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Funding Acknowledgements Type of funding sources: None. Background In a previous study it was demonstrated that an electrophysiological triad was able to identify critical isthmus in atrial flutter (AFL) patients. This triad is based in the Carto® electroanatomical mapping (EAM) version 7, which displays a histogram of the local activation times (LAT) of the tachycardia cycle length (TCL), in addition to the activation and voltage maps. Purpose This study aimed to prospectively assess the ability of a modified electrophysiological triad to identify and localize the ventricular tachycardia’s (VT) channels and entrance zones during sinus rhythm mapping. Methods Prospective analysis of a unicentric registry of individuals who underwent ischemic VT ablation with Carto® EAM, all in sinus rhythm. All patients with non-ischemic etiology, lack of high-density EAM or lack of mapping in any of the left ventricle walls or structures were excluded. Areas of late potentials and possible channels of re-entry were compared to a modified electrophysiological triad constituted by: areas of low-voltage ( Results A total of 14 patients (14 men, median age 70 IQR 64-78 years) were included. All patients presented with ischemic VT and 86% had a previous inferior myocardial infarction. The median number of collected points were 1733 (IQR 1363─2729). All sinus rhythm maps presented with at least 1 LAT-Valley in the analysed histograms. All arrhythmias were effectively treated after undergoing radiofrequency in the LAT-Valley location, either by blocking the channel entrances or scar homogenization ablation strategy. Also, the pre-valley bar in the histogram marked all the channel entrances in the scar borders. No patient had relapse after a clinical follow up of over 6 months. Conclusion In a prospective analysis, a modified electrophysiological triad was able to identify the scar channels in sinus rhythm in all patients. The pre-valley bar in the histogram disclosed the channel entrances. Further studies are needed to assess the usefulness of this algorithm to simplify catheter ablation and improve clinical outcomes.

Funding Acknowledgements Type of funding sources: None. Introduction Pulmonary veins (PV) ostia were previously identified as the left atrium (LA) areas with the shortest refractory period during sinus rhythm. Pulmonary veins isolation (PVI) became standard of care, but clinical results are still suboptimal. Currently, atrial fibrillation (AF) cycle length mapping (CLM) is possible due to a special tool of the Carto® electroanatomical mapping, which identifies areas in the left atria with shortest refractory period, during AF. Purpose Using this new EAM feature, our study aimed to assess the relationship between short refractory period LA areas and left atrial volume and AF type, known predictors of AF relapse. Methods Retrospective analysis of an unicentric registry of individuals with symptomatic drug-refractory AF who underwent PVI AF ablation with Carto® EAM. CLM was performed. CL maps were created with a high-density mapping Pentaray® catheter before and after PVI. We assessed areas of short cycle length (SCL) (defined as 120 to 250ms), and their relationships with complex fractionated atrial electrograms (CFAE), and low-voltage zones (from 0.1 to 0.3mV). Results A total of 35 patients (21 men, median age 62 IQR 53-71 years) were included. Most patients presented with persistent AF (n=23, 66%), and 8 patients (23%) had a previous PVI. The mean shortest measured cycle length in AF was 134ms (SD ± 23ms). There was a negative correlation between LA volume and SCL areas after PVI (Spearman Correlation coefficient [ρ] = - 0.47, P = 0.037). There was no correlation between LA volume and SCL areas before the PVI procedure (ρ = -0.06, P = 0.776), nor between AF type and SCL (ρ = -0.118, P = 0.620). All patients presented areas of SCL located in the PVs or their insertion, 76% in the posterior/roof region adjacent to the left superior pulmonary vein (LSPV) and 76% in the anterior region of the wall adjacent to the right superior pulmonary vein (RSPV). These two areas remained the fastest even after PVI. The anterior mitral region rarely presented SCL (16%). SCL were related to low-voltage areas in 93% and were adjacent to CFAE in 84% of the cases. Low-voltage areas and CFAE were more frequent and had a larger LA dispersion than SCL. Conclusion Our study shows that LA volume, not AF type, is correlated with remaining SCL areas after a pulmonary vein isolation procedure. This finding suggests a possible causal link between increased LA volume and AF relapse post-PVI. More studies are needed to assess the role of the SCL areas as a potential ablation target and their impact on AF ablation outcomes.

