Histopathology of aspirated thrombi during primary percutaneous coronary intervention in patients with acute myocardial infarction

Thrombus aspiration in the setting of primary percutaneous coronary intervention is a recently recommended technique that facilitates thrombus removal from the culprit lesions in acute myocardial infarction (AMI) patients. Thrombectomy specimens from 50 patients with symptoms of AMI lasting usually not more than 12 h were examined by methods of routine histology, immunohistochemistry (IHC), and electron microscopy (ELMI). In 36 patients, there were fresh thrombi, in 10 older thrombi (8 of them with simultaneous presence of a fresh thrombi) and in 3 atheroma material only (in additional 7 patients atheroma material was admixed to the thrombi), and in one patient, there was carcinoma embolus. To help to distinguish between fresh and older thrombi, we recommend IHC (presence of macrophages and endothelia) and ELMI (loss of density of the erythrocyte matrix and presence of macrophages). On the other hand, changes of neutrophils (IHC degranulation/lysis) and of platelets (ELMI degranulation) appear early and thus contribute little to distinguishing between fresh and older thrombi. It could be concluded that, in a substantial proportion of patients with AMI, there is a discrepancy between duration of the symptoms and microscopic picture of the coronary thrombus. The thrombus may apparently be symptomless for a period of days or even weeks.