Abstract 837: De Novo Atomic Force Microscopy of Intracoronary Thrombus: New Insights into Fibrin Clot Architecture and Implications for Fibrinolysis
Fibrin clot structure is associated with myocardial infarction (MI). A fibrin clot with thin, tightly packed fibers and small pores is associated with decreased fibrinolysis and poorer clinical outcome. However, data on fibrin clot structure is based on electron microscopy (EM) of fixed clots formed under in-vitro, static conditions and may not be representative of clots under physiological conditions. Data is lacking on clots formed under dynamic in-vivo conditions. The atomic force microscope (AFM) allows imaging of biological samples with sub-molecular resolution without fixation or processing. Here we present novel AFM data on the sub-molecular structure of the fibrin clot within the thrombus in MI. Thrombus was retrieved from coronary vessels during percutaneous coronary intervention of patients with acute MI (n=10) with the EXPORTTM catheter. Briefly, the thrombus retrieval system was maneuvered across a section of the coronary vessel that had been identified as having thrombus according to angiographic data, the thrombus removed and analyzed within 2– 4 hours. The thrombus was laid onto freshly cleaved mica discs and imaged with the Picoforce AFM deployed in the tapping mode. High resolution images showed structures comprising mainly fibrin meshwork with very little platelets and red blood cells. The fibrin meshwork was more disorganized than in-vitro clots, with the fibers appearing thinner and more curved (53 +/− 6.3 nm vs. 115 +/− 30 nm, n=200, p<0.03). Furthermore, there were regular occurrences of small regular pore-like structures incorporated within a fibrin fiber which has not been observed with EM due to the sputter coating process. These pores had diameters of 26 +/− 3 nm which correspond to the FXIII A dimer dimensions and could be diffusion channels that expedite FXIII crosslinking activities. At higher magnification, submolecular structures within the fibrin fibers were observed with dimensions corresponding to fibrin molecules. The tri-nodular structure of fibrin molecules could be discerned.These observations provide the first images of in-vivo thrombus architecture by AFM and evidence of diffusion channels within a fibrin fiber that may have implications for fibrinolysis and provide targets for therapeutics.