• Electrocardiography
• epidemiology

Most patients with myocardial infarction (MI) present with severe clinical symptoms such as angina pectoris. If the patient has no symptoms or atypical symptoms, the MI may be categorised as ‘silent’. In some (but not all) cases, silent MI may be later identified and referred to as ‘unrecognised MI’. Unrecognised MI is a common and clinically significant event. Data from several epidemiological studies that defined previous MI by the presence of abnormal Q waves on an electrocardiogram (ECG), suggest that 20– 40% of all MIs are unrecognised.1 An earlier publication of the Rotterdam Study reported an even higher proportion of 53% unrecognised MIs in older women.2 Importantly, an unrecognised Q-wave MI has significant clinical implications and carries a prognosis that is as poor as that for recognised MIs.3 4 In the Framingham Study, for example, 58% of men and 48% of women had died within 10 years after detection of unrecognised Q-wave MI: a rate similar to that seen in subjects with recognised MIs.3 In a more recent analysis of elderly subjects from the Cardiovascular Health Study, 7-year mortality was similar in those with clinically unrecognised and those with recognised MI (21% vs 25%, respectively).5

Most epidemiological studies investigating the relevance of ECG-based unrecognised MI have focused on mortality as outcome variable, with insufficient study of cardiovascular morbidity. Particularly, development of heart failure (HF) is an important predictor of long-term outcome after MI, and should therefore receive special attention in such studies.6 7 Even today, with enhanced treatment options for HF, this condition is still associated with severely reduced life expectancy, higher rates of hospitalisation and, not least, with significant reduction in quality of life.6 8 9 In a population-based setting, the impact of unrecognised MI on incident HF was investigated only …