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Funding Acknowledgements Type of funding sources: None. Background Pulmonary vein isolation (PVI) remains the cornerstone for treating of symptomatic atrial fibrillation (AF). Single-shot PVI technologies have evolved as a standard for first-time PVI. A novel radiofrequency balloon ablation catheter is now available to offer single-shot RF pulmonary vein isolation. Purpose To summarize the early experience using the novel RF balloon ablation catheter for patients undergoing PVI in two tertiary centres in Europe. Methods We prospectively assessed the first 38 consecutive patients undergoing PVI using RF balloon ablation catheter for paroxysmal or persistent AF in two high volume centres. Both centres used a standardised approach including ultrasound-guided vascular access, uninterrupted anticoagulation, transeptal puncture via the RF balloon sheath and a limited 3D mapping software-guided LA geometry created with a circular mapping catheter. Radiofrequency application for 60s to the anterior segments and 20s posteriorly was performed in all cases, phrenic pacing was employed for ablation of right PVs. BHS performed all procedures (except 2 cases due to high BMI and severe sleep apnea) under sedation, while all patients from UHZ underwent PVI procedures with general anaesthesia as per institutional protocol. All patients had an oesophageal temperature probe to assess oesophageal temperature during ablation (passed orally under sedation) and had uninterrupted oral anticoagulation throughout the periprocedural period. Results Overall, mean age was 64±8 years, 23 (61%) were male, 24 (63%) of patients had paroxysmal AF. The majority were de novo interventions (92%). There was no significant difference between the patients demographics in the two hospitals. All veins were isolated in both groups with a total of 144 applications (n = 73 in the sedation group, n = 71 in the GA population). Median fluoroscopy time was comparable (sedation group 1.1 minutes vs GA group 1.2 minutes; P = 0.58), but median procedure time was shorter in the sedation group (65 minute vs 106 minutes; P < 0.001). The median number of RF ablation per patient (sedation group 7 vs GA group 9; P = 0.32) and time to isolation of each vein (sedation group 11 seconds vs GA group 10 seconds; P = 0.9) were similar. Number of acute reconnections requiring further ablations were not significantly different between groups (sedation group 11 [15%] vs GA group 14 [20%]; P = 0.96). One patient sustained transient phrenic nerve injury in the sedation group. Conclusion Our early experience shows the novel HS balloon ablation can be performed effectively, efficiently and safely under either GA or conscious sedition. The RF balloon ablation catheter paradigm lends itself to refined workflows, with low fluoroscopy requirements and a short learning curve even in initial cohorts.

Background Maintenance of sinus rhythm is challenging in patients with longstanding persistent atrial fibrillation (PeAF). Minimally invasive surgical AF ablation may improve outcomes when combined with catheter ablation (the ‘convergent’ procedure). This study evaluates the safety and efficacy of the convergent procedure versus catheter ablation alone in longstanding PeAF. Methods 43 consecutive patients with longstanding PeAF underwent subxiphoid endoscopic ablation of the posterior left atrium followed by catheter ablation from 2013 to 2018. The primary outcome was AF-free survival at 12 months; secondary outcomes included change in EHRA class, echocardiographic data, procedural complications, freedom from anti-arrhythmic drugs (AADs), and long term arrhythmia-free survival. Outcomes were compared with a matched group of 43 patients who underwent catheter ablation alone. Both groups underwent multiple catheter ablations as required. Baseline characteristics were similar between groups. Results After 12 months, the convergent procedure was associated with increased AF-free survival on AADs (60.5% versus 25.6%, p = .002) and off AADs (37.2% versus 13.9%, p = .025), versus catheter ablation. Allowing for multiple procedures, after 30.5 ± 13.3 months' follow-up the convergent procedure was associated with increased arrhythmia-free survival on AADs (58.1% versus 30.2%, p = .016) and off AADs (32.5% versus 11.6%, p = .036) versus catheter ablation. There were more complications in the convergent procedure group (11.6% versus 2.3%, p = .2). Multivariate analysis identified only the convergent procedure (OR 3.06 (1.23–7.6), p = .017) as predictive of arrhythmia-free survival long term. Conclusions In longstanding PeAF, the convergent procedure is associated with improved arrhythmia-free survival versus catheter ablation alone. Complication rates are significant but have been shown to depreciate with experience.

