guidelines for primary prevention and, among the latter, what the underlying cardiac diagnoses were. Methods In a 5-year single-centre retrospective study within a large teaching hospital, we used the hospital electronic patient record to identify patients admitted with new presentation of ventricular arrhythmia, who did not have an ICD in-situ. Case-notes were reviewed to identify whether patients already had a known indication for ICD implant and to determine the cardiac background. Results Of 779 inpatient admissions with a code for ventricular arrhythmia, 302 patients were found to have had lifethreatening arrhythmia. Of these, 79 had already received ICD implant. The clinical status of the remaining 223 patients is shown in Table 1. After excluding patients with acute provocation (68) and 21 patients with severe LV impairment deemed ineligible for ICD therapy, 128 surviving patients were considered eligible to receive ICD implantation. Among these, 23 patients (18%) had a previously known guidelinebased indication for primary prevention ICD treatment, of whom 10 died without leaving hospital (43.5%). 53 patients (41%) had structural heart disease not meeting criteria for primary prevention ICD (Table 2). Conclusions Nearly one fifth of patients presenting to hospital with life-threatening ventricular arrhythmia and eligible for ICD therapy already had an identified indication for primary prevention ICD that had gone unrecognised, leading to potentially avoidable deaths. Two fifths of patients had cardiac disease falling outside of primary prevention guideline criteria. More widespread understanding of guidelines for recommending ICD therapy is important for ensuring that this treatment is offered to all eligible patients. This study suggests that current guidelines are unsatisfactory in identifying a substantial proportion of patients who may benefit from primary prevention ICD implantation.

Funding Acknowledgements Type of funding sources: None. Introduction Cardiac conduction disease and sudden cardiac death is known to be associated with Myotonic Dystrophy type 1 (MD). Patients often require device implantation to prevent sudden cardiac death. It is not known how frequently device implantation occurs and how quickly conduction disease progresses. Objective To define the rate and type of device implantation, rate of pacing and outcome in MD patients managed in a single specialist centre. Method Retrospective analysis of pacing and outcome data on consecutive MD patients managed at Specialist Centre in the UK between 2011 and 2021. Results 24/119 MD patients were implanted with a cardiac device. Male:Female 13:11. At implant, patients had a mean age of 56 (95% CI 52 to 59), mean PR interval 217 ms (95% CI 203 to 230), mean QRSd 123ms (95% CI 109 to 137). Devices implanted included 16 DDDR, 4 CRT-D, 1 CRT-P, 1- ICD and 2 VVI pacemakers. 10 (42%) died during follow up of 10 years. 12 out of 19 (63%) with an atrial pacing lead required a mean increase in atrial pacing of 15% (95% CI 5 to 25) during follow up. 12 out of 24 (50%) of patients required mean increase of 13% (95% CI 5 to 22) in Ventricular pacing. 7 (88%) patients who died had evidence of progressive conduction disease prior to death. Conclusion In our cohort of myotonic dystrophy patients 20% required device implantation. There was a higher incidence of progressive atrial rather than ventricular pacing, despite the known concern about progressive AV block. Despite pacing, mortality remained high and was more frequent in patients with progressive conduction disease. Increases in pacing demand could be early indicator of disease progression.

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