Funding Acknowledgements Type of funding sources: None. Introduction In a previous retrospective study it was demonstrated that an electrophysiological triad was able to identify critical isthmus in atrial flutter (AFL) patients. This triad is based in the Carto® electroanatomical mapping (EAM) version 7, which displays a histogram of the local activation times (LAT) of the tachycardia cycle length (TCL), in addition to the activation and voltage maps. This study aimed to prospectively assess the ability of an electrophysiological triad to identify and localize the AFL’s critical isthmus. Methods Prospective analysis of a unicentric registry of individuals who underwent left AFL ablation with Carto® EAM. All patients with non-left AFL, lack of high-density EAM, less than 2000 collected points or lack of mapping in any of the left atrium walls or structures were excluded. Ablation sites of arrhythmia termination were compared to an electrophysiological triad constituted by: areas of low-voltage (0.05 to 0.3mV), sites of deep histogram valleys (LAT-Valleys) with less than 20% density points relative to the highest density zone and a prolonged LAT-Valley duration that included 10% or more of the TCL. The longest LAT-Valley was designated as the primary valley, while additional valleys were named as secondary. Results A total of 12 patients (9 men, median age 72 IQR 67-75 years) were included. All patients presented with left AFL and 67% had a previous atrial fibrillation and/or flutter ablation. The median TCL and number collected points were 250 (230─290) milliseconds and 3150 (IQR 2340─3870) points, respectively. All AFL presented with at least 1 LAT-Valley in the analysed histograms, which corresponded to heterogeneous low-voltage areas (0.05 to 0.3mV) and encompassed more than 10% of TCL. Eleven of the 12 patients presented with at least 1 secondary LAT-Valley. All arrhythmias were effectively terminated after undergoing radiofrequency ablation in the primary or the secondary LAT-Valley location. Conclusion In a prospective analysis, an electrophysiological triad was able to identify the AFL critical isthmus in all patients. Further studies are needed to assess the usefulness of this algorithm to improve catheter ablation outcomes.

Introduction Catheter ablation outcomes for drug-resistant ventricular tachycardia (VT) in nonischemic cardiomyopathy (NICM) are suboptimal when compared to ischemic cardiomyopathy. We aimed to analyse the long-term efficacy and safety of percutaneous catheter ablation in this subset of patients. Methods Single-center observational retrospective registry including consecutive NICM patients who underwent catheter ablation for drug-resistant VT during a 10-year period. The efficacy endpoint was defined as VT-free survival after catheter ablation, while safety outcomes were defined by 30-days mortality and procedure-related complications. Independent predictors of VT recurrence were assessed by Cox regression. Results In a population of 68 patients, most were male (85%), mean left ventricular ejection fraction (LVEF) was 34±12%, and mean age was 58±15 years. All patients had an implantable cardioverter-defibrillator. Twenty-six (38%) patients underwent epicardial ablation (table 1). Over a median follow-up of 3 years (IQR 1–8), 41% (n=31) patients had VT recurrence and 28% died (n=19). Multivariate survival analysis identified LVEF (HR= 0.98; 95% CI 0.92–0.99, p=0.046) and VT storm at presentation (HR=2.38; 95% CI 1.04–5.46, p=0.041) as independent predictors of VT recurrence. The yearly rates of VT recurrence and overall mortality were 21%/year and 10%/year, respectively. No patients died at 30-days post-procedure, and mean hospital length of stay was 5±6 days. The complication rate was 7% (n=5, table 1), mostly in patients undergoing epicardial ablation (4 vs 1 in endocardial ablation, P=0.046). Conclusion LVEF and VT storm at presentation were independent predictors of VT recurrence in NICM patients after catheter ablation. While clinical outcomes can be improved with further technical and scientific development, a tailored endocardial/epicardial approach was safe, with low overall number of complications and no 30-days mortality. Funding Acknowledgement Type of funding sources: None.

