Optical and Scanning Electron Microscopy Thrombus Findings in Patients with STEMI Undergoing Primary Versus Rescue PCI.

: The mechanisms underlying fibrinolysis failure in patients with STEMI who are undergoing a pharmacoinvasive strategy appear to be multifactorial and may be associated with the thrombus's architecture and composition. : We aimed to compare the thrombus composition in patients with STEMI who were undergoing rescue percutaneous coronary intervention (rPCI) versus primary PCI (pPCI) using optical microscopy (OM) and scanning electron microscopy (SEM). Methods: Fifty-three patients were prospectively enrolled, with twenty-five undergoing rPCI and twenty-eight undergoing pPCI. After thrombus aspiration, each harvested fragment was divided into two pieces: one was analyzed using OM with a 60× magnifying lens on hematoxylin-eosin-stained samples, and the other with SEM at 5000× magnification. : Patients who underwent rPCI had significantly higher C-reactive protein levels and a longer ischemic interval at admission compared to those treated with pPCI (9.92 h [range: 1.58-106.17] vs. 2.14 h [range: 0-48]; < 0.001). Optical microscopy analysis revealed that thrombi from rPCI patients exhibited a significantly higher erythrocyte area percentage (18.36% [range: 0.3-50.08] vs. 0.91% [range: 0-70.1]; = 0.001), a lower fibrin content as assessed by optical microscopy (79.49% [range: 49.2-98.25] vs. 94.43% [range: 29.19-99.92]; = 0.006), and a greater amount of cholesterol crystals as measured by SEM (1.73 μm [range: 0-18.51] vs. 0.08 μm [range: 0-0.71]; < 0.001). : The thrombus composition of patients with STEMI who are undergoing rPCI had higher amounts of erythrocytes and cholesterol crystals and a lesser area occupied by fibrin compared to those undergoing pPCI. The composition of thrombi in rPCI could potentially contribute to the failure of fibrinolytic therapy within a pharmacoinvasive strategy.