Activity of left ventricular thrombi of different ages. Assessment with indium-oxine platelet imaging and cross-sectional echocardiography.

To evaluate the possible relation between the age of intracardiac thrombi and the presence and degree of their activity, 29 patients with left ventricular thrombi that developed after an anterior myocardial infarction were evaluated by means of 111In-oxine autologous platelet imaging. None of the patients was treated with anticoagulants or platelet inhibitors during either the acute phase of infarction or the follow-up. The time of appearance and the shape of left ventricular thrombi were assessed by serial cross-sectional echocardiograms, obtained within 24 hours of onset of the chest pain, every 24 hours until the fifth day, every 48 hours until the 15th day, and then every month for a follow-up of 1 to 17 months (mean: 8 months). At the time of the scintigraphic examination, left ventricular thrombi were aged 1 month in 9 patients, and 2 to 14 months in the remaining 20 patients. 111In-oxine imaging with autologous platelets was obtained in all patients at 4, 24, 48 and 72 hours, in the sagittal, 30 degrees and 45 degrees left anterior oblique projections. In 25 patients the degree of haematological activity of the thrombi was evaluated by dividing the values of thrombus activity/background activity, obtained at 4, 24, 48 and 72 hours, respectively, by the value observed at 4 hours (uptake index). Scintigraphic imaging showed the presence of an active thrombus in every patient. In the 9 patients with recent thrombi, the uptake index was significantly greater than in subjects with older ones (P less than 0.01). Hence, in patients with anterior myocardial infarction, untreated with anticoagulants or platelet inhibitors, haematologically active thrombi can be observed even more than one year after their appearance. The uptake of platelets on the surface of thrombi is greater in recent left ventricular thrombi than in older ones.