The risk of myocardial infarction in patients with atrial fibrillation: an unresolved issue

Abstract

Atrial fibrillation (AF) is the most common sustained dysrhythmia encountered in clinical practice in North America and Europe, accounting for approximately onethird of all hospitalizations for a cardiac rhythm abnormality [1]. The presence of AF markedly increases the patient’s risk for developing arterial embolism and stroke, depending on the presence of other clinical conditions, such as hypertension and diabetes [2]. AF is associated with a fivefold increased risk for stroke, and is estimated to cause 15% of all strokes. The rate of ischemic stroke among patients with non-valvular AF averages 5% per year, 2–7 times that of people without AF. Additionally, when transient ischemic attacks (TIAs) and clinically ‘‘silent’’ strokes are considered, the rate of brain ischemia accompanying non-valvular AF exceeds 7% per year. Patients with AF frequently have several risk factors for atherosclerosis, including hypertension, diabetes, and dyslipidemia [3, 4]. Accordingly, systemic signs of atherosclerosis can be detected in AF patients, and these likely account for an enhanced risk of coronary heart disease (CHD). In addition to cerebrovascular disease, patients with AF may suffer from coronary events including myocardial infarction (MI), but the rate of MI in AF patients seems to be variable, but often underestimated. Surprisingly few studies with antithrombotic drug therapy include MI as an end-point. We reasoned that analysis of the MI rate in AF could be useful for future interventional trials with anti-thrombotic drugs. Thus, we evaluated the rate of MI in the clinical trials where this clinical end-point was taken into account, and tried to relate it with the common atherosclerotic risk factors. Searches were conducted in computerized publication database (Medline) with hand searches of publications from January 1995 to September 2008. Bibliographies of all selected articles and review articles were reviewed for other relevant articles. We used search terms including ‘‘atrial fibrillation’’ and ‘‘cardiovascular risk’’, ‘‘atrial fibrillation’’ and ‘‘myocardial infarction’’, ‘‘atrial fibrillation’’ and ‘‘coronary heart disease’’, ‘‘atrial fibrillation’’ and ‘‘mortality’’, ‘‘atrial fibrillation’’ and ‘‘cardiovascular events’’. The search was confined to human studies and English language restricted. We obtained 278 articles. A trial was included if the overall study population included AF patients, it was published in a peer-reviewed journal, and major adverse coronary events (MACE) were recorded through the follow-up. A trial was excluded from our analysis if the AF population was lower than 150 subjects. Thus, 13 studies were selected according to the above-mentioned inclusion and exclusion criteria [5–17] (Table 1). In only two of these, MACE were included as primary end-points [5, 6] (Table 1A). In the first study, a very high incidence of new MACE was found in AF patients (74% during a mean follow-up of 30 months) compared with patients with a sinus rhythm (42%) or a supraventricular tachycardia (43%) [5]. These patients had a mean age of 81 years, and a clinical history complicated by CHD in [50% of cases. After controlling L. Polimeni and L. Perri equally contributed to the study.