Adverse effect of warfarin in acute myocardial infarction: increased left ventricular thrombus formation in patients not treated with high-dose heparin.

In a prospective non-randomized study, 229 patients with a verified first acute anterior myocardial infarction (AAMI) underwent echocardiography before discharge in order to study left ventricular (LV) thrombus formation. Antithrombotic therapy was given according to the routine of each centre. Patients receiving high-dose heparin had few LV thrombi, irrespective of warfarin therapy (6/32 vs 3/25, P ns). In patients not given heparin, however, a significantly higher prevalence of LV thrombi was found in a subgroup of patients treated with warfarin as compared to those who did not receive warfarin (8/13 vs 17/68, P 0.02). A similar, but non-significant difference was observed in patients given low-dose heparin (42% vs 27%, P ns). Within the non-heparin and low-dose heparin groups, age, infarct size, occurrence of Q-wave infarction, congestive heart failure and LV wall motion impairment did not differ between those treated or not treated with warfarin. In conclusion, high-dose heparin seems effective in the prevention of LV thrombosis irrespective of warfarin therapy after AAMI. The start of warfarin therapy in patients not receiving heparin was, however, associated with an increased prevalence of LV thrombosis.