Response to Letter Regarding Article, "Ablation of Persistent Atrial Fibrillation Targeting Low-Voltage Areas With Selective Activation Characteristics".

We thank Bartoletti et al for their comments on our novel approach for ablation of persistent atrial fibrillation (AF) targeting selective atrial low-voltage sites.1 Here we provide answers to their comments: 1. Left atrial substrate characterization using bipolar voltage mapping has been mostly performed in sinus rhythm (SR). However, only a single study compared high-density voltage maps of the left atrium during SR in patients (1) without history of AF versus (2) patients with paroxysmal AF versus (3) persistent AF, versus long-persistent AF.2 In this study, the authors report in patients without history of AF, bipolar voltage values during SR that exceed >2.5mV at all left atrial sites.2 In contrast, the bipolar voltages during SR were significantly reduced in patients with history of AF.2 Atrial arrhythmias develop at slow-conduction sites with increased myocardial fibrosis.1 Yet, these regions are not completely fibrotic or electrically silent. To our knowledge, no sharp cutoff value for low voltage has been found that includes all proarrhythmic sites and excludes normal tissue. During substrate mapping of scar-related ventricular tachycardias, the bipolar voltage threshold on …