R/S Ratio in Lead III Predicts Successful Ablation of Ventricular Arrhythmias Originating in Para-Hisian Region

Abstract Objectives The aim of this study was to investigate the electrocardiographic characteristics of ventricular arrhythmias (VAs) originating near the His bundle (HB) and use the R/S ratio in lead III (RIII/SIII ratio) to predict successful ablation of para-Hisian VAs. Background Catheter ablation for idiopathic VAs near the HB is often challenging, and data are limited. Methods The present study included 134 consecutive patients undergoing catheter ablation of para-Hisian VAs. The electrocardiographic characteristics in these patients were retrospectively evaluated with successful ablation and failed ablation. Results Successful ablation was achieved in 115 (85.8%) of the 134 patients. There was no significant difference in QRS duration between the successful and the failed ablation groups. The ablation success rate was significantly lower for para-Hisian VAs with a predominantly positive R wave in lead III than those with a predominantly negative S wave in lead III. The significant factor associated with successful ablation was the RIII/SIII ratio. The RIII/SIII ratio ≤1.1 predicted the successful ablation of para-Hisian VAs with high sensitivity (80.9%) and specificity (94.7%). The RIII/SIII ratio of >1.2 had high sensitivity (100.0%) and specificity (82.8%) to predict the distance  Conclusions The RIII/SIII ratio was a helpful predictor of the successful ablation of VAs originating in the vicinity of the HB. This may be useful for planning ablation of para-Hisian VAs and minimizing the risk of inadvertent atrioventricular block.