Funding Acknowledgements Type of funding sources: Public Institution(s). Main funding source(s): British Heart Foundation Imperial Centre of Research Excellence Background/Introduction ECG algorithms for identifying accessory pathway (AP) locations are inaccurate and difficult to use. Human expert interpretation is poorly reproducible. Artificial intelligence (AI) techniques such as machine learning can improve accuracy in classification tasks by eschewing theory-driven predictions. More reproducible and accurate AP localisation could shorten procedure time and personalise ablation consent. Purpose We developed a neural network to perform AP localisation using 12-lead ECGs. Its decision-making process was analysed to enable explainability of the neural network. Methods A convolutional neural network was trained on raw, digital, intra-procedural 12-lead ECGs of patients with manifest APs who underwent successful ablation. ECGs were labelled with AP locations as left-sided, septal or right-sided using procedure reports, fluoroscopy and electro-anatomical maps. Accuracy of the neural network was assessed via 4-fold cross-validation and was compared to the Arruda algorithm. Five cardiologists were also assessed for their accuracy in determining locations in sub-groups of cases. The neural network was retrospectively analysed to identify areas of ECGs most influential to its predictions using importance mapping. Results In 156 cases, accuracy of the neural network (92.9%) was significantly higher than the Arruda algorithm (76.9%; p The figure shows (A) architecture of the neural network, (B) accuracy of the neural network, Arruda algorithm and five cardiologists, (*, p = 0.05 – 0.01; **, p = 0.01 – 0.001; ***, p = 0.001 - 0.0001; ****, p Conclusion AI ECG interpretation allows accurate, reproducible prediction of AP locations, superior to conventional algorithms and human interpretation. Although AI decision-making is thought of as a ‘black box’, explanation visualisation techniques such as importance mapping allow humans to understand aspects of how a neural network make decisions. A prospectively validated neural network could be integrated into clinical practice to improve pre-procedural AP localisation. Abstract Figure. Summary of results

In patients with longstanding persistent atrial fibrillation (AF), outcomes from catheter ablation remain suboptimal. The convergent procedure combines minimally invasive surgical ablation with subsequent catheter ablation, and may contribute towards maintenance of sinus rhythm in this patient group. We performed the convergent procedure on 43 patients with longstanding persistent AF from 2013-2018. Patients underwent clinical review at 3, 6, and 12 months and thereafter as necessitated by their symptoms. Our dataset describes patients' baseline characteristics and rhythm control protocols, as well as outcomes including arrhythmia recurrence, the need for antiarrhythmic drugs, requirement for repeat rhythm control procedures, and complications. These data provide a real world insight into the risks and benefits of the convergent procedure in patients with longstanding persistent AF.

Introduction Activation and entrainment mapping of VT remains the gold standard for identifying critical sites for ablation of VT, however, this method is limited by poorly tolerated or non-sustained VT. Several substrate guided approaches have been developed, however, outcomes when comparing both methods are similar and overall success can be as low as 47%. A key element in facilitating VT is the presence of dynamic changes within the substrate which may not be evident during sinus rhythm substrate mapping, but may form a critical aspect of the tachycardia mechanism when conduction velocity slows dynamically and tissue refractory periods lengthen. These are rarely studied as part of clinical VT mapping. Purpose This study aimed to investigate dynamic substrate changes to local abnormal ventricular activity (LAVA) and late potentials (LP), in relation to critical sites for VT ablation using high resolution mapping of the ventricle with the HD Grid (Abbott, Inc, USA), during short coupled singe extra stimuli from the right ventricle (RV) (Barts Sense Protocol), designed to invoke conduction delay. We hypothesized that the dynamic functional late potential mapping would improve the identification of critical substrate and ablation of these regions would improve outcomes. Methods Thirty patients (age 67 +/- 9yrs, 27Male) underwent ablation. Mean ejection fraction was 25% (+/- 10%). Mapping was performed with the AdvisorTM HD Grid multipolar catheter. A bipolar voltage map was obtained during sinus rhythm (SR) and RV Sensed Protocol (SP) single extra pacing. SR and SP late potential (LP) and local abnormal ventricular activity (LAVA) maps were made and compared with critical sites for ablation, defined as sites of best entrainment or pace mapping. Ablation was then performed to critical sites and LP/LAVA identified by the SP. Results At a median follow up of 10 months 90% of patients were free from symptomatic ATP or ICD shocks. The median area of late potentials across the 30 patients during sinus rhythm was 6.4mm2 during sinus rhythm mapping and 19.3mm2 during sense protocol pacing (p = 0.001). The functional unmasking of LP and LAVA was seen in 26 patients and showed good correlation to critical regions of the VT circuit (sites of best entrainment or pace map). In 24 patients functionally unmasked late potentials were located within 10mm of critical regions within the mapped VT circuit, with a median distance of 8.5mm, compared to 7 patients during sinus rhythm mapping with a median distance of 22mm (p= Conclusion Functional LP and LAVA can be unmasked by the sense protocol enabling better delineation of critical regions for VT ablation which may not be visible during sinus rhythm. This unique delineation of functional substrate changes combined with activation or pacemapping may improve outcomes. Abstract Figure 1

