Myocardial growth before and after birth: clinical implications

Abstract

Perinatal changes in myocardial growth have recently evoked considerable interest with regard to cardiac chamber development with congenital cardiac lesions and to myocardial development in preterm infants. It is suggested that cardiac chamber development is influenced by blood flow. Experimental pulmonary stenosis in fetal lambs may induce either greatly reduced or markedly increased right ventricular volume. Ventricular enlargement appears to be associated with a large ventricular volume load resulting from tricuspid valve regurgitation. A small competent tricuspid valve is associated with reduced flow through the ventricle due to outflow obstruction and a small right ventricle. Postnatal growth of the ventricles in congenital heart disease is discussed. Increase in myocardial mass prenatally is achieved by hyperplasia, both during normal development and when myocardial mass is increased by right ventricular outflow obstruction. Postnatally, increases in myocardial mass with normal growth, as well as with ventricular outflow obstruction, are largely due to hypertrophy of myocytes. Myocardial capillary numbers do not increase in proportion with myocyte numbers in ventricular myocardium in association with outflow obstruction. The postnatal effects of these changes in congenital heart lesions are considered. Studies in fetal lambs suggest that the late gestational increase in blood cortisol concentrations is responsible for the change in the pattern of myocardial growth after birth. The concern is raised that prenatal exposure of the premature infant to glucocorticoids, administered to the mother to attempt to prevent hyaline membrane disease in the infant, may inhibit myocyte proliferation and result in a heart with fewer than normal myocytes. This would necessitate that each myocyte would have to hypertrophy abnormally to achieve a normal cardiac mass postnatally.

?2 Adrenoceptor gene therapy ameliorates left ventricular dysfunction following cardiac surgery

“…However, neonates may have a reduced immune response to the vector, and it is also known that the pattern of heart growth by myocyte hyperplasia changes to hypertrophy during the perinatal period [14]. Therefore, further studies must be performed in adult animals before extrapolating the current results to adults.…”

“…However, neonates may have a reduced immune response to the vector. In addition, the pattern of heart growth by myocyte hyperplasia changes to hypertrophy during the perinatal period which may also have implications for the uptake and distribution of the adenoviral vector [14].…”

Preeclampsia, prematurity and cardiovascular health in adult life

“…During this period, cardiac size increases primarily via an increase in the number of mononucleated myocardial cells [34]. At birth, there is a switch in cardiomyocyte phenotype from a foetal hyperplastic pattern to neonatal hypertrophic response.…”

Effects of Chronic Hypoxia on Fetal Coronary Responses

“…During early embryonic and fetal development, the heart mass increases primarily by an increase in cell number (hyperplasia) (Hudlicka and Brown, 1996;Page et al, 1998;Barbera et al, 2000;Rudolph, 2000).…”