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OBJECTIVES Atrial fibrillation (AF) is common and can cause significant morbidity and detriment to quality of life. Success rates for conventional catheter ablation are suboptimal in persistent AF (PsAF), especially when longstanding. Convergent hybrid ablation combines endoscopic surgical epicardial and endocardial catheter ablation. It offers promise in treating PsAF. We aimed to evaluate outcomes at our centre following convergent ablation. METHODS We conducted an observational study of patients undergoing ablation from 2012 to 2019 at a London cardiac centre. Sixty-seven patients underwent convergent ablation entailing epicardial ablation, mostly via sub-xiphoid access, followed by endocardial left atrial catheter ablation. Baseline and follow-up data were obtained retrospectively from clinical records. Primary outcome was freedom from AF on/off anti-arrhythmic drugs after 12-month follow-up. Secondary outcomes included freedom from AF over the entire follow-up, freedom from anti-arrhythmic drugs, freedom from atrial arrhythmias, symptom status, repeat ablation and complications. RESULTS At baseline, 80.6% had PsAF >1 year (80.6%), 49.3% had body mass index >30 kg/m2 at baseline and 19.4% had left ventricular ejection fraction of 40% or less. The median follow-up was 2.3 (1.4–3.7) years. Freedom from AF recurrence was 81.3% at 1 year and 61.5% over overall follow-up. Eleven patients (16.4%) required redo AF ablation. Prolonged AF duration was associated with increased recurrence at 12 months and duration >5 years with a shorter time to recurrence on Kaplan–Meier analysis, but this and other factors did not significantly impact the AF recurrence during the overall follow-up period. CONCLUSIONS Convergent ablation had good 1-year and overall success rates for treating PsAF. Our results in a diverse, real-world population support the potential of convergent ablation in patients with challenging to treat PsAF.

Funding Acknowledgements Type of funding sources: None. Background Relative benefits of transvenous lead extraction (TLE) should be weighed against the risks on an individual basis. Observational studies have identified disparate risk factors for major adverse events (MAEs), however there are few available tools to aid the clinician risk-stratifying patients. Purpose The purpose of this study was to develop a machine learning (ML)-based risk stratification system to predict risk of MAEs following transvenous lead extraction (TLE). Methods Multiple ML models were derived from a training cohort of 3555 patients undergoing TLE to pre-procedurally identify patients at high and low risk of major adverse events (procedure-related major complication, including procedure-related death). The ML models were then tested on an independent, reference centre cohort of 1171 patients undergoing TLE. Clinical features were selected based on whether they were available in both datasets without large gaps. For model selection we compared the ML algorithms logistic regression, ridge regression, support vector machines (SVM), gradient boosting classifier and random forest. The best performing of these was then compared to a self-normalising network (SNN). Results In total 3122 cases with the required features were included from the training cohort with 53 MAEs (1.7%), and 998 cases in the test cohort with 24 MAEs (2.4%). SVM identified lead dwell time, left ventricular ejection fraction (LVEF), estimated glomerular filtration rate (eGFR), chronic respiratory disease, local infection, heart failure, sepsis and male gender as predictors of MAEs in order of decreasing importance (see figure). For the training data, the SVM provided a more sensitive result compared with SNN (0.83 vs 0.71) at the cost of specificity (0.63 vs 0.79). For the test data, the SVM identified MAEs in 12 out of 123 (9.8%) "high risk" patients, 10 out of 552 (1.8%) "medium risk" patients, and 2 out of 323 (0.006%) "low risk" patients. Conclusion Machine learning provided good discriminative capabilities for identifying patients in a "high risk" and "low risk" category for MAEs. Abstract Figure. 8 most important predictors of MAEs

