CARDIAC SYSTOLIC AND DIASTOLIC FUNCTION AT REST AND EXERCISE IN SUBCLINICAL HYPOTHYROIDISM - EFFECT OF THYROID-HORMONE THERAPY

Cardiac atrial and ventricular parameters were determined by Doppler t wo-dimensional echocardiography at rest and exercise in 8 patients wit h subclinical hypothyroidism (SCH) (6 women and 2 men; age range: 28-4 8 years) before and 3 months after achievement of a euthyroid state wi th incremental adjustment of L-thyroxine therapy. None of the patients had known heart disease, At 3 months of L-thyroxine therapy, TSH leve ls decreased from 14.8+/-9.4 mIU/L to 3.0+/-1.5 mIU/L and FTI increase d from 7.1+/-1.8 to 8.1+/-1.9. The cardiac studies were performed at r est, and during incremental exercise load (50, 100, 150 W workload) on a Quinton(R) exercise bicycle. No significant differences were found between the subclinical hypothyroid and euthyroid states in systolic b lood pressure at rest (104.8+/-12.3 vs 105+/-10.1 mm Hg) and exercise (158+/-24.9 vs 158.5+/-20.9 mm Hg) or diastolic blood pressure at rest (70+/-4.7 vs 69+/-5.7 mm Hg) and exercise (86+/-11.4 vs 89.2+/-7.3 mm Hg). All echocardiographic atrial and ventricular parameters were sim ilar before and during L-thyroxine therapy with the exception of a sma ll but significant change in left ventricular diastolic dimension (4.5 +/-0.3 vs 4.8+/-0.4 cm; p <0.05). All Doppler parameters were not sign ificantly affected by L-thyroxine therapy with the exception of preeje ction period at stage III exercise (51+/-17 vs 39+/-13 msec; p <0.05). Preejection period at other stages of exercise showed trends toward s imilar differences between subclinical hypothyroidism and euthyroidism , but the differences were not statistically significant. We conclude that the cardiac structure and function overall remains for practical purposes normal in subclinical hypothyroidism. However, the latter may be responsible for a mild prolongation of the preejection period duri ng exercise and a slightly smaller left ventricular diastolic dimensio n at rest, changes that may not be of clinical significance in patient s without underlying heart disease.