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From the Division of Pediatric Endocrinology, Department of Pediatrics, Department of Cardiology, Cardiothoracic Center*, and Department of Radiodiagnosis**, All India Institute of Medical Sciences, New Delhi 110 029, India.

Reprint requests: Dr. P.S.N. Menon, Additional Professor of Pediatrics, Division of Pediatric Endocrinology and Genetics, All India Institute of Medical Sciences, New Delhi 110 029, India. Fax: 91 11 686 2663 . e-mail: psnmenon@hotmail.com

Manuscript received: July 29, 1998; Initial review completed: October 9, 1998;             Revision accepted: March 10, 1999.

Objective: To evaluate prospectively cardiac function in children with primary hypothyroidism before and after replacement therapy with L-thyroxine.
Design: Prospective clinical and laboratory cardiac evaluation of children with hypothyroidism before and after therapy.
Setting: Hospital based.
Subjects: 20 consecutive children aged 6 months - 14 years with primary hypothyroidism. Methods: Assessment of cardiac status by clinical, radiological, ECG, echocardiography, M-mode and 2 dimensional echo-Doppler study and phonocardiography for systolic and diastolic functions and structural anomalies.
Results: Indices of myocardial contractility like ejection fraction (EF), velocity of circumferential fibre shortening (VCF) did not change with therapy. However, systolic time intervals, both left ventricular (before therapy 0.32±0.03 msec; after therapy 0.25±0.03 msec; p <0.001) showed a significant change. In diastolic functions, isovolumic relaxation time fell from 62±9 msec before therapy to 50±5 msec after therapy (p <0.001). Pericardial effusion was found in 10 children before treatment which disappeared in 7 following therapy. Conclusion: Subtle evidence of alteration of myocardial function is thus seen in children with primary hypothyroidism which reverses with treatment.

Key words: Cardiac function, Echocardiography, Hypothyroidism.