135 MYOCARDIAL FUNCTION OF THE NEWBORN WITH CONGENITAL HYPOTHYROIDISM

Abstract

Because of the known differences between newborn and adult myocardial tissue, this study was undertaken to evaluate by echocardiography the cardiovascular condition of 13 hypothyroid infants (HI), aged 3 to 9 weeks. Left ventricular (LV) systolic and diastolic dimensions, posterior wall thickness, end diastolic (EDV) and systolic volumes were all significanlty lower in the HI, compared to 23 normal infants of the same age (p < 0.05). No pericardial effusion was found. All HI had a significant bradycardia (p < 0.01) with a low cardiac output (p < 0.02). The mean velocity of circumferencial fiber shortening and the shortening fraction of LV were normal. However the pre-ejection period (PEP) was abnormally prolonged (p < 0.05) as well as the ratio PEP to left ventricular ejection time (LVET) (p < 0.01). PEP/LVET correlated inversely with EDV, suggesting that the elevated PEP/ET could partly be due to the decreased pre-load. In conclusion, the cardiovascular involvement in congenital neonatal hypothyroidism is characterized by a low cardiac output with a normal myocardial function and absence of pericardial effusion. This study confirms the concept that in hypothyriodism the cardiomegaly is essentially due to pericardial effusion.