Abstract Body (Do not enter title and authors here): Background: Microvascular dysfunction is a hallmark of hypertrophic obstructive cardiomyopathy (HOCM). Factors modulating myocardial microcirculation in response to disease phenotype require further studies. This study aims to investigate microvascular remodeling in HOCM patients using a quantitative imaging toolset that combines classical histological screening, ultrastructure assessment, 3D molecular imaging and automated segmentation of myocardial tissue specimens.
Methods: Microvascular remodeling was studied in a cohort of 20 consecutive HOCM patients who underwent septal myectomy, and 6 normal controls. Myectomy specimens were examined using histopathological staining, immunofluorescence and electron microscopy. Molecular 3D visualization was conducted using Free of Acrylamide SDS-based Tissue Clearing (FASTClear) protocol of 300 µm thick myocardial slices. Cleared slices were examined using immunostaining targeting microvascular markers; Isolectinβ4 and CD31. Reconstructed images of stained slices were analyzed using ImageJ and Python-based algorithm. Transcriptome data from HOCM patients’ myocardial tissues was analyzed to investigate angiogenesis and hypoxia-related gene expression. Gene and protein expression was validated using RT-PCR and immunohistochemical staining.
Results: Histopathological examination demonstrated a significant increase in perivascular fibrosis around intramural vessels in HOCM myocardial tissues, compared to controls, associated with a significant increase in vascular wall thickness, which led to a reduction in luminal area. Electron microscopy analysis revealed, for the first time, ultrastructural changes in the microvasculature in HOCM, including irregular microvessels, disorganized perivascular collagen fibres and abnormal endothelial cell morphology. Increased Aurora and Caspase 3 levels in the endothelial cells of myocardial microvessels were observed. 3D molecular imaging of myocardial slices showed a significant reduction in microvascular density, length, and number of microvascular branches in HOCM, which correlated to LVOT. Microvascular orientation was significantly altered throughout slices of HOCM myocardium. Transcriptome data analysis and protein examination revealed that angiogenesis and hypoxia-related markers elevate in HOCM patients’ myocardial tissues.
Conclusion: Structural alterations of coronary microvasculature delineate the clinical presentation and myocardial functional response in HOCM patients.