Funding Acknowledgements Type of funding sources: None. INTRODUCTION Catheter ablation outcomes for drug-resistant ventricular tachycardia (VT) in nonischemic cardiomyopathy (NICM) are suboptimal when compared to ischemic cardiomyopathy. We aimed to analyse the long-term efficacy and safety of percutaneous catheter ablation in this subset of patients. METHODS Single-center observational retrospective registry including consecutive NICM patients who underwent catheter ablation for drug-resistant VT during a 10-year period. The efficacy endpoint was defined as VT-free survival after catheter ablation, while safety outcomes were defined by 30-days mortality and procedure-related complications. Independent predictors of VT recurrence were assessed by Cox regression. RESULTS In a population of 68 patients, most were male (85%), mean left ventricular ejection fraction (LVEF) was 34 ± 12%, and mean age was 58 ± 15 years. All patients had an implantable cardioverter-defibrillator. Twenty-six (38%) patients underwent epicardial ablation (table 1). Over a median follow-up of 3 years (IQR 1-8), 41% (n = 31) patients had VT recurrence and 28% died (n = 19). Multivariate survival analysis identified LVEF (HR= 0.98; 95%CI 0.92-0.99, p = 0.046) and VT storm at presentation (HR = 2.38; 95%CI 1.04-5.46, p = 0.041) as independent predictors of VT recurrence. The yearly rates of VT recurrence and overall mortality were 21%/year and 10%/year, respectively. No patients died at 30-days post-procedure, and mean hospital length of stay was 5 ± 6 days. The complication rate was 7% (n = 5, table 1), mostly in patients undergoing epicardial ablation (4 vs 1 in endocardial ablation, P = 0.046). CONCLUSION LVEF and VT storm at presentation were independent predictors of VT recurrence in NICM patients after catheter ablation. While clinical outcomes can be improved with further technical and scientific development, a tailored endocardial/epicardial approach was safe, with low overall number of complications and no 30-days mortality. Abstract Figure.

Introduction Twenty years ago, pulmonary veins (PV) ostia were identified as the left atrium (LA) areas with the shortest refractory period during sinus rhythm. Pulmonary veins isolation (PVI) became standard of care, but clinical results are still suboptimal. Today, a special tool using the Carto® electroanatomical mapping (EAM) allows for AF cycle length mapping (CLM), to identify the areas in the left atria with shortest refractory period, during atrial fibrillation. Using this EAM tool, our study aimed to find the LA areas with the shortest refractory period to better recognize electrical targets for catheter ablation. Methods Retrospective analysis of an unicentric registry of individuals with symptomatic drug-refractory AF who underwent PVI with Carto® EAM. CLM was performed with a high-density mapping Pentaray® catheter before and after PVI and in 4 redo procedures. We assessed areas of short cycle length (SCL) (defined as 120 to 250ms), and their relationships with complex fractionated atrial electrograms (CFAE), and low-voltage zones (from 0.1 to 0.3mV). Results A total of 18 patients (8 men, median age 63 IQR 58–71 years) were included. Most patients presented with persistent AF (n=12, 67%), and 4 patients (22%) had a previous PVI. The mean shortest measured cycle length in AF was 140ms (SD ±27ms). All patients presented areas of SCL located in the PVs or their insertion, 70% in the posterior/roof region adjacent to the left superior pulmonary vein (LSPV) (figure 1) and 60% in the anterior region of the right superior pulmonary vein (RSPV). These two areas remained the fastest even after PVI. The anterior mitral region rarely presented SCL (17%). SCL were related to low-voltage areas in 94% and were adjacent to CFAE. Low-voltage areas and CFAE were more frequent and had a larger LA dispersion than SCL. Conclusion We confirmed in 3D mapping that PVs are the LA zones with shortest refractory period, not only in sinus rhythm but also during AF. The persistence of SCL areas in the border zones of the PVI lines suggest the benefit of a more extensive CLM guided ablation. Larger studies are needed. Funding Acknowledgement Type of funding sources: None. Short cycle length mapping

