Histopathological comparison of intramural coronary artery remodeling and myocardial fibrosis in obstructive versus end-stage hypertrophic cardiomyopathy

Background: Although imaging techniques have demonstrated the existence of microvascular abnormalities in hypertrophic cardiomyopathy (HCM), a detailed histopathological assessment is lacking as well as a comparison between different phases of the disease. We aimed to compare microvasculopathy and myocardial fibrosis in hypertrophic obstructive cardiomyopathy (HOCM) versus end-stage (ES) HCM. Methods: 27 myectomy specimens of HOCM patients and 30 ES-HCM explanted hearts were analyzed. Myocardial fibrosis was quantitatively determined with dedicated software and qualitatively classified as scar-like or interstitial. Intramural coronary arteries were evaluated separately according to lumen diameter: 100–500 μ versus <100 μ. Microvasculopathy assessment included the description of medial and intimal abnormalities and stenosis grading. The two subgroups were compared considering only the anterobasal septum of ES explanted hearts. Results: Median value of fibrosis in the anterobasal septum of explanted hearts was 34.6% as opposed to 10.3% of myectomy specimens (p < 0.001). Scar-like fibrosis was widely found in ES hearts while interstitial fibrosis was distinctive of HOCM (p < 0.001). All slides showed 100–500 μ microvasculopathy without any differences between subgroups in terms of lumen narrowing, extent of the disease and type of parietal involvement. Among ES hearts these lesions were associated with scar-like fibrosis (p = 0.034). <100-μ microvasculopathy was also frequent with no differences between subgroups. Conclusions: Microvasculopathy is an intrinsic feature of HCM with similar characteristics across the natural phases of the disease. Conversely, myocardial fibrosis changes over time with ES hearts showing a three-fold greater amount, mainly scar-like. ES showed a closer association between microvasculopathy and replacement fibrosis.