A. McLellan1,2,3, L. Ling1,2,3, S. Azzopardi 1,2, G. Lee1,2, G. Lee1,2,3, S. Kumar1,2,3, M. Wong1,2,3, T. Walters 1,2,3, J. Lee 3, K. Halloran3, M. Stiles 7, N. Lever 8, S. Fynn9, P. Heck9, P. Sanders 6, J. Morton3,4, J. Kalman3,4, P. Kistler 1,2,3,4,5,∗ 1 Alfred Heart Centre, Alfred Hospital, Melbourne, Victoria, Australia 2 Baker IDI Heart and Diabetes Institute, Melbourne, Victoria, Australia 3Department of Cardiology, Royal Melbourne Hospital, and Department of Medicine, University of Melbourne, Parkville, Victoria, Australia 4 Melbourne Private Hospital, Parkville, Victoria, Australia 5 Avenue Private Hospital, Windsor, Victoria, Australia 6 Centre for Heart Rhythm Disorders, University of Adelaide and Royal Adelaide Hospital, Adelaide, South Australia, Australia 7 Waikato Hospital, New Zealand 8 Auckland City Hospital, Auckland, New Zealand 9 Papworth Hospital, Cambridge, United Kingdom

Background: The last focused update of the ESC guidelines for the management of atrial fibrillation (AF) recommended to use antithrombotic therapy for the prevention of thromboembolic events for all patients with AF except in those at low risk. Nevertheless, little is known about the impact of these recommendations in clinical practice of different European countries. Methods: The PREvention oF thromboembolic events – European Registry in Atrial Fibrillation (PREFER in AF) recruited unselected patients in Austria, France, Germany, Italy, Spain, Switzerland and the United Kingdom from Jan 2012 to Jan 2013. We report the data collected at enrolment into the study. Results: 7243 consecutive patients were enrolled. 5856 of them had a transthoracic echocardiography performed in the 12 months period prior to inclusion. While the overall prevalence of patients with CHA2DS2-VASc of 0 was very low, there were 1282 (17.7%) patients who did not receive antithrombotic therapy, including 808 patients (11.2%) who received antiplatelet (AP) therapy and 474 patients (6.5%) who had no preventive treatment at all. Patients who received AP or no preventive treatment had a lower prevalence of left atrial dilation than the overall population of the study (59.0% and 48.3% respectively vs. 70.1%, p

Purpose: Electrogram attenuation has previously been utilised as marker of effective ablation. Contact force during ablation has recently been shown to be predictive of pulmonary vein reconnection. We sought to investigate the relationship between contact force during persistent atrial fibrillation (PeAF) ablation and electrogram attenuation. Methods: 15 patients undergoing ablation for PeAF were studied. Patients had electrograms recorded using LabSystem Pro before and 8 seconds after a 30 second ablation with the catheter kept in the same location. Contact force was recorded using a SmartTouch catheter and Carto 3The electrograms were analysed using custom Matlab scripts. Deflections of

