AbstractObjectiveTo evaluate the prognosis of unrecognised myocardial infarction determined by electrocardiography (UMI-ECG) or cardiac magnetic resonance imaging (UMI-CMR).DesignSystematic review and meta-analysis of prospective studies.Data sourcesElectronic databases, including PubMed, Embase, and Google Scholar.Study selectionProspective cohort studies were included if they reported adjusted relative risks, odds ratios, or hazard ratios and 95% confidence intervals for all cause mortality or cardiovascular outcomes in participants with unrecognised myocardial infarction compared with those without myocardial infarction.Data extraction and synthesisThe primary outcomes were composite major adverse cardiac events, all cause mortality, and cardiovascular mortality associated with UMI-ECG and UMI-CMR. The secondary outcomes were the risks of recurrent coronary heart disease or myocardial infarction, stroke, heart failure, and atrial fibrillation. Pooled hazard ratios and 95% confidence intervals were reported. The heterogeneity of outcomes was compared in clinically recognised and unrecognised myocardial infarction.ResultsThe meta-analysis included 30 studies with 253 425 participants and 1 621 920 person years of follow-up. UMI-ECG was associated with increased risks of all cause mortality (hazard ratio 1.50, 95% confidence interval 1.30 to 1.73), cardiovascular mortality (2.33, 1.66 to 3.27), and major adverse cardiac events (1.61, 1.38 to 1.89) compared with the absence of myocardial infarction. UMI-CMR was also associated with increased risks of all cause mortality (3.21, 1.43 to 7.23), cardiovascular mortality (10.79, 4.09 to 28.42), and major adverse cardiac events (3.23, 2.10 to 4.95). No major heterogeneity was observed for any primary outcomes between recognised myocardial infarction and UMI-ECG or UMI-CMR. The absolute risk differences were 7.50 (95% confidence interval 4.50 to 10.95) per 1000 person years for all cause mortality, 11.04 (5.48 to 18.84) for cardiovascular mortality, and 27.45 (17.1 to 40.05) for major adverse cardiac events in participants with UMI-ECG compared with those without myocardial infarction. The corresponding data for UMI-CMR were 32.49 (6.32 to 91.58), 37.2 (11.7 to 104.20), and 51.96 (25.63 to 92.04), respectively.ConclusionsUMI-ECG or UMI-CMR is associated with an adverse long term prognosis similar to that of recognised myocardial infarction. Screening for unrecognised myocardial infarction could be useful for risk stratification among patients with a high risk of cardiovascular disease.