Ventricular myocardium in control and growth-retarded human fetuses: growth in different tissue compartments and variation with fetal weight, gestational age, and ventricle size.

The aim of this study was to assess the growth of different tissue compartments in ventricular myocardium of control and intrauterine growth-retarded (IUGR) human subjects. Stereological counting and sizing methods were applied to cross-sectional samples of hearts collected post mortem at 16 to 35 (control) and 32 to 42 (IUGR) gestational weeks. Total tissue volumes and total numbers of myocyte, connective tissue, and endothelial cell nuclei were estimated. In control hearts, the volume of each tissue compartment increased linearly over the period of gestation, and this was due to proliferation, because in each case the tissue volume per nucleus remained constant. In IUGR subjects, fetal weight, ventricle volume, myocyte volume, connective tissue volume, and endothelial nuclear number were less than expected for gestational age up to at least 35 weeks. Between this age and 8 postnatal weeks, these variables are predicted to achieve equivalence with values found in control fetuses. Similar deficits were found when variables were related to fetal weight, and it is predicted that equivalence with control values would be reached at weights of between 2.3 and 3.6 kg. No such differences between groups were detected when variables were related to ventricle size. These findings indicate that growth deficits in cardiomyocytes are accompanied, and may be influenced, by developmental delays that involve the intramyocardial interstitium (capillary bed, endothelium, and surrounding connective tissues). The delays and deficits exhibit "catch-up" to control values between 35 weeks and term.