Changes in volume and density of platelets in myocardial infarction.

The distributions of platelet volume and density were measured in 15 men suffering myocardial infarction and in 22 healthy controls. The method used separated 93% of the total platelet population from whole blood. Mean platelet volume of the study group compared with that of controls was increased by a mean of 0.98 fl (p less than 0.001) in the first 12 hours after myocardial infarction, and by 1.24 fl six weeks later (p less than 0.001). Distribution of platelet volume remained log normal after myocardial infarction. Modal platelet density was increased by a mean of 25 g/l (p less than 0.05) after myocardial infarction. Platelet volume is probably chronically large in men suffering myocardial infarction and may be related to changes in megakaryocytes. It is suggested that the increase in platelet volume occurs before infarction.