A stereological method for estimating the total number of ventricular myocyte nuclei in fetal and postnatal hearts

An experimental protocol is presented for obtaining efficient estimates of the total numbers of myocyte nuclei in the ventricles of human hearts from archival collections. Hearts were collected postmortem from fetuses at 31-42 weeks of gestation and infants at 7 days-9 months postnatal age. Ventricles from normal and abnormal subjects were examined. Numbers of myocyte nuclei per unit volume of myocardium were estimated separately for left and right ventricles using a design-based stereological device, the physical disector (parallel pairs of sections). Absolute numbers were calculated by multiplying nuclear packing densities by myocardial volume. The latter was estimated from ventricular mass and the percentage of ventricle occupied by myocardium. The findings, albeit preliminary, suggest that (1) myocyte number may rise during the last trimester of gestation, (2) postnatal ventricular growth is probably hypertrophic and/or interstitial rather than hyperplastic and (3) whilst absolute numbers are greater in the left ventricle, the pattern of growth is similar in both ventricles. Nuclear numbers found in 2 abnormal hearts (1 from a case of sudden infant death) tended to be lower than normal.