Observations on blood viscosity changes after acute myocardial infarction.

Serial blood rheologic measurements were made in 25 patients with acute myocardial infarction; measurements included blood and plasma viscosities, hematological data and plasma protein concentrations. The blood viscosity was elevated on admission and for more than 21 days after acute myocardial infarction. However, the cause of the elevated viscosity was changed as a function of time after acute myocardial infarction. During the first three days after admission, the high blood viscosity was mainly attributable to high hematocrit values. Thereafter, the hematocrit fell, but blood viscosity remained high. High blood viscosity after the first three days of acute myocardial infarction can be correlated with increases in plasma viscosity and red cell aggregation, which in turn are explained by elevations of alpha 2 globulin and fibrinogen concentrations. Patients with higher blood viscosity on admission had a significantly higher incidence of complications, i.e., shock, thromboembolism and left ventricular failure.