Systolic Time Intervals: A Valuable Parameter of Thyroid Function

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Abstract
Conventional systolic time interval measurements were made in 49 patients presenting with hypertyroidism, euthyroidism, or hypothyroidism. A linear correlation was observed over the entire range of thyroid function ( r = 0.75) between Δ PEP and the serum free T4 index. A linear correlation was also found between the PEP/LVET ratio and the serum free T4 index ( r = 0.70). A higher correlation was found between the PEP/LVET ratio and the serum free T4 index when plotted logarithmically ( r = 0.75). During treatment of hyperthyroidism, the PEP progressively lengthens and the PEP/LVET ratio increases, whereas during treatment of hypothyroidism the PEP shortens progressively to normal values while the PEP/LVET ratio diminishes. In amiodarone-induced hyperthyroidism, both a prolonged PEP and an increased PEP/LVET ratio were found. These controversial measurements, suggesting a diminished cardiac contractility, may be explained by a worsened cardiac ischemia due to the development of hyperthyroidism. Systolic time interval measurements appear to be a valuable tool in the assessment of the cardiac response to thyroid hormone during both hypothyroidism and hyperthyroidism.