Background Epicardial adipose tissue (EAT) has recently been shown to be associated with the presence, severity, and recurrence of atrial fibrillation (AF). Although the pathophysiological mechanisms underlying this association remain to be established, several hypotheses have been put forward, including direct adipocyte infiltration, oxidative stress, and the secretion of adipokines causing inflammation and fibrosis of atrial tissue. We hypothesized that the volume of EAT and the amount of left atrium (LA) fibrosis assessed by non-invasive imaging would be significantly correlated in patients with AF, and that both would predict time to relapse after pulmonary vein isolation (PVI). Methods Sixty-eight patients with AF being studied for a first PVI procedure underwent both cardiac computerized tomography (CT) and cardiac magnetic resonance (CMR) within less than 48h. EAT was quantified on contrast-enhanced CT images. LA fibrosis was quantified on isotropic 1.5mm 3D delayed enhancement CMR for image intensity ratio values >1.20. Radiofrequency PVI was performed using an irrigated contact force-sensing ablation catheter, guided by electroanatomical mapping. After PVI, patients were followed for AF recurrence, defined as symptomatic or documented AF after a 3-month blanking period. Pearson's correlation coefficient was used for gauging the correlation between EATLM volume and LA fibrosis. The relationship between these two variables and time to AF recurrence was assessed by Cox regression. Results Most of the 68 patients (46 men, mean age 61±12 years) had paroxysmal AF (71%, n=48). The mean body mass index (BMI) was 28.0±4.0 kg/m2. Patients had a median EATLM volume of 2.4 cm3/m2 [interquartile range (IQR) 1.6–3.2 cm3/m2], and a median estimated amount of LA fibrosis of 8.9 g (IQR 5–15 g), corresponding to 8% (IQR 5–11%) of the total LA wall mass. The correlation between EATLM and LA fibrosis was statistically significant but weak (Pearson's R = 0.38, P=0.001) – Figure 1. During a median follow-up of 22 months (IQR 12–31), 31 patients (46%) suffered AF recurrence. Four predictors of relapse were identified in univariate Cox regression: EATLM (HR 2.19, 95% CI 1.65–2.91, P Conclusion The weak correlation between EAT and LA suggests that LA fibrosis is not the main mechanism by which EAT and AF are linked. EAT was more strongly associated with AF recurrence than LA fibrosis, which supports the existence of other, more important mediators between EAT and this arrhythmia. Correlation between EAT and LA Funding Acknowledgement Type of funding source: None

Background Epicardial adipose tissue has been implicated in the pathophysiology of atrial fibrillation (AF), but its relevance to clinical practice remains uncertain. The aim of this study was to compare the performance of the amount of epicardial fat with previously published clinical scores of AF-relapse risk after pulmonary vein isolation (PVI). Methods We assessed 575 patients (354 men, age 61±11 years, 449 paroxysmal AF) with symptomatic AF undergoing cardiac CT prior to a PVI procedure. Epicardial fat was quantified on contrast-enhanced images using a new simplified semi-automated method. The study endpoint was symptomatic and/or documented AF recurrence at 12 months. Epicardial fat was compared against the following scores: MB-LATER, APPLE, DR-FLASH, and ATLAS. Results Median follow-up was of 22 months (IQR 12–35), 232 patients relapsed, 130 patients (27%) within the first 12 months. After adjustment for BMI and other univariate predictors of relapse, three variables emerged independently associated with time to AF recurrence: non-paroxysmal AF (HR 2.03, 95% CI: 1.53–2.69, p Conclusion Pericardial fat volume is a strong independent predictor of AF relapse after PVI, outperforming clinical scores of post-PVI AF. The underlying mechanisms of this association deserve further study. ROC Curve Analysys Funding Acknowledgement Type of funding source: None

Background Patients with ischemic (IHD) and nonischemic (NICM) dilated heart disease and reduced left ventricular ejection fraction are at increased risk of ventricular tachycardias (VTs) or sudden cardiac death. VT catheter ablation is an invasive treatment modality for antiarrhythmic drugs-resistant VT that reduces arrhythmic episodes, improves quality of life and improves survival in patients with electrical storm. Direct comparison of the outcomes from combined and non-combined endoepicardial ablations is limited by patient characteristics, follow-up durations, protocols heterogeneity and scarcity of randomized trials. We aim to investigate the long-term clinical outcomes of these 2 strategies in the IHD and NICM populations. Methods Multicentric observational registry including 316 consecutive patients who underwent combined (C-ABL) and non-combined (NC-ABL) endoepicardial ventricular tachycardia (VT) ablation for drug-resistant VT between January 2008 and July 2019. Chagas' disease patients were excluded. Primary and secondary efficacy endpoints were defined as VT-free survival and all-cause death after ablation. Safety outcomes were defined by 30-days mortality and procedure-related complications. Results Most of the patients were male (85%), with IHD (67%) and a mean age of 63±13 years. During a mean follow-up of 3±2 years, 117 (37%) patients had VT recurrence and 73 (23%) died. Multivariate survival analysis identified storm (ES) at presentation (HR=2.17; 95% CI 1.44–3.25), IHD (HR=0.53, 95% CI 0.36–0.78), left ventricular ejection fraction (LEVF) (HR=0.97, 95% CI 0.95–0.99), New York Heart Association (NYHA) functional class III or IV (HR=1.79, 95% CI 1.13–2.85) and C-ABL (HR=0.49, 95% CI 0.27–0.92) as independent predictors of VT recurrence. In 135 patients undergoing two or more ablation procedures only C-ABL (HR=0.36, 95% CI 0.17–0.80) and ES at presentation (HR=2.42, 95% CI 1.24–4.70) were independent predictors of arrhythmia recurrence. The independent predictors of all-cause mortality were ES (HR=2.17, 95% CI 1.33–3.54), LVEF (HR=0.95, 95% CI 0.92–0.98), age (HR=1.03, 95% CI 1.01–1.05), NYHA functional class III or IV (HR=2.04, 95% CI 1.12–3.73), and C-ABL (HR=0.22, 95% CI 0.05–0.91). The survival benefit was only seen in patients with a previous ablation (P for interaction=0.04) – Figure 1. Mortality at 30-days was similar between NC-ABL and C-ABL (4% vs. 2%, respectively, P=0.777), as was the complication rate (10.3% vs. 15.1% respectively, P=0.336). Conclusion A combined endo-epicardial approach appears to be associated with greater VT-free survival and overall survival in ischemic and nonischemic patients undergoing repeated VT catheter ablations. Both strategies seem equally safe. Survival analysis for C-ABL vs NC-ABL Funding Acknowledgement Type of funding source: None

