: It is suggested that careful evaluation by EPS should be applied during baseline study, especially in the case without arrhythmia recorded.

Premature ventricular contractions (PVCs) originating from anterior interventricular septum is frequent and can be cured by radiofrequency catheter ablation (RFCA). Left ventricular diverticulum (LVD) often correlates with ventricular tachyarrhythmias and produces a higher risk of sudden cardiac death. Here, we report the case of a 29-year-old woman with a rare combination of PVCs originating from anterior interventricular septum and LVD who successfully received RFCA.