Introduction Although atrial fibrillation (AF) has deleterious effects in patients with heart failure (HF), rhythm control using medication has limited efficacy. Catheter ablation (CA) of AF is effective in restoring sinus rhythm, raising the question: if it can be shown to be safe and effective in HF patients, might it improve left ventricular (LV) function and HF symptoms? We sought to compare the impact of a CA strategy to a medical rate control strategy (MED) in patients with persistent AF and HF. Methods Patients with persistent AF, symptomatic HF, and a LV ejection fraction (EF) Results 55 patients were randomised, but five were excluded (LV function normalised during optimisation of medications prior to baseline tests in 2, and 3 withdrew un-happy with their treatment allocation). Patients were 58±11 years and 96% were male. Baseline LV EF was 31±10% in the CA group and 33±9% in the MED group. NYHA class was 2.5±0.5 in both groups. Patients underwent 1.6±0.7 procedures. There were two complications: (1) stroke and 1 tamponade. In the CA group 1 patient withdrew after a procedural stroke, and in the MED group 1 patient died. In total 21 of 24 in the MED group and 24 of 26 in the CA group had reached 6-months follow-up and were included in this analysis of the primary end-point. Freedom from AF was achieved in 21/24 (88%) off antiarrhythmic drugs in the CA group, whereas all those in the MED group remained in AF. LV EF in the CA group at 6 months was 39±10% compared to 32±13% in the MED group (p Conclusions CA is effective in restoring sinus rhythm in the majority of patients with persistent AF. A CA strategy for patients with AF and HF is associated with improved LV function and heart failure symptoms compared to medical treatment alone.

Introduction Reports of the prevalence of left atrial appendage (LAA) thrombus among patients undergoing catheter ablation for atrial fibrillation (AF) vary and may depend on the anticoagulation regime used prior to the procedure. Methods We undertook transoesophageal echocardiograms (TOE) in 586 patients (age 59.9±0.4 years old, mean±SE, 64.5% male) undergoing catheter ablation for AF who were anti-coagulated on warfarin (international normalised ratio 2–3) for at least 3 consecutive weeks prior to procedure and maintained on warfarin for the procedure itself. Results LAA thrombus was identified in 3 patients from 586 (0.5%) despite all 3 having therapeutic INRs (2.2, 2.2 and 3.3 respectively). None of the remaining patients had a peri-procedural stroke. The three patients with LAA thrombus had CHADS 2 scores of ≥1 and CHA2DS2-VASc scores of ≥2. All three patients had impaired left ventricular systolic function (LVSF), and LAA emptying velocities of 2 (0.9±0.1 vs 0.7±0.001) and CHA2DS2-VASc scores (1.7±0.1 vs 1.4±0.1), and larger LA diameter (4.95±0.09 vs 4.38±0.05 cm, OR for LA >4.6 cm: 2.4, 95% CI 2.13 to 5.41), and were more likely to have impaired LVSF (OR: 2.66, 95% CI 1.52 to 4.66) compared to those with higher velocities on multivariate analysis. Conclusions The prevalence of LAA thrombus using our anticoagulation regime is extremely low. Providing patients have been therapeutically anti-coagulated, pre-operative TOE need only be performed in patients with a CHADS 2 score of ≥1/CHA2DS2-VASc score of ≥2 or when LA diameter is >4.6 cm. This criteria has the highest sensitivity (84%) for identifying LAA velocities of

Introduction Implantable cardioverter defibrillators (ICDs) have been shown to reduce mortality in patients with ischaemic cardiomyopathy at a high risk of ventricular arrhythmias (VA), which are the commonest cause of sudden death. However, ICDs are associated with morbidity and mortality Importantly 67% of patients never receive an appropriate shock after ICD implantation under the current indication, suggesting a need for better risk stratification tools. Telomere and telomerase in leucocytes have recently been shown to correlate with biological aging, health status, and also with pathogenesis/prognosis of various cardiovascular diseases. We hypothesise that the leucocyte telomere length and/or telomerase activity correlate with the incidence of VA in ischaemic cardiomyopathy patients. Methods 73 ischaemic cardiomyopathy Caucasian patients with primary prevention ICDs were recruited to this retrospective study between October 2010 and January 2011 at St Bartholomew9s Hospital. Concentrated leucocyte fraction was obtained from venous blood sample of recruited patients and stored at −80°C in an anonymous manner. Genomic DNA was extracted from these and telomere length measured by telomere PCR. Each telomere length was expressed as a ratio (telomere length: single copy gene). Telomerase activity was measured using Roche Telo TAAGGG ELISA kit. All samples were analysed in duplicate and investigators were semi-blinded to arrhythmia history. Continuous data were compared using unpaired t test and categorical data by χ 2 test. Logistic regression analysis was performed to determine if telomere length/telomerase activity independently predict the likelihood of a shock (fatal VA). A probability value of p Results There were no significant differences between the Shock (patients received appropriate shocks from ICD; n=25) and Non-shock (patients received no shock; n=48) groups in terms of baseline demographics as shown in Abstract 056 table 1. There was no significant difference in the age, sex and WCC adjusted telomere length between the Shock and Non-shock groups (p=0.439). Expected age and WCC turnover related telomere attrition (p=0.031 and 0.031) was observed. In contrast, telomerase activity was significantly higher in the Shock group thank in the Non-shock group (0.5682 vs 0.2105) and co-related to the incidence of shock (p=0.01). This did not appear to be related to an acute response associated with VA. Conclusion This is the first study to characterise the telomere dynamics of patients at high risk of sudden cardiac death and co-relate this with the incidence of VA. Leucocyte telomerase activity independently predicted the likelihood of shock in ischaemic cardiomyopathy patients with primary prevention ICDs. Thus leucocyte telomerase activity may be a potential biomarker for prediction of fatal arrhythmia and guide ICD prescription. To validate these results, a prospective study is now ongoing.

