INTRODUCTION
Although pulmonary vein (PV) isolation (I) remains a cornerstone of any AF ablation (1,2,3 ), other anatomical regions of the left atrium (LA), i.e. non-PV substrates, are involved in AF, especially in persistent (Ps) AF (4,5 ). High density (HD) endocardial voltage mapping by means of multipolar catheters and 3d electro-anatomical systems (3d-S) has been increasingly used in clinical practice to identify both left ventricular (6) and LA anatomical areas of low-voltage (LV) electrical activity (7,8) , which is commonly considered a marker of atrial fibrosis (9 ). LA substrate modification by targeting LV zones is an ablation strategy that, in addition to PVI, tries to erase arrhythmogenic mechanisms harbored in such tissue (7 ,10 ). However, bipolar recordings have a limited ability to identify LV electrical activity, as they are subject to various influences, such as the bipole orientation expressed by the angle of attack and the activation wavefront; this can mean that electrical signals may not be recorded even when they are present (11 ). Recent reports have described experiences of the use of new catheters with omnipolar recording capacity which do not seem to be affected by the negative influences described above with regard to bipolar HD maps (12,13). The aim of the present study was to perform a post-hoc analysis in patients undergoing PVI, in order to evaluate the incidence of non-PV substrates detected by different diagnostic catheter technologies, including multipolar (MC), omnipolar (OC), and circular mapping catheters (CMC), and by means of qualitative and quantitative analysis of LV on applying various voltage ranges.