Quantitation of myocardial fibrosis and its relation to function in essential hypertension and hypertrophic cardiomyopathy

Myocardial interstitial fibrosis is an important microscopic feature of hypertrophic cardiomyopathy. To determine whether interstitial fibrosis of the myocardium in hypertrophic cardiomyopathy and essential hypertension differ in quality or quantity, and to determine whether fibrosis affects cardiac function directly, we measured the percentage of fibrosis in patients of both categories and compared the severity of fibrosis with several cardiac functions. Left and right ventricular endomyocardial biopsies were performed in 25 patients with essential hypertension and in 19 patients with hypertrophic cardiomyopathy. Interstitial fibrosis was classified into four different microscopic types, and the percentage of total and of each type was calculated using the point-counting method. Although the percentage of total fibrosis was similar between the two groups, the type of fibrosis was different. There was no correlation between the percentage of total fibrosis and the mean size of myocytes in either group. Although there was a significant correlation between the percentage of total fibrosis and the thickness of the interventricular septum in hypertrophic cardiomyopathy, such correlation was lacking in hypertension. There was no correlation between the percentage of total fibrosis and the ejection fraction, cardiac index, or left ventricular end-diastolic pressure in either group. We concluded that the amount of myocardial interstitial fibrosis in hypertrophic cardiomyopathy is no greater than that in essential hypertension, but the type of fibrosis is different. Furthermore, in subjects in whom the ejection fraction is normal or only slightly decreased, fibrosis does not influence global cardiac functions.