Age-related variations of left ventricular endocardial and midwall function in healthy infants, children, and adolescents.

Background: In pediatric age echocardiographic evaluation of left ventricular systolic function is usually based on indexes obtained by measurements at the endocardial level. In the presence of ventricular hypertrophy this may lead to an overestimation of systolic function. The aim of this study was to assess the developmental changes of left ventricular systolic mechanics measured at the endocardial and midwall levels.

Methods: In 239 normal subjects divided into six age groups we measured left ventricular end-diastolic volume, mass and mass/volume ratio, fractional shortening, and rate-corrected mean velocity of circumferential shortening at the endocardial and midwall levels. Endocardial meridional end-systolic stress and midwall circumferential end-systolic stress were considered as indexes of afterload. Relations of extent and velocity of fiber shortening to afterload at the endocardial and midwall levels were used to assess left ventricular contractility.

Results: Blood pressure, left ventricular afterload, volume and mass increased, whereas the mass/volume ratio remained stable during growth. Fractional shortening and mean velocity of circumferential shortening at the endocardial level decreased and showed an inverse relation to afterload. Midwall fractional shortening and rate-corrected mean velocity of circumferential shortening were lower during the first months and did not change during the first year of life.

Conclusions: Left ventricular volume and mass increase with age, mass/volume ratio remains almost constant while afterload increases. Endocardial systolic function indexes are higher in the first period of life, due to low afterload and increased mass/volume ratio. In the first months of life the left ventricular myocardium shows a greater sensitivity to changes in afterload and a reduced contractility measured at the midwall level.