VT ablation protocol
Our electrophysiological study protocol was already described in our previous work16. Briefly, electrophysiological study included the delivery of 1–3 extrastimuli during pacing at two basic cycle lengths (400 and 600 ms) from two right ventricular (RV) sites [RV apex (RVA) and RV outflow tract] and burst pacing. A target VT was defined as an induced sustained monomorphic VT or a clinically documented VT. Catheter ablation was performed using an irrigated ablation catheter (ThermoCool or ThermoCool SF or ThermoCool STSF; Biosense Webster, CA, or Coolpath or Tacticath; Abbott, MN) via a transvenous and/or retrograde transaortic approach and/or percutaneous epicardial approach. For patients with inducible hemodynamically tolerated monomorphic VT, CA was performed at sites with mid-diastolic potential, where pacing entrained the VT with concealed fusion, a post-pacing interval within 30 ms of the VT cycle length (VTCL), and a stimulus-to-QRS interval of 70% of the VTCL with or without using a three-dimensional (3D) electroanatomical (EA) mapping system (CARTO, Biosense Webster or Ensite, Abbott, MN). In cases in which the 3D EA mapping system had been used, bipolar endocardial voltage mapping of the left ventricle (LV) was performed during sinus or RV pacing rhythm. The low-voltage area was defined by voltage criteria ≤1.5 mV7,17–19. Then, substrate modification was additionally performed based on the abnormal electrograms: fragmented electrograms and delayed electrograms with the operator’s discretion.
For patients with inducible hemodynamically intolerant monomorphic VT, exit sites and VT channels had been identified and ablated on the basis of the pace mapping. Then, substrate modification was additionally performed based on the abnormal electrograms with the operator’s discretion.
When VT was not inducible at the beginning of the procedure, substrate modification based on the abnormal electrograms was implemented.
PES was repeated after VT ablation. Successful ablation was defined as non-inducibility of the target monomorphic VT at the end of the procedure. However, when VT was not inducible at the beginning of the procedure, PES after RF delivery was not performed.
Furthermore, among the procedures without PES at the end of the procedure, we evaluated the number of procedures without sufficient RF delivery because of the reasons of untested PES.