Funding Acknowledgements Type of funding sources: Private company. Main funding source(s): Medtronic Background / Introduction Endocardial pacing and conduction system pacing are emerging as alternative methods to deliver cardiac resynchronization therapy (CRT) and have been shown to achieve superior acute hemodynamic response (AHR) compared to conventional epicardial pacing. However, a direct comparison of all the methods of delivering CRT has not yet been performed. Purpose To directly compare the AHR of conventional CRT (BiV Epi), endocardial pacing (BiV Endo), His bundle pacing (HBP) and left bundle branch pacing (LBBP) during a temporary CRT study. Methods 4 patients underwent a temporary CRT and hemodynamic study. Temporary pacing was achieved using quadripolar catheters in the right atrium and coronary sinus, and roving decapolar catheters in the right ventricle (RV) and left ventricle (LV) via retrograde aortic access. Hemodynamic assessment was performed with a PressureWire X (Abbott, CA, USA) in the LV cavity. AHR was calculated as the percentage improvement in LV dP/dtmax from baseline AAI or RV pacing (if underlying complete heart block). Results The patients had a mean age of 67.5 ±5.8 years and all had non-ischemic cardiomyopathy with severe LV impairment (mean ejection fraction 22.5 ±7.4%). 3 patients had left bundle branch block and 1 patient had complete heart block with an RV paced rhythm (mean QRS duration 157 ±24 ms). All methods of delivering CRT achieved a mean AHR of >10%, which is considered clinically significant and is predictive of LV remodelling at 6 months. Mean AHR during BiV Epi pacing was 12.6 ±5.0%. There was a trend towards higher AHR for BiV Endo pacing (23.6 ±7.6%), HBP (17.4 ± 9.5%) and LBBP (16.1 ±7.8%) as shown in figure 1, however there was no significant difference between groups on one-way analysis of variance (p = 0.348). Conclusions All methods of delivering CRT achieved an AHR >10%. The AHR during BiV Endo pacing, HBP and LBBP was higher than for BiV Epi pacing, but this did not reach statistical significance. Further investigation with larger studies is required to determine which method of delivering CRT achieves the best hemodynamic response. Figure 1. Box plot of acute hemodynamic response (AHR) for conventional cardiac resynchronization therapy (BiV Epi), endocardial pacing (BiV Endo), His bundle pacing (HBP) and left bundle branch pacing (LBBP). Data displayed as median (solid line), mean (+), 1st and 3rd quartiles (box) and minimum and maximum values (whiskers). Abstract Figure 1

Funding Acknowledgements Type of funding sources: None. Background/Introduction: The significant rise in cardiac implantable electronic devices (CIED) has been paralleled by an increase in the number of procedures required for the removal of such devices and their associated leads. High procedural success rates with low rates of major in hospital complications is well recognised. Longer term mortality following transvenous lead extraction (TLE) is less well characterised. Long term outcomes are important as they should inform the decision making and consent process, especially in non-infected cases where there may not be a class I indication for lead removal. Purpose The purpose of this study was to evaluate the factors influencing survival in patients undergoing TLE depending on extraction indication. Methods Clinical data from consecutive patients undergoing TLE in the reference centre between the years 2000 to 2019 were prospectively collected. Only patients surviving to discharge were included. The total cohort was divided into groups depending on whether there was an infective or non-infective indication for TLE. We evaluated the association of demographic, clinical, device related and procedure-related factors on mortality. Results A total of 1151 patients were included in the analysis. 632 (54.9%) and 519 patients (45.1%) were for infective and non-infective indications respectively. Analysis of long-term outcomes on the total cohort (mean 66-month follow-up) revealed a mortality of 34.1% (392 deaths). A higher proportion of patients died in the infection vs the non-infection group (38.6% vs 28.5%, p Conclusion Long-term mortality for patients undergoing TLE remains high. Consensus guidelines recommend evaluating risk for major complications when determining whether to proceed with TLE. This study suggests assessing longer-term outcomes when considering TLE, particularly for non-infective indications. Abstract Figure.

