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Developmental modulation of myocardial mechanics: age- and growth-related alterations in afterload and contractility
S D Colan1, I A Parness, P J Spevak
1Department of Cardiology, Children's Hospital, Boston, Massachusetts 02115.
Insights
Normal growth impacts heart function in children. Myocardial contractility decreases with age, while wall stress increases, especially in early childhood. This study reveals age-related changes in pediatric cardiac mechanics.
Area of Science:
- Pediatric Cardiology
- Cardiovascular Physiology
- Biomedical Engineering
Background:
- Somatic growth affects myocardial mechanics in pediatric heart disease.
- The impact of age and body size on myocardial contractility and loading conditions in healthy children is not well understood.
Purpose of the Study:
- To evaluate the effect of age and body size on myocardial contractility and loading conditions in normal infants and children.
- To characterize age-related changes in left ventricular mechanics during normal growth.
Main Methods:
- Echocardiography and phonocardiography were used to assess left ventricular function in 256 healthy children (7 days to 19 years).
- Calculated indexes included myocardial contractility (velocity of shortening) and loading conditions (wall stress).
- Subjects were stratified by age, gender, and body surface area.
Main Results:
- Ventricular shape and wall stress/dimension ratios remained constant with growth.
- Increased blood pressure with age led to a significant rise in wall stress, particularly in early childhood.
- Systolic function decreased with age, but contractility declined more than predicted by afterload, indicating higher infant contractility.
Conclusions:
- Normal growth involves an age-associated increase in myocardial wall stress due to hemodynamic load adaptation.
- Pediatric myocardial contractility exhibits a rapid age-related decline, with the highest levels observed in the youngest infants and children.
- These findings provide insights into normal cardiovascular development and may inform understanding of heart disease in children.
Abstract:
Somatic growth is associated with alterations in myocardial mechanics in children with heart disease and in most animal models of congenital heart disease. However, the effect of age and body size on myocardial contractility and loading conditions in normal infants and children is not known. Therefore, 256 normal children aged 7 days to 19 years (34% less than 3 years old) were evaluated with noninvasive indexes of left ventricular contractility and loading conditions. Two-dimensional and M-mode echocardiographic recordings of the left ventricle were obtained with a phonocardiogram, indirect pulse tracing and blood pressure recordings. Left ventricular dimensions, wall thickness and pressure measurements obtained from these data were used to calculate peak and end-systolic circumferential and meridional wall stress and mean and integrated meridional wall stress. Velocity of shortening adjusted for heart rate was compared with end-systolic stress to assess contractility independently of loading status. The subjects were stratified for gender and each of the derived variables was related to age and body surface area. Ventricular shape, assessed as the major/minor axis ratio, and the circumferential/meridional stress ratio were found to be invariant with growth. The ratio of posterior wall thickness to minor axis dimension did not change with age, despite the normal age-related increase in blood pressure. The increase in pressure despite unvarying ventricular shape and wall thickness/dimension ratio resulted in a substantial increase in wall stress that was most dramatic during the first few years of life. In association with the increase in afterload, systolic function decreased with age. However, the age-related decrease in the velocity of shortening was greater than that expected from the increase in afterload alone, indicating a higher level of contractility in infants and children during the first years of life than in older subjects. The process of normal growth and development, similar to that in children with heart disease, is associated with a rapid decrease in the trophic response to hemodynamic loads, resulting in an age-associated increase in wall stress. There is a similar but somewhat more rapid decrease in contractility, with the highest values seen in the youngest patients.