Myocardial capillary supply is limited in hypertrophic cardiomyopathy: a morphological analysis.

OBJECTIVE: To clarify the morphological basis of the limited coronary reserve in hypertrophic cardiomyopathy (HCM).

BACKGROUND: Some of the symptoms in Hypertrophic cardiomyopathy (HCM), such as chest pain, dyspnea and arrhythmia, may be explained by myocardial ischemia. Many patients with HCM are known to exhibit these symptoms in the absence of atherosclerosis in the major coronary vessels. Decreased myocardial perfusion has been demonstrated in HCM, however, little is known about the myocardial capillary morphology in this disease.

METHODS: Using immunohistochemistry and morphometry, we analysed capillaries and cardiomyocytes in myectomy specimens from 5 patients with HCM with moderate hypertrophy and left ventricular outflow tract obstruction and in 5 control hearts.

RESULTS: The number of capillaries per cardiomyocyte (p<0.009) and number of capillaries per cardiomyocyte area unit, reflecting cardiomyocyte mass (p=0.009), were lower in individuals with HCM, i.e. indicating loss of capillaries. In HCM, the capillary density was 33% lower (p<0.05).

CONCLUSIONS: Our morphologic findings show that the capillary supply, and thus the coronary reserve, is impaired in HCM with moderate hypertrophy and left ventricular outflow tract obstruction. These data may partly explain the limitation of myocardial perfusion in HCM, which is associated with worse prognosis. Furthermore, we present evidence of actual loss of myocardial capillaries in HCM and a defective capillary growth.