Prediction of ablation success of idiopathic premature ventricular contractions with an inferior axis using the twelve-lead electrocardiogram

FUNDING ACKNOWLEDGEMENTS: Type of funding sources: None. INTRODUCTION: Catheter ablation is the first line treatment for idiopathic premature ventricular contractions (PVCs) from the right ventricular outflow tract (RVOT) but not left ventricular outflow tract (LVOT). However, differentiating the two using the twelve-lead electrocardiogram (ECG) is challenging. As an alternative strategy to guide clinical decision-making, we sought to find ECG criteria that predict outcome of catheter ablation directly rather than focus only. METHODS: This observational single center study included patients undergoing an ablation procedure for idiopathic PVCs with an inferior axis (positive QRS in leads II, III and aVF) at Hannover Heart Rhythm Center between 2012 and 2020. Patients were excluded if no activation mapping was performed because of low PVC activity. A complete suppression of the index PVC at the end of the ablation procedure was considered as ablation success. PVC axis was estimated with the help of the hexaxial reference system, and as an objective control was also calculated measuring QRS voltages and using three formulas: Arctan (aVF/I), Arctan ((2*II-I)/(Sqr(3)*I)) and +/-Arctan ((2*aVF)/(Sqr(3)*I)). RESULTS: The analysis included 108 patients (53% male, age 53 ± 17 years) with a PVC count of 22063 ± 14426 /24h. The dominant PVC had Left Bundle Branch Block (LBBB) like morphology in 80%, a mean transition (TZ)-score of 2.3 ± 1.2 and a mean axis of 87 ± 15°, estimated with the help of the hexaxial system. There was no significant difference between axis as estimated with the help of the hexaxial system compared to calculation via any of the formulas (87 ± 14, 87 ± 12 and 86 ± 16°, respectively). Overall ablation success was 82%. Considering ablation outcome according to the identified PVC localization, 46 of 47 cases (97.9%) of RVOT focus and 38 of 39 cases (97.4%) of LVOT focus were successful. On the other hand, all 8 cases with a parahisian focus were not successful and only 4 of 14 cases (28.6%) with a CS/LV summit focus were successful. Two ECG criteria were found to predict ablation failure: a more leftward PVC axis (p=0.015), which was associated with a parahisian focus (p<0.001), and an early precordial transition compared to the QRS complex during AV-nodal conduction (p=0.016), which was associated with a CS/LV summit focus (p<0.001). Using ROC statistics, a cutoff value of 75° for PVC axis and of 2.75 for TZ-Score index predicted ablation success with a positive predictive value of 93% if neither parameter applied (prediction of ablation failure, if either applied, 53 %). CONCLUSION: Two ECG criteria – a more leftward PVC axis and an early precordial transition compared to sinus rhythm – predicted ablation failure and a parahisian or CS/LV summit focus. These parameters should be considered when evaluating a patient for catheter ablation of PVCs with an inferior axis.