Myocardial changes in pressure overload-induced left ventricular hypertrophy. A study on tissue composition, polyploidization and multinucleation.

Morphological changes in human myocardium associated with pressure overload-induced left ventricular hypertrophy were studied in 22 normal and 21 hypertrophic hearts obtained at autopsy. Samples were obtained from the left lateral ventricular wall, half way between the apex and the base. Myocyte dimensions, polyploidization, multinucleation and relative volume fractions were studied. Regression analysis in relation to indexed heart weight yielded statistically significant correlation coefficients for myocyte volume: r = 0.69 (P less than 0.001), for degree of polyploidization: r = 0.77 (P less than 0.001), for number of nuclei per myocyte: r = 0.47 (P less than 0.01) and for volume fraction of myocytes: r = 0.32 (P less than 0.05). Approximate numbers of myocytes and connective tissue cells per left ventricle were calculated. Correlation coefficients related to indexed heart weight were r = 0.34 (P less than 0.05) for the number of myocytes and r = 0.76 (P less than 0.001) for the number of connective tissue cells. Based on regression analysis in relation to indexed heart weight, we calculated that a doubling of indexed heart weight was associated with an increase in mean myocyte volume by 65%, degree of polyploidization by 24%, multinucleation by 7%, number of myocytes by 20% and number of connective tissue cells by 141%. The volume percentage of myocytes decreased by 6% in favour of the connective tissue fraction. These changes in myocardial composition indicate that the term 'hypertrophy' inadequately describes the actual myocardial changes in response to pressure overload.