Background Contemporary risk models to predict the recurrence of atrial fibrillation (AF) after pulmonary vein isolation have limited predictive ability. Models with high specificity seem particularly suited for the setting of AF ablation, where they could be used as gatekeepers to withhold intervention in patients with low likelihood of success. Machine learning (ML) has the potential to identify complex nonlinear patterns within datasets, improving the predictive power of models. This study sought to determine whether ML can be used to better identify patients who will relapse within one year of an AF ablation procedure. Methods We assessed 484 patients (294 men, mean age 61±12 years, 76% with paroxysmal AF) who underwent radiofrequency pulmonary vein isolation (PVI) for symptomatic drug-refractory AF. Using this dataset, a machine-learning model based on Support Vector Machines (SVM) was developed to predict AF recurrence within one year of the procedure. The following variables were used to feed the model: type of AF (paroxysmal vs. non-paroxysmal), previous ablation procedure, left atrium (LA) volume, and epicardial fat volume (both derived from pre-ablation cardiac CT). The algorithm was trained in a random sample of 70% of the study population (n=339) and tested in the remainder 30% (n=145). Results A total of 130 patients (27%) suffered AF recurrence within one year of the procedure. The ML model predicted AF recurrence with 75% accuracy (95% CI 67–82%), yielding a sensitivity and specificity of 25% (95% CI 13–41%) and 94% (95% CI 88–98%), respectively. The corresponding positive and negative predictive values were 62% (95% CI 39–81%) and 77% (95% CI 67–82%), respectively. The relative weight of the variables in the ML model was: epicardial fat 56%, type of AF 23%, previous ablation 14%, and LA volume 7%. A high-risk subgroup representing 10.8% of patients was identified with the ML algorithm. In this subgroup, one-year recurrence was 62%, representing 24% of the total number of recurrences. Conclusion A machine-learning model showed high specificity in the identification of patients who relapse during the first year after AF ablation. In the future, these tools may be useful to improve patient selection. Funding Acknowledgement Type of funding source: None

Introduction Direct comparisons of long-term clinical outcomes of endocardial vs. epicardial catheter ablation techniques for drug-resistant ventricular tachycardia (VT) have been scarcely reported. We aim to compare the long-term efficacy and safety of endocardial vs. epicardial catheter ablation (END-ABL and EPI-ABL, respectively) in a propensity score (PS) matched population. Methods Single-center observational registry including 215 consecutive patients who underwent END-ABL (181) or EPI-ABL (n=34) for drug-resistant VT between January 2007 and June 2018. Efficacy endpoint was defined as VT-free survival after catheter ablation, while safety outcomes were defined by 30-days mortality and procedure-related complications. A propensity score was used to match patients in a 1:1 fashion according to the following variables: VT storm at presentation, left ventricular ejection fraction (LVEF), New York Heart Association (NYHA) class III/IV at presentation, ischemic ethology, presence of implantable cardioverter-defibrillator (ICD), and previous endocardial catheter ablation. Independent predictors of VT recurrence were assessed by Cox regression. Results The PS yielded two groups of 31 patients each well matched for baseline characteristics (Table 1). Over a median follow-up of 2 years (IQR 1–3), 58% (n=18) ENDO-ABL patients had VT recurrence vs. 26% (n=8) in the EPI-ABL group (P=0.020). The yearly rates of VT recurrence were 28%/year for END-ABL vs. 11%/year for EPI-ABL (P=0.021). Multivariate survival analysis identified previous endocardial ablation (HR= 3.52; 95% CI 1.17–10.54, p=0.026) and VT storm at presentation (HR=3.57; 95% CI 1.50–8.50, p=0.004) as independent predictors of VT recurrence. EPI-ABL was independently associated with fewer VT recurrences (HR=0.28; 95 CI 0.12–0.69, p=0.005), but only in patients with a previous endocardial ablation (p for interaction = 0.004) – Figure A. No patients died at 30-days post-procedure. Hospital length of stay was similar between END-ABL and EPI-ABL (5 vs. 4 days respectively, p=0.139), as was the complication rate (6.5% vs. 12.9% respectively, p=0.390), although driven by different causes (Table 1). Conclusion VT storm at presentation and previous catheter ablation were independent predictors of VT recurrence. In patients with a previous failed endocardial catheter ablation, epicardial ablation seems to provide greater VT-free survival than repeat endocardial ablation. Both strategies seem equally safe.

Introduction Pulmonary vein (PV) reconnection is a common cause of relapse after catheter ablation of atrial fibrillation (AF). However, some patients have AF recurrence despite durable PV isolation. The aim of this study was to assess the PV isolation status at the time of a second catheter ablation (redo) procedure, and its relationship with subsequent AF relapse. Methods Consecutive patients with symptomatic drug-resistant AF who underwent redo procedures from January 2006 to December 2017 were identified in a single-center observational registry. Pulmonary vein isolation status was assessed during the electrophysiologic study with a circular mapping catheter. Additional radiofrequency (RF) energy applications were also recorded. AF relapse was defined as symptomatic or documented AF/atrial tachycardia/atrial flutter after a 3-month blanking period. Results We identified 240 patients (77 [32%] females, median age 61 [IQR 53–67] years, 85 [35%] with non-paroxysmal AF) undergoing redo procedures during the study period. At the time of redo, 17 (7%) of the patients presented bidirectional conduction block of all PVs. PV reconnection occurred in 157 (65%) of cases in the left superior vein, 142 (59%) in the left inferior vein, 177 (73%) in the right superior vein, and 163 (68%) in the right inferior vein (table). All of the PVs were reconducted in 91 (38%) patients. Additional RF applications were performed in the left atrium (LA) roof, LA posterior wall, cavotricuspid isthmus, mitral isthmus, superior vena cava, coronary sinus, and left atrial appendage ostium, at the operator's discretion (table 1). Over a median follow-up of 2-years (IQR 1–5), 126 patients (53%) suffered AF recurrence, yielding a mean relapse rate of 17%/year. In multivariate Cox regression analysis, the lack of PV reconnection at the time of redo emerged as an independent predictor of subsequent relapse (HR 1.97, 95% CI 1.12–3.49, p=0.019) even after adjustment for univariate predictors including non-paroxysmal AF, body mass index, female sex, and active smoking. Conclusion In patients undergoing redo AF ablation procedures, less than 10% present with complete PV isolation. Despite being relatively infrequent, this finding is independently associated with greater likelihood of subsequent recurrence, suggesting that other mechanisms, not fully addressed by additional RF applications, are at play.

Introduction Pericardial adipose tissue has been implicated in the pathophysiology of atrial fibrillation (AF), but its relevance to clinical practice remains uncertain. The aim of this study was to assess the relative importance of pericardial fat as predictor of recurrence after pulmonary vein isolation (PVI). Methods We assessed 453 patients (278 men, age 61±13 years, 348 paroxysmal AF) with symptomatic AF undergoing cardiac CT prior to a PVI procedure. Pericardial fat was quantified on contrast-enhanced images using a new simplified semi-automated method. The study endpoint was symptomatic and/or documented AF recurrence. Results Over a median follow-up of 14 months (IQR 7–23), 170 patients (38%) relapsed. Survival analysis showed significant differences in AF-free survival across tertiles of pericardial fat (Figure). Pericardial fat volume was weakly correlated to body mass index [(BMI), Pearson's R=0.34]. After adjustment for BMI and other univariate predictors of relapse, three variables emerged independently associated with time to AF recurrence: non-paroxysmal AF (HR 2.08, 95% CI: 1.51–2.87, p Conclusion Pericardial fat volume is a strong independent predictor of AF relapse after PVI, outperforming classic risk markers such as LA volume and type of AF. The underlying mechanisms of this association deserve further study. Meanwhile, this simple parameter may help select patients who are more likely to derive sustained benefit from AF ablation.