Clinical trials versus clinical practice in the secondary prevention of myocardial infarction

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Abstract
To examine whether the results of trials on the secondary prevention of myocardial infarction have led to a change of prescription practice, the discharge forms of a random sample of 737 patients admitted to a university hospital with a diagnosis of acute myocardial infarction (MI) with Q wave from 1982 to 1988 were examined. Information about cardiovascular and other risk factors, contraindications, and prescription of β-adrenoceptor antagonists (βAA), acetylsalicylic acid (ASA) and calcium channel blockers (CCB) was collected. The prescription of these drugs was analysed in relation to clinical variables and the date of patients' discharge from hospital. During the 7 years of follow-up, the prescription of βAA increased gradually from 20% to 30–35%; the prescription of CCB was above 30% during the same period and did not change significantly with time. The prescription of ASA increased from 0% to 30–35% in the last 3 years of follow-up. Contraindications to βAA were present in 23.2% of cases and contraindications to ASA in 14.4%. In a multivariate analysis, hypertension (odds ratio 2.29, 95% confidence interval 1.55–3.38) and the period 1986–1988 (OR 2.27, 95% CI 1.57–3.30) were associated with the prescription of βAA, although the prescription of βAA decreased significantly with advancing age. Other variables inversely associated with the prescription of βAA were contraindications (OR 0.41, 95% CI 0.24–0.66) and the presence of heart failure during admission (OR 0.08, 95% CI 0.03–0.20). The prescription of CCB was inversely associated with the prescription of βAA (OR 0.41, 95% CI 0.27–0.63); the preference for CCB over βAA was notable among patients with the following characteristics: age > 70 years (39.3% vs 9.3%) angina (51.6% vs 24.7%), heart failure during admission (25.5% vs 3.2%), and contraindications to the use of βAA (28.1% vs 11.1%). The only clinical variable which was significantly (and inversely) associated with the prescription of ASA was the presence of contraindications (OR 0.13, 95% CI 0.04–0.41). These results suggest that clinical trials on the secondary prevention of ischaemic heart disease have had some influence on cardiologists' prescription habits. However, they document a large underuse of efficacious drugs such as βAA and ASA, especially among the elderly and among those patients with more severe cardiovascular disease. The frequent prescription of CCB recorded in the present study, in spite of their unproven efficacy in this condition, suggests that these drugs are often preferred to βAA for the survivors of an acute MI, especially in certain groups of patients.