Microvascular Rarefaction and Myocardial Fibrosis in Hypertrophic Obstructive Cardiomyopathy

BACKGROUND: Hypertrophic obstructive cardiomyopathy (HOCM) is a myocardial disease characterized by fibrosis and microvascular ischemia. Microvessels play a critical role in myocardial fibrosis in HOCM. However, it remains unclear whether or not myocardial fibrosis is associated with microvascular density (MVD) changes. OBJECTIVE: The aim of the present study was to investigate whether a reduction in MVD is related to myocardial fibrosis in HOCM cardiac samples. METHODS: We analyzed MVD and fibrosis in myectomy left ventricular (LV) septal wall specimens from 53 HOCM patients. Control myocardium from the LV septal wall was collected at autopsy of 9 individuals who died of noncardiac causes. RESULTS: The fibrosis ratio (% area) in HOCM was higher and the MVD was lower than that in control subjects (i.e., 12.7 ± 10.0 vs. 4.0 ± 1.4%, p = 0.012, and 480.9 ± 206.7 vs. 1,425 ± 221/mm2, p < 0.001). Patients with mild fibrosis had a higher MVD than patients with moderate fibrosis (i.e., 568.2 ± 214.8 vs. 403.2 ± 167.8/mm2, p = 0.006) and patients with severe fibrosis (i.e., 568.2 ± 214.8 vs. 378.6 ± 154.0/mm2, p = 0.024). Furthermore, a significant negative correlation was found between myocardial fibrosis and MVD in HOCM patients (r = -0.40, p = 0.003), which was also found in mild fibrosis (r = -0.40, p = 0.043), moderate fibrosis (r = -0.50, p = 0.024), and severe fibrosis (r = -0.24, p = 0.61), although no significant differences were observed in severe fibrosis. Additionally, we demonstrated that late gadolinium enhancement was negatively correlated with MVD (r = -0.37, p = 0.03) and positively correlated with fibrosis (r = 0.44, p = 0.01). CONCLUSION: HOCM patients had a higher myocardial fibrosis ratio and a lower MVD. The severity of myocardial fibrosis was negatively correlated with MVD in HOCM. These findings showed that a reduced MVD may contribute to myocardial fibrosis in HOCM.