Systolic Time Intervals (Sti) as Indicators of Myocardial Thyroid Hormone Effect

Systolic time intervals consisting of indices of electromechanical systole (QS 2 -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 (T 4 ), triiodothyronine (T 3 ) and thyrotrophin (TSH) in order to determine the sensitivity of these non-invasive procedures in monitoring peripheral thyroid hormone effect. The results are expreseed in mean ± sem . QS 2 -I (506.3 ± 8.2 ms) and PEP-I (102.9 ± 4.2) were shortened ( 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 change significantly in either condition. Simultaneous determinations of circulating T 4 , T 3 and TSH showed changes appropriate to both hypo- and hyperthyroid states. In 2 patients with T 3 -thyrotoxicosis, PEP-I was decreased to an average of 103.1 ms, while in 2 patients with compensated hypothyroidism (normal T 4 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 T 4 and T 3 . PEP-I may be a useful, sensitive, quantitative biologic indicator of thyroid hormone effect on myocardial function.