Aspirin-Myocardial Infarction Study (AMIS)

BACKGROUND:

It had been postulated that thrombosis plays a major role in the late stages of coronary artery occlusion. Platelet aggregation is a large component in the formation of arterial thrombi. Theoretically, an agent which prevents the aggregation of platelets would be of value in people with coronary artery disease. Aspirin, in small doses, inhibits platelet aggregation for prolonged periods of time, and therefore might be expected to prevent or retard the occlusion of coronary arteries. This would be reflected in a decrease in the incidence of myocardial infarction and a decrease in mortality due to coronary artery disease.

Several studies had given preliminary evidence that regular administration of aspirin may be of benefit to patients with known coronary artery disease. A National Heart and Lung Institute-sponsored study, the Coronary Drug Project, ran a pilot trial of aspirin and placebo in men with previous myocardial infarctions. Preliminary results from this trial demonstrated its feasibility and led NHLBI to sponsor a more definitive controlled study of the benefit of aspirin in the secondary prevention of coronary heart disease.

An Institute Planning Committee met four times between October 1974 and April 1975 and developed a protocol, manual of operations, and data collection forms. Recruitment of patients began in June 1975, with the first patient randomized on July 2, 1975. Patients who were randomized had been seen at the AMIS Clinical Center for two initial visits and one baseline visit and were free of any reasons for exclusion, such as the current use of anticoagulants and a history of adverse reactions to aspirin. Patients took acetaminophen at times when they would normally take aspirin.

Follow-up was for a minimum of 3 years, with each patient seen at 4-month intervals and monitored for side effects and various nonfatal events, including cardiovascular problems. The primary endpoint was mortality. Annually, a detailed history was obtained and a complete physical examination performed. The study involved 30 clinical centers, a coordinating center, and a central laboratory.

The study completed patient recruitment in the scheduled one year period. A total of 4,524 post-MI patients were enrolled by the 30 clinical centers. Three-year minimum patient follow-up ended in August 1979.

DESIGN NARRATIVE:

Randomized, double-blind, fixed sample. Eligible patients were assigned to a treatment group receiving 1 gm of aspirin daily (the equivalent of three standard aspirin tablets) or to a control group receiving a placebo.