Electrophysiological Study and Endocardial Ablation Procedure
All patients underwent a transthoracic echocardiography study to evaluate left ventricular ejection fraction (LVEF) and to look for potential ventricular aneurysm or intracardiac thrombi. The electrophysiological study was performed under general anesthesia. Intracardiac electrograms were recorded using a digital electrophysiological recording system (Prucka CardioLab, USA or EP-WorkMate St. Jude Medical, St. Paul, MN, USA). Three-dimensional electroanatomic mapping was guided by an EnSite NavX system (St. Jude Inc., St. Paul, MN, USA) or CARTO 3 system (Biosense Webster, Diamond Bar, CA, USA).
If the patient was in sinus rhythm (SR), an endocardial voltage map during SR was acquired using an ablation catheter (ThermoCool NaviStar, Biosense Webster, CA, USA or CoolFlex, St. Jude Inc., St. Paul, MN, USA). Low voltage zones (LVZ) were defined as amplitude between 0.5 and 1.5 mV. Late potentials and/or local fragmented ventricular potentials were also tagged. After voltage mapping, VT induction was attempted with programmed stimulation. For hemodynamically well tolerated VTs, local activation mapping was performed. In cases that were non-inducible or with hemodynamically poorly tolerated VTs, substrate modification was performed during SR. Low voltage areas, fragmented or late potentials and areas with matching pace-maps were targeted. Radiofrequency (RF) ablation was performed with a power of 30-45 W at a temperature limit of 45 °C. The acute procedural endpoint was defined as non-inducibility of VTs.