Introduction:
Catheter ablation (CA) of premature ventricular contractions (PVC), originating from parahisian region, can be challenging due to the high risk of jatrogenic atrioventricular (AV) block and lower short- and long-term success rate.

The aim:
We present a case of parahisian PVC ablated using reversed S-curve approach with ablation catheter placed under the septal leaflet of the tricuspid valve.

A 68 -year-old male patient with highly symptomatic frequent PVCs (20% PVC burden in 24 Holter ECG), refractory to antiarrhythmic therapy, was referred to our clinic for CA. The 12-lead ECG revealed frequent monomorphic PVCs with relatively narrow QRS (120ms), LBBB pattern, inferior axis, R/S transition in V3 (Fig.1A, PVC A), highly suggestive for parahisian origin.

A high-density mapping of the right ventricle (RV) and coronary sinus (CS), using CARTO 3 system (Biosense Webster, Diamond bar, USA), was performed via multipolar mapping catheter (DECANAV, Biosense Webster), using a steerable sheath. Pattern matching of PVC and sinus rhythm beats were simultaneously performed using local activation time (LAT) hybrid (CONFIDENSE module, Biosense Webster). The earlies activation site was detected at the site of registration of His potentials (Fig.1B). Ablation catheter was positioned under the tricuspid valve (TV), retrograde, using reversed S-curve (Fig. 2A). At the earliest site (38 ms to onset QRS, RF- ablation (30 Watts) immediately abolished the PVC. After 5 minutes of observation period PVC reappeared with slightly different morphology (PVC B), suggesting the same parahisian origin with exit site caudal from the His site. (Fig. 1C) Ablation at the site of earliest activation (26ms to onset QRS) using inverted S-curve (30W) (Fig.2B) finally eliminated the PVC.

No PVCs were observed during the waiting period of 30 minutes. On short-term follow-up (30 days), no recurrence of PVC occurred.

Conclusion: the retrograde approach using reversed S-curve for ablation of challenging CA of parahisian PVCs is safe and effective.

Figure 1(A) Baseline ECG showing PVC (3^rd beat, red star) with inferior axis, R/S transition in V3, speed 25 mm/s. (B) Activation map of the RV (PVC A) with earliest activation site. (C) Activation map of the RV (PVC B) with earliest activation site.

Figure 2 (A) position of the ablation catheter (retrograde, under the tricuspid valve, S-curve) by the ablation of PVC A. (B) Reversed S-kurve of the ablation catheter by the ablation of PVC B. 

Yellow visitags-His, red visitags- ablation points. White arrow- ablation catheter. Yellow arrow- His catheter.