Double Blind Trial of Long‐term Anticoagulant Treatment After Myocardial Infarction

Abstract A prospective double blind trial of long‐term anticoagulant medication following myocardial infarction was carried out in Utrecht from May 1, 1964 to January 15, 1966. With the collaboration of all Utrecht cardiologists, all their patients with acute myocardial infarction were included in this trial after a 4‐month interval, to be distributed strictly at random over a phenprocoumon and a placebo group. Supplemental therapy and follow‐up were identical in both groups. Of the total of 138 patients included in the trial, 68 received phenprocoumon and 70 were given a placebo. One patient died in the phenprocoumon group, and eight patients died in the placebo group. This difference is significant ( P < 0.01). The difference in the number of reinfarctions was not significant (5 cases and 7 cases, respectively). After January 15, 1966, when the difference between the two groups had become significant, all patients were further treated with phenprocoumon. Nevertheless, the difference in mortality continued through 1966, with five deaths in the original placebo group and only one death in the original phenprocoumon group. The mean thrombotest level was 10.7%; patients remained within the therapeutic limits (5–15% thrombotest) during an average of 91% of the entire period of investigation. The mean daily phenprocoumon dose was 3.21 mg. No serious haemorrhagic complications occurred. The results of our study are consistent with those of several other recently published investigations. The intensity of the hypocoagulability attained is probably of decisive importance in this respect. However, correct calculation of the mean level of hypocoagulability is difficult. The fact that in the original placebo group the results remained less favourable even after the switch to phenprocoumon emphasizes the necessity of long‐term treatment with adequate doses of anticoagulants following myocardial infarction.