Cardiac extracellular matrix at microvascular obstruction area after reperfused myocardial infarction: a morphometric study

Abstract Background Extracellular matrix (ECM), a structural and biomechanical support to cardiomyocytes, suffers substantial alterations after myocardial infarction (MI). Despite a complete reopening at epicardial level, hypoperfusion within the infarcted myocardium, known as microvascular obstruction (MVO), occurs. Extensive clinical studies and meta-analysis reported the association between the magnitude of MVO and the appearance of adverse remodeling; thus, scrutinizing ECM composition within the infarcted areas with impaired tissue-level reperfusion could provide fundamental insight regarding MVO pathophysiology. Purpose To histologically compare ECM composition within the infarct zone regarding the presence or absence of MVO using an experimental swine model of reperfused MI. Methods MI was induced in swine (n=10) by transitory 90-min coronary occlusion followed by 7 days of reperfusion. Prior to euthanasia, intracoronary thioflavin-S was infused. Within the infarcted myocardium, regions displaying MVO (thioflavin-S-) or no MVO (thioflavin-S+) were isolated and stained to morphometrically compare ECM composition. Results Regarding cellularity, areas with MVO displayed an enlarged presence of neutrophils and lymphocytes, whilst no differences in the amount of macrophages and myofibroblasts were detected in comparison to no MVO-myocardium. Those regions with macroscopic MVO showed lower capillary density than those without MVO. According to the fibers and ground substance, a significant reduction in the extension of type I collagen, laminin, and fibronectin together with an augmentation of glycosaminoglycan were noted in areas showing MVO compared to those without microvascular injury. No changes in the amount of type III collagen was observed. Conclusion The ECM composition in infarcted regions with MVO displays a higher presence of inflammatory infiltrate and glycosaminoglycans as well as a reduced amount of microvessels and fibers compared to those areas without microvascular hypoperfusion. These characteristics might underlie the development of adverse ventricular remodeling in MI patients with extensive MVO.