Introduction Targeting complex fractionated atrial electrograms (CFAE) in the ablation of atrial fibrillation (AF) may improve outcomes, although whether this is by eliminating focal drivers or simply de-bulking atrial tissue is unclear. It is also uncertain what electrogram morphology should be ablated. This randomised study aimed to determine the impact of ablating different CFAE morphologies compared to normal electrograms (ie, de-bulking normal tissue) on the cycle length of persistent AF (AFCL). Methods After pulmonary vein isolation CFAE were targeted systematically throughout the left then right atrium, until termination of AF or abolition of CFAE prior to DC cardioversion. 10 s electrograms were classified by visual inspection according to a validated scale, with Grade 1 being most fractionated and grade 5 normal. Patients were randomised to have CFAE grades eliminated sequentially, from grade 1 to 5 (group 1) or grade 5 to 1 (group 2). Because grade 5 electrograms were considered normal, only 5 were ablated. Mean AFCL was determined manually over 30 cycles from bipolar electrograms recorded at the left and right atrial appendages before and after each CFAE was targeted. Lesions were regarded as individual observations, and a resultant increase in mean AFCL ≥5 ms was regarded as significant. The randomised strategy first controlled for any cumulative effect of ablation on AFCL, and second allowed assessment of the order of ablation on the number of CFAE lesions required. Results 20 patients were randomised. The CFAE grade determined by rapid visual inspection for the 968 electrograms targeted agreed with that at off-line manual measurement in 92.7% (к=0.91). AFCL increased after targeting 49.5% of grade 1 CFAE, 33.6% of grade 2, 12.8% of grade 3, 33.0% of grade 4, and 8.2% of grade 5 CFAE (p Conclusion Targeting CFAE is not simply atrial de-bulking. Ablating certain grades of CFAE caused AFCL prolongation, suggesting they are more important in maintaining AF. Targeting these CFAE may reduce unnecessary left atrial destruction. (ClinicalTrials.gov number, NCT00894400).

Introduction We hypothesised that electrical isolation of the pulmonary veins (PV) by wide area circumferential ablation with radiofrequency (RFA) followed by selective PV ostial ablation using a cryoablation balloon (Cryo) would create parallel lines of block and reduce the incidence of PV reconnection.This would therefore improve first time success rates for paroxysmal atrial fibrillation (PAF). Methods A retrospective study examined 59 consecutive patients undergoing first time PV isolation for symptomatic PAF(>1 year) and had failed at least two medical therapies. Patients received RFA alone, Cryo alone or combined RFA (to isolate PVs) followed by Cryo. Patients were followed up with 12 lead ECG, 7 day Holter monitoring and clinical review. Any atrial arrhythmia lasting greater than 30 s during a 3 month follow-up period was documented as a recurrence. Results Significantly fewer patients had symptomatic palpitations (with documented PAF) in the combined group, with a trend towards need for less redo procedures (Abstract 135 table 1). Complications were one phrenic nerve palsy and one haematoma in the Cryo group, one grounding plate burn in the RF group and one phrenic nerve palsy , one pericardial effusion and one haematoma in the combined group. Total procedure time was greater in the combined group (Abstract 135 table 1). Conclusion Preliminary results suggest that combination of RF and Cryoablation is superior to either alone. A prospective randomised trial is underway to confirm these findings.