Byrne, John

The incidence of reinfarction, death and systemic thromboembolism is greatest in the first 2 months after acute myocardial infarction and decreases with time after infarction. Reasons for this are unknown, but increased platelet vascular wall interaction may be a contributing factor. Thirteen patients, mean age 53 years, had a platelet survival determination (platelet half-life calculated by least square analysis) within 1 month (mo) after acute, uncomplicated myocardial infarction (10 transmural, 3 subendocardial); a platelet survival study was repeated 3-8 mo (average 4 mo) later. All patients were on oral anticoagulants and during the time of observation none of the patients had any clinical thromboembolic events.Ten of the 13 patients had a shortened (<92 hours) platelet survival half-life of 75 hours (avg) within 1 mo after myocardial infarction which increased significantly (P<.01) to 94 hours (avg) four mo (avg) later. Ten control patients with angiographically proven coronary artery disease, stable angina pectoris, and a shortened platelet survival of 85 hours (avg) had a repeat platelet survival 6 mo later that was not significantly changed (mean variability 5%).The shortened platelet survival that improves with time after myocardial infarction is compatible with the increased incidence of reinfarction, death and thromboembolism early after myocardial infarction. Whether the increased platelet consumption reflects platelet deposition in the coronary vessels or in the left ventricle (as a mural thrombus) is at present under investigation with imaging of III-Indium-labeled platelets.