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Abstract
To study the effect of various valvular heart diseases on the quantitative histology of myocardium, 38 human hearts with valvular lesions were examined (11 aortic stenoses, nine mitral stenoses, nine mitral incompetences and nine combined aortic and mitral valve lesions). The control group consisted of ten hearts without any valvular lesions. With morphometrical methods the volume fractions of myocardial components (myocardial fibres, interstitial space and diffuse connective tissue), the numerical density of arterioles and the mean fibre diameter were estimated.
Myocardial fibrosis was more severe in hearts with valvular lesions than in the controls (5.4% vs 3.3%, P<0.01), but did not correlate with the anatomical severity of the valvular lesions. The most severe myocardial fibrosis was found in hearts with mitral imcompetence (6.7%). Fibre hypertrophy was most severe in hearts with aortic stenosis and in hearts with mitral incompetence (22 urn and 23 urn, respectively). In hearts with severe valvular lesions the mean fibre diameter was 23 u.m and in hearts with mild to moderate lesions 19 urn (P<0.01). Good correlation was observed between the mean fibre diameter and the weight of the left ventricle (A = 0.81, P<0.01). The volume fractions of connective tissue and interstitial space were significantly higher and the volume fraction of myocardial fibres was correspondingly lower in the subendocardium than in the subepicardium in hearts with either pressure overload (aortic stenosis) or volume overload (mitral incompetence). In conclusion, myocardial fibrosis occurs in patients with various valvular lesions, but the severity of the fibrosis does not correlate with the anatomical severity of valvular lesions. Marked transmural differences were observed in the volume fractions of myocardial components between the subendocardium and the subepicardium in patients with aortic stenosis and in patients with mitral incompetence. These transmural differences should be taken into account when endomyocardial biopsies are used in clinical practice.