Epicardial ablation may not be necessary in all patients with arrhythmogenic right ventricular dysplasia/cardiomyopathy and frequent ventricular tachycardia: author’s reply

We thank Dr Mussigbrodt and colleagues for their interest in on our study.1,2 From their observational and retrospective study, Mussigbrodt et al.3 propose that in arrhythmogenic right ventricular dysplasia (ARVC) patients undergoing ventricular tachycardia (VT) substrate ablation epicardial approach should be performed only if VTs are still inducible after thorough endocardial ablation. Using this strategy, they report a recurrence rate of 44% after a mean follow-up of 31.1 ± 27.4 months, which was similar to that obtained in the group of patients that underwent endo-epicardial approach (41%). We surely agree with Mussigbrodt et al. that all ARVC patients may not benefit the same from epicardial approach. However, in our opinion, the decision to perform epicardial approach should not be based only on VT inducibility after endocardial ablation. Prior studies have shown that isolated endocardial ablation in ARVC patients has suboptimal results, yielding recurrence rates around 50–75%.4 In contrast, first-line combined endo-epicardial substrate ablation obtained a significantly lower rate of VT recurrence (17.6% in the subgroup of ARVC patients, including those with left ventricular involvement) at long-term follow-up in our prospective multicenter study2. These good results are due to the particular substrate distribution pattern observed in ARVC, with predominant epicardial involvement. Consistent with the described epicardium-to-endocardium progression pattern, our study showed more extensive involvement of epicardium than endocardium. Indeed, isolated epicardium involvement with completely normal endocardial bipolar map was observed in 26.4% of patients. Concordantly, Philips et al.5 showed that the majority of VT circuits were epicardial in a series of 30 ARVC patients, 60% of them requiring only epiablation. Another important finding of our work was the fact that among ARVC patients with endocardial right ventricular (RV) involvement, a negative correlation was observed between endocardial scar area and epicardial arrhythmic substrate extension, suggesting that patients with more advanced stage of ARVC (thus, with a more extensive involvement of the RV endocardium) tend to have less arrhythmic substrate in the epicardium due to the progressive fibrofatty replacement at this level. Consistently with this hypothesis, patients at an advanced stage of ARVC in terms of substrate progression, and therefore with an extensive endocardial scar and a bipolar vs. unipolar low voltage area ≥0.23, required the most of radiofrequency applications be delivered at the endocardium. Considering these data, we believe that the decision to perform epicardial approach in ARVC patients should be based on the individual substrate distribution pattern rather than VT inducibility after endocardial ablation. Therefore, we propose that patients having an endocardial bipolar vs. unipolar ratio <0.23 should undergo first-line combined endo-epicardial approach. On the other hand, in patients with extensive endocardial scar area (bipolar vs. unipolar ratio ≥0.23), which represented 20% of ARVC patients in our study cohort, the indication of epicardial approach should be assessed more cautiously and based on persistence of VT inducibility after endocardial substrate eliminatoin. This strategy should be validated in further studies.