Fibrin formation and platelet aggregation in patients with acute myocardial infarction: Effects of intravenous and subcutaneous low-dose heparin

Fibrinopeptide A (FPA) and betathromboglobulin (BTG) were measured in 42 patients with acute myocardial infarction (AMI) allocated on admission to one of three groups: 14 patients received a heparin bolus injection of 5000 IU intravenously followed by a 2-hour intravenous infusion (830 IU/hr) (group 1), 14 patients received a heparin bolus of 5000 IU subcutaneously (group 2), and the remaining 14 patients received no anticoagulant treatment (group 3). In group 1 the initially elevated FPA level of 5.8 ± 1.8 ng/ml dropped to 2.0 ± 1.5 ng/ml 30 minutes after the intravenous heparin bolus injection of 5000 IU (p < 0.001) and returned to normal (1.9 ± 0.8 ng/ml) in 8 of 14 patients. The initially elevated BTG level of 64 ± 21 ng/ml did not change significantly during intravenous heparin treatment, whereas there was a rapid but only transitory increase in platelet factor 4, (PF4) from 25 ± 9 to 74 ± 16 ng/ml (p < 0.01) after the intravenous heparin bolus. In group 2 the initial FPA of 5.0 ± 2.3 ng/ml was similarly elevated as in group 1 and dropped to 2.7 ± 1.7 and 3.3 ± 1.5 ng/ml 2 and 4 hours after 5000 IU subcutaneously (p < 0.05), whereas 6 and 8 hours after subcutaneous heparin bolus the mean FPA levels were 4.2 ± 1.7 and 5.5 ± 2.0 ng/ml and no more significantly different from the initial FPA values. BTG and PF4 did not change significantly after the subcutaneous heparin bolus. In group 3 the initially elevated mean FPA level of 4.9 ± 2.4 ng/ml did not change significantly during the first 8 hours after admission, whereas the FPA level 24 hours after admission was 8.4 ± 3.9 ng/ml and higher than the initial value (p < 0.01). We conclude that heparin may reduce the elevated FPA level in plasma found in patients with AMI; however, neither subcutaneous nor intravenous heparin n a dosage frequently used is sufficient to consistently normalize the elevated rate of fibrin formation found in these patients.