Effect of Subclinical Thyroid Disease