Morphometric quantification of myocyte dimensions validated in normal growing rat hearts and applied to hypertrophic human hearts.

To obtain quantitative information on changes in myocyte size in hearts with increased myocardial mass light microscopical morphometry was used in fixed and stained myocardial tissue sections. A modification of the azan staining procedure made longitudinal (sarcolemma) and transverse (intercalated discs) boundaries visible with a contrast that allowed morphometric analysis. The method was validated in left ventricular tissue of rats ranging in age from 4 to 17 weeks. Myocyte width, cut surface area, length, and volume were significantly correlated with left ventricular weight with residual errors of 5%, 5%, 6%, and 8% respectively. The method was applied to 21 human hearts, nine of which had left ventricular hypertrophy. Myocyte width, area, length, and volume both in subepicardial and subendocardial left ventricular tissue were significantly greater in hypertrophic than in normal hearts. Although the mean weight of the hypertrophic hearts exceeded that of normal hearts by 40%, myocyte volumes in subepicardial and subendocardial left ventricular tissue of hypertrophic hearts were higher by 78% and 43% respectively, indicating a transmural difference in the extent of myocyte hypertrophy. The method is accurate and reproducible and gives useful quantitative information on changes in myocyte dimensions during normal cardiac growth as well as in cardiac hypertrophy.