Histopathological Analysis of Intracoronary Thrombus and how it has Helped us to Understand the Pathophysiology of STEMI

Exposure of a ruptured or eroded atherosclerotic plaque to vessel lumen can lead to thrombus formation and development of ST-segment elevation myocardial infarction (STEMI). In vivo analysis by using thrombectomy systems during primary percutaneous coronary intervention (PPCI) allows to know its composition and better understanding of the pathophysiology of STEMI.

Histopathological study of the thrombus is based on its age (fresh [1 day], lytic [1-5 days] and organized [>5 days]) and macroscopic appearance (white versus red thrombus).

In vivo analysis revealed that nearly 50% of aspirared thrombi in STEMI of < 12 hours of evolution were older instead of fresh. These findings suggest that a dynamic process of rupture and repair of the atherosclerotic plaque can occur days or weeks before the formation of an occlusive thrombus. In vivo studies have also related thrombus size, red thrombus appearance, old thrombi and erythrocites and neutrophils-rich thrombi with a less ST-segment recovery post-PPCI and lower myocardial blush grade. All these and presence of plaque in the aspirated thrombi (found in 40% of cases) has been associated with the occurrence of distal embolization after the procedure, all of them poor prognosis indicators. Finally, older thrombi has been related with almost twice risk of death at 4 years post-STEMI than fresh thrombi in a large series of patients.

In conclusion, composition of coronary thrombus indicate a silent process of plaque instability that precedes STEMI for days or weeks, and its content is an important prognostic marker during and after infarction.