Posters 270Oversensing in subcutaneous implantable cardioverter-defibrillators71Early stimulation of the fast-conducting endocardium is the primary factor in reducing myocardial activation times for endocardial cardiac resynchronisation therap72The impact of age on outcomes in primary prevention icd recipients: a competing risks analysis73The effects of epicardial and endocardial pacing on the constituent waves of coronary flow: coronary resynchronisation74Manifestation of repolarisation and conduction abnormalities following exercise in concealed type 1 brugada75Delivering universal public access automated external defibrillators in the united kingdom: starting at the heart of the community76Under use of oral anticoagulation in new patients with atrial fibrillation: a clinical practice research datalink study77Complete extraction of abdominal pacing and icd leads- a unique case series78The impact of adjunctive complex fractionated atrial electrogram ablation and linear lesions on outcomes in persistent atrial fibrillation: a meta-analysis79Analysis of two novel risk calculators for the prediction of cardiac implantable electronic device infection80General anaesthesia improves the success rates of pulmonery vein isolation for paroxysmal atrial fibrillation ablation: Table 1

Background: Subcutaneous implantable cardioverter-defibrillators (S-ICDs) have been shown to be limited by relatively high incidence of oversensing of the cardiac signal compared to transvenous ICDs. The S-ICD only stores electrograms once a signal is sensed in the tachycardia zones and charging is initiated. Little is known about oversensed signal that does not result in shock therapy. Aim: To characterise and evaluate the incidence of oversensed signal amongst S-ICD recipients at two UK centres. Methods: S-ICD interrogation data was analysed from 130 S-ICD recipients implanted at Russells Hall Hospital, West Midlands and the University Hospital Southampton NHS Foundation Trust between February 2009 and May 2015. Results: Forty-five separate episodes of oversensed signal were recorded in 21 patients (16.2%). Noise was the most common cause of oversensing accounting for 26 (57.8%) of all episodes with 3 shocks being delivered. Twenty-one shocks were delivered to eleven patients (8.4%) during 18 episodes (1.2 shocks per episode). Three patients had more than one cause for the oversensed signal. Three patients received more than 1 shock. T-wave or P-wave oversensing during an atrial rhythm was associated with 84.6% risk of subsequent shock delivery and occurred in 8 (6.2%) of patients. The median time to oversensed event was 3.68 months. Oversensing episodes were managed according to cause. Measures included reprogramming vectors and shock zones, updating software, ablation of troublesome arrhythmias, identifying and correcting source of noise (electrical rewiring of home appliances) and adding/increasing anti-arrhythmic medication. In two individuals these interventions were unsuccessful and their S-ICD explanted. The remaining 19 individuals had a median oversensing free time since last episode of 30.0 months. <tbl id="EUV330TB1" loc="float"><no>Table 1</no> Causes and frequency of oversensed signal and the risk of subsequent shock delivery <tblbdy><r><c cspan="1" rspan="1"><f><inline-fig> <link locator="euv33001"></inline-fig></f></c></r></tblbdy></tbl> Conclusion: Oversensed signal is a relatively frequent occurrence in this S-ICD population, though only a minority of patients receive an ICD shock as a consequence. If oversensing occurs, it tends to occur relatively soon following S-ICD implantation. Noise is the most common cause of oversensed signal but rarely results in shock delivery. The majority of cases were successfully managed with a combination of programming changes, software ware improvements, treating electromagnetic interference and medication.