Background: Although several radiological imaging techniques have demonstrated the existence of microvascular coronary abnormalities in patients with hypertrophic cardiomyopathy (HCM), a detailed histopathologic assessment is lacking. We had the opportunity to analyse explanted hearts of end-stage (ES) HCM and surgical samples of patients undergoing septal myectomy for obstructive HCM.
Purpose: To assess and compare histopathologic characteristic of patients with obstructive HCM versus ES-HCM.
Methods: Surgical samples of 27 patients who underwent septal myectomy for obstructive HCM and 30 explanted hearts for ES-HCM were retrospectively analysed. Myocardial fibrosis extent was determined by a histomorphometric quantitative analysis using a dedicated software; types of fibrosis were qualitatively assessed and classified as “replacement” (scar-like) and “interstitial” myocardial fibrosis. Coronary arterioles were evaluated separately according to lumen diameter: 100–500 micron and <100 micron. For each specimen the presence of microvasculopathy, including tunica media hypertrophy and/or fibrosis as well as intimal abnormalities, was evaluated in a semi-quantitative manner. Microvasculopathy was classified as mild if generating a lumen stenosis <30%, moderate >30% and <60%, severe >60%. Myocyte abnormalities were evaluated considering hypertrophy, myofibrillar disarray and vacuolization. For the purpose of this comparative study only anterobasal septum of ES-HCM explanted hearts was considered.
Results: Mean age of our population was 46.8±12 in transplanted patients and 45.4±13.5 in patients who underwent septal myectomy. The average amount of fibrosis in the anterobasal septum of explanted hearts was 36.8% ± 20.4 as opposed to 12.8% ± 8.46 of post-myectomy surgical samples (p<0.001). Type of fibrosis was also different between subgroups: replacement in 53.3% of ES-HCM vs 14.8% in myectomies specimens (p=0.005), interstitial in 26.7% of anterobasal septum of explanted hearts vs 81.5% in myectomies samples (p<0.001). Almost all specimens showed alterations of 100–500 micron coronary arterioles (93.3% ES-HCM and 100% in myectomies); the majority of specimens showed involvement of both tunica media and the intimal layer (80% ES-HCM, 77.8% myectomies). Approximately one quarter of cases showed severe 100–500 micron arterioles stenosis (30% explanted hearts, 25% myectomies). Microvasculopathy of smaller coronary arterioles (<100 micron) was less frequent however without significant differences between subgroups (73.3% ES-HCM, 77.8% myectomies). Diffuse myocyte vacuolization was detected only in ES-HCM specimens (23.3% vs 0, p=0.011).
Conclusions: Microvascular coronary disease is frequent in all the spectrum of HCM and involves both medial and intimal layers. Although interstitial fibrosis is present in both ES-HCM and myectomies samples, scar-like fibrosis along with advanced myocyte abnormalities are distinctive patterns of ES patients.