GENDER DIFFERENCES IN LEFT-VENTRICULAR GROWTH

Because the number of human cardiac myocytes is determined in infancy, subsequent increases in left ventricular (LV) muscle mass reflect cellular enlargement (hypertrophy). To determine whether the greater LV mass in adult men than in women reflects sex differences that are present throughout development or disproportionate LV growth during puberty in men, we compared echocardiographic LV mass in 333 female and 278 male normal-weight, normotensive subjects from 4 months to 70 years of age. Only a small sex difference in LV mass (mean=6%) existed before age 12 years, whereas in all older-age strata LV mass in men was 25% to 38% greater than that in women (P<.02 to P<.0001). The divergence in LV mass between male and female adolescents closely paralleled differences in height and weight and was due to proportional increases in LV chamber dimension and wall thickness in males (with no sex difference in relative wall thickness). LV mass grew less rapidly from infancy through childhood than did body size, assessed by body weight or height(2.7), yielding a reduction of LV mass/body size ratios up to puberty, which was followed by gradual increases during adulthood. Indexation of LV mass by body weight or height(2.7) but not by body surface area or height markedly reduced the sex differences in LV mass/body size ratios from puberty through the seventh decade of life. Thus, before puberty, LV mass is only modestly higher in boys than in girls. Most of the sex difference in adult LV mass follows differences in body size and is due to a greater ''physiological'' LV hypertrophy in men than in women.