SYSTOLIC TIME INTERVALS (STI) AS INDICATORS OF MYOCARDIAL THYROID HORMONE EFFECT

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Abstract
Systolic time intervals consisting of indices of electromechanical systole (QS2-I), left ventricular ejection time (LVET-I) and pre-ejection period (PEP-I) were calculated serially during therapy in 12 euthyroid, 9 hypothyroid and 9 hyperthyroid individuals. These parameters were analyzed sequentially together with the changes in serum thyroxine (T4), triiodothyronine (T3) and thyrotropin (TSH) in order to determine the sensitivity of these non-invasive procedures in monitoring peripheral thyroid hormone effect. The results are expressed in mean .+-. SEM [standard error the mean] QS2-I (506.3 .+-. 8.2 ms) and PEP-I (102.9 .+-. 4.2) were shorted (P < 0.02 and P < 0.001, respectively) in hyperthyroidism and prolonged (579.3 .+-. 7.3 and 169.6 .+-. 3.6 ms) in hypothyroidism (P < 0.01 and P < 0.001, respectively) compared to euthyroid controls (538.1 .+-. 8.8 and 130.3 .+-. 5.3 ms), while LVET-I did not significantly change in either condition. Simultaneous determinations of circulating T4, T3 and TSH showed changes appropriate to both hypo- and hyperthyroid states. In 2 patients with T3-thyrotoxicosis, PEP-I was decreased to an average of 103.1 ms, while in 2 patients with compensated hypothyroidism (normal T4 but elevated TSH) this was prolonged to 163.7 ms (average) compared to euthyroid controls. During treatment the hypothyroid group showed significant sequential correlation of TSH and PEP-I. In the hyperthyroid individuals, PEP-I correlated significantly with T4 and T3. PEP-I may be a useful, sensitive, quantitative biologic indicator of thyroid hormone effect on myocardial function.

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