Left ventricular mechanics in the normal newborn.

The transition from fetal to neonatal circulatory status is accompanied by marked alteration in relative right and left ventricular systolic and diastolic pressure. These alterations would be expected to influence both global and regional performance of the left ventricle. To address this issue, sequential two-dimensional echocardiographic studies were performed in normal newborns during the first days of life. Global and regional left ventricular wall motion were quantified by computer digitization with the use of an automated edge detection algorithm and a floating-center-of-mass model. Comparison was made with a control group of normal infants and young children and the sequential change over the first 5 days of life was assessed. Newborns were found to have a circular left ventricular configuration at end-diastole beginning on day 1. At end-systole, however, there was significant left ventricular distortion due to septal flattening, which persisted until day 3 and resolved entirely by day 5 of life. Regional wall motion analysis demonstrated a corresponding augmentation of septal and contralateral left ventricular free wall systolic movement during the first days of life, with a normal pattern attained by day 4. Due to the nonhomogeneity of the left ventricular wall motion in the first few days of life, standard single-dimension shortening fraction provided an unreliable measure of global left ventricular performance before day 4. Thus, systolic right ventricular hypertension at a level sufficient to distort the left ventricular configuration is present until day 4 or 5 of life, resulting in altered left ventricular regional wall motion. As a result, usual M mode echocardiographic assessment of left ventricular function is unreliable in this age group.(ABSTRACT TRUNCATED AT 250 WORDS)