Cardiac function in congenital hypothyroidism: impairment and response to L-T4 therapy.

Electrocardiograms (heart rate, QRS voltage, QRS axis in the frontal plane. Q-Tc interval) echocardiograms [left ventricular fractional shortening (LVFS); preejection period (PEP); PEP/left ventricular ejection time (PEP/LVET) ratio; end-diastolic left ventricular free wall and interventricular septum thickness; presence of pericardial effusion], and thyrotropin (TSH), thyroxine (T4), and triiodothyronine (T3) serum levels were evaluated before and 1 week, 1 and 2 months after the start of L-thyroxine (L-T4) therapy in 11 infants with congenital hypothyroidism (CH), aged 16-59 days when first seen. Before the start of therapy, infants with CH had significantly lower QRS complexes and LVFS and significantly higher values for Q-Tc, PEP, and PEP/LVET than normal infants of the same age. The QTc interval, PEP and PEP/LVET ratio of infants with CH were significantly greater before than 1 week after L-T4 therapy, and LVFS was significantly lower before than 1 month after L-T4 therapy. Four of the infants with CH had small pericardial effusions, which disappeared within the first week of therapy. QRS axis in the frontal plane, Q-Tc interval, and PEP were negatively correlated with logT4 and logT3 serum levels. PEP/LVET ratios were negatively correlated with logT4 serum values. The QRS voltage values were positively correlated with logT4 and logT3 serum values. The frontal-plane QRS axis, Q-Tc interval, and PEP/LVET ratio were positively correlated with logTSH serum levels. The QRS voltages were negatively correlated with TSH serum levels.(ABSTRACT TRUNCATED AT 250 WORDS)