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The most common long-term complication of permanent pacemaker implantation is pacing-associated cardiomyopathy (PCM). PCM is present in as many as a third of patients with pacemakers implanted for bradycardia, is associated with lower quality of life, increased hospitalisation risk, and a worse prognosis. Although the likelihood of PCM is higher in those with a high burden of right ventricular pacing and cardiovascular co-morbidities, its occurrence is highly variable even amongst those with established cardiovascular disease. Approaches to prevent PCM, including upfront septal or biventricular pacing strategies, have resulted in neutral outcomes with increased costs and higher risk of complications. Hence, whilst data supporting the routine use of conduction system pacing are available, the default pacing strategy in most healthcare systems continues to be standard right ventricular pacing.Echocardiographic screening of populations with pacemakers identifies PCM in more than one third of patients. The initiation of medical therapies for heart failure or the provision of device upgrades to biventricular implantable cardioverter-defibrillators are two complementary strategies proven to improve clinical outcomes. However, the requirement for cardiac imaging to identify PCM is a significant workload challenge for most healthcare systems and may not be feasible unless screening is targeted to those at greater risk. Plasma concentrations of natriuretic peptides are recommended as an initial diagnostic test for ambulatory patients with signs and symptoms of heart failure (HF), and are almost universally elevated in its presence, whilst low concentrations reliably rule-out HF. Venous blood sampling or point-of-care natriuretic peptides assays might facilitate screening for PCM and potentially allow for more targeted cardiac imaging screening. However, conventional thresholds for natriuretic peptides have been derived from ambulatory populations in community-based settings, whilst the presence of right ventricular pacing or other cardiovascular co-morbidities which are common amongst this population might reduce their utility.Aims Pacing-associated cardiomyopathy (PCM) is the commonest long-term complication of permanent pacemaker implantation. In this analysis, we aimed to: describe the distribution of N-terminal pro-B-type natriuretic peptide (NT-proBNP) in a pacemaker population and its association with clinical characteristics, assess the ability of NT-proBNP to identify the presence of PCM (LVEF <50%), and explore the association between NT-proBNP and adverse clinical outcomes in patients with pacemakers.Methods and Results We conducted an analysis of the OPT-PACE (OPTimising PACEmaker therapy) – a multicentre, open-label, randomised controlled trial comparing echocardiographic screening of PCM with usual care. Following exclusion of 132 participants without baseline measurement of NT-proBNP, our final dataset comprised 1,069 participants, all of whom had complete follow-up data for the composite primary endpoint and its individual components.The median NT-proBNP was 406 pg/ml (range 10 to 30,854 pg/ml), and a total of 829 (77.5%) participants had a NT-proBNP of ≥ 120 pg/ml. 532 participants had echocardiographic data and 537 did not. Participants with PCM were more often male (70.2% vs. 29.8%, p<0.05), and were more likely to have ischaemic heart disease (23.6% vs. 14.7%, p<0.05) and type 2 diabetes mellitus (20.3% vs. 16.1%, p<0.05). They had, on average, a greater burden of atrial fibrillation (37.9% ± 47.2 vs. 20.7% ± 42.3, p<0.05) and a greater right ventricular pacing burden (58.4% ± 43.2 vs. 32.5% ± 39.9, p<0.05). There was a weak negative relationship between NT-proBNP and left ventricular ejection fraction (LVEF) (r=-0.37 [-0.44 to -0.30], R2=0.14) (figure 1). Using a NT-proBNP cut-off of ≥120 pg/ml, the sensitivity for detecting PCM was 0.86 (95% CI 0.80-0.91), specificity 0.26 (0.21-0.31), NPV 0.78 (0.71-0.85), and PPV 0.37 (0.35-0.39).Participants with NT-proBNP ≥1,000 pg/ml were 14.95 times (10.42-21.45) more likely to experience the primary composite outcome when compared with <120 pg/ml (figure 2). Participants with PCM were more often male (70.2% vs. 29.8%, p<0.05), and were more likely to have ischaemic heart disease (23.6% vs. 14.7%, p<0.05) and type 2 diabetes mellitus (20.3% vs. 16.1%, p<0.05). They had, on average, a greater burden of atrial fibrillation (37.9% ± 47.2 vs. 20.7% ± 42.3, p<0.05) and a greater right ventricular pacing burden (58.4% ± 43.2 vs. 32.5% ± 39.9, p<0.05)Conclusions In this analysis of the OPT-PACE randomised controlled trial we found natriuretic peptides were frequently elevated in patients with pacemakers, and that their diagnostic accuracy for detecting PCM was poor. Despite this, there was a strong correlation between NT-proBNP and the risk of adverse clinical outcomes.Abstract 47 Figure 1Scatter plot displaying the relationship between NT-proBNP and LVEFAbstract 47 Figure 2Kaplan-Meier curves demonstrating a) freedom from primary outcome; b) freedom from hospitalisation for heart failure; c) survival in patients with NT-proBNP <120 pg/ml, 120 – 399 pg/ml, 400 – 999 pg/ml, and ≥1,000 pg/ml