Funding Acknowledgements Type of funding sources: None. Background Among patients undergoing transvenous lead extraction (TLE), differences in complication rate and 1-year mortality has been explored in patients with cardiac resynchronisation therapy (CRT) devices. Longer term outcomes and the influence of timing of reimplantation of device, with respect to rehospitalisation and longer-term mortality is poorly understood. Purpose The purpose of this study was to evaluate whether early reimplantation following TLE in patients with CRT devices influenced survival and rehospitalisation. Methods Clinical data from consecutive patients undergoing TLE in the reference centre between the years 2000 to 2019 were prospectively collected. Patients surviving to discharge who were re-implanted with the same device were included. The cohort was split depending on whether or not they had a CRT device at time of explant. The association between TLE in CRT patients and all-cause mortality and re-hospitalisation was assessed by Kaplan Meier estimates in a 1:1 propensity-score matched cohort, with a calliper of 0.10. Early reimplantation was defined as reimplantation within 7 days of TLE, and late reimplantation as reimplantation after greater than 7 days of TLE. Results Of 1005 patients included in the analysis, 285 (25%) had a CRT device. After matching, 192 CRT patients were compared with 192 non-CRT patients. Propensity scores were calculated using 39 baseline characteristics, including age, gender, co-morbidities, TLE indication, left ventricular ejection fraction, baseline creatinine and technical extraction data. Mean follow up was 53.5 ± 38.3 months, mean age at explant was 67.7 ± 12.1 years, 83.3% were male and 54.4% had an infective indication for TLE. In the matched cohort, there was no significant difference between the CRT and non-CRT group with respect to long-term mortality (hazard ratio [HR] = 1.01, 95% confidence interval [CI] [0.74-1.39], p = 0.093) or rehospitalisation (HR = 1.2 [0.87-1.66], p = 0.265). A similar proportion of patients were reimplanted within 7 days in the CRT and non-CRT groups (59.4% vs 61.5%, p = 0.754). In the matched non-CRT group, late reimplantation was associated with similar mortality to early reimplantation (HR = 1.33 [0.86-2.05], p = 0.208) and rehospitalisation (HR = 0.88 [0.53-1.45], p = 0.603). In the matched CRT group, late reimplantation was associated with higher mortality (HR = 1.64 [1.04-2.57], p = 0.032) and rehospitalisation (HR = 1.57 [1.00-2.46], p = 0.049] (see figure). Conclusion In this closely matched population, TLE in CRT patients resulted in similar long-term outcomes compared with non-CRT patients. Early reimplantation post CRT explant was associated with reduced long-term mortality and rehospitalisation. This suggests a longer duration without biventricular pacing post TLE may induce negative reverse-remodelling and should be avoided in a CRT population. Abstract Figure. Kaplan-Meier survival curves

Funding Acknowledgements WT 203148/Z/16/Z; MR/N011007/1; RE/08/003; PG/15/91/31812; PG/16/81/32441 Background Endocardial pacing has been shown to improve response to cardiac resynchronization therapy (CRT) in comparison to conventional epicardial pacing and the physiological activation, endocardium to epicardium, is proposed to make it less arrhythmogenic. However, the relative arrhythmic risk of endocardial and epicardial pacing has not been systematically investigated. Pacing in proximity to scar increases susceptibility to arrhythmogenesis during epicardial pacing. Whether this is also the case during endocardial pacing is currently unknown. Purpose We investigate 1) whether endocardial pacing is less arrhythmogenic than epicardial pacing, 2) whether pacing location relative to scar plays a role in arrhythmogenesis during endocardial pacing, and 3) whether these findings could be explained by the direction of the transmural action potential duration (APD) gradient. Methods We used computational models of ischemic heart failure and patient-specific (n = 24) left ventricular anatomy and scar morphology to simulate repolarization during endocardial and epicardial pacing. Pacing locations were selected 0.2-3.5cm from a scar. We ran simulations with a 20ms transmural APD gradient, as found in heart failure, from the epicardium to endocardium (physiological) and with this gradient inverted. We computed the volume of high (>3ms/mm) repolarization gradients (HRG) within 1cm around a scar, as a surrogate for arrhythmia risk, and analysed these with ANOVA and Tukey-Kramer post-hoc tests. Results Simulations with a physiological APD gradient predict that endocardial pacing creates a smaller (34%) volume of HRG around (1cm) a scar compared to epicardial pacing when pacing 0.2cm from scar (Figure 1-A). The volume of HRG decreases (P from scar for epicardial pacing but not endocardial pacing (Figure 1-A). Inverting the transmural APD gradient, inverts the trend observed with a physiological gradient. In this case, the volume of HRG is unaffected by pacing location during epicardial pacing, whereas it decreases (19%) with the distance from scar for endocardial pacing. This is illustrated in the regions highlighted in yellow in Figure 1 for endocardial pacing at 0.2 and 3.5cm from a scar with a physiological (B) and an inverted (C) gradient. Conclusions Endocardial pacing is less arrhythmogenic (purpose 1) than conventional epicardial pacing when pacing in proximity to scar and is also less susceptible to pacing location relative to scar (purpose 2). The direction of the transmural APD gradient offers a mechanistic explanation for reduced susceptibility to arrhythmogenesis during endocardial pacing compared to epicardial pacing (purpose 3). Endocardial pacing is an attractive alternative to conventional epicardial pacing in patients with scar, as it allows pacing in proximity to scar while avoiding increasing arrhythmogenic risk in patients with ischemic heart failure. Abstract Figure.