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Background:Identifying and targeting atrial substrate zones that are vulnerable to unidirectional block and slow conduction may be critical to improve the outcomes of atrial fibrillation (AF) ablation. A single extrastimulus in the ventricular tachycardia substrate is able to identify decrement evoked potentials (DEEP) that are targets for VT ablation. Whether this is true for the atrial tissue remains unexplored.Aim:1) To systematically analyze whether the DEEP are present in the atrial tissue and their locations after pulmonary vein isolation. 2) To assess their relationship with the underlying voltage.Methods:Consecutive patients with recurrent AF undergoing ablation were prospectively enrolled at 2 institutions. A biatrial voltage map was created and after pulmonary vein isolation (PVI). A drive train and an extrastimulus (atrial refractory period + 20ms) was delivered from an epicardial site (proximal CS) and an endocardial site (left atrial appendage (LAA) with a multipolar mapping catheter sequentially placed at 8 left atrial sites and 5 right atrial sites. Electrograms (EGMs) that showed a local delay in activation with the extrastimulus were tagged identified as DEEPs.Results:28 patients, 20 pers AF, mean age 66+/-9y, mean LA size 28+/-4cm2 were enrolled. Of 7800 EGMs analyzed, 5.13 % showed DEEPs (6.01% with CS pacing and 4.24% with LAA pacing, p=0.001). The mean local decrement seen was 25 ms. Most DEEPs (62.4%) were identified in sites with a normal EGM at baseline with preserved voltages. DEEPs were equally distributed within the regions mapped, but more common in the LA than in the RA (67.3% vs 32.7%, p=0.045). Patients with persistent AF had a higher proportion of DEEPs than patients with paroxysmal AF (5.6% vs 3.2%, p=0.015).Conclusions:In this study, DEEPs were more often identified when pacing from the proximal coronary sinus, were more common in patients with persistent AF and were distributed more often in the LA than in the RA and most commonly occurred in regions with normal voltages at baseline. Further follow-up will elucidate whether the presence of DEEPs have any influence of arrhythmia free outcomes and hence whether they have the potential to become a new target for AF substrate ablation in addition to PVI.