Heparin Neutralizing Activity in the Diagnosis of Acute Myocardial Infarction

We have previously demonstrated that, relative to controls, patients long after myocardial infarction and patients with atherosclerosis have highly significantly shorter heparin thrombin clotting times (HTCT) using platelet poor plasma; but there was considerable overlap between the two groups.We have now studied 89 patients admitted with acute chest pain. In 54 of these a firm diagnosis of acute myocardial infarction (ac-MI) was made and the HTCT was very short (mean 12.8 sees) and in 48 it was less than 16 sees. In 34 patients, ac-MI was excluded and the diagnosis was usually “angina”; the HTCT was much longer (mean 25.1 sees) and in 32 it was over 16 sees. Thus there was almost no overlap between these two groups. It is suggested that this test should be adopted as a quick and reliable further test to establish a diagnosis of ac-MI (providing other reasons for very short HTCTs can be excluded, e.g. D. I. C., and provinding the patient’s thrombin clotting time is normal).This HTCT measures non-specific heparin neutralizing activity; nevertheless the evidence suggests that it is measuring platelet factor 4 liberated from damaged or “activated” platelets into the plasma. These findings underline the probable important contribution of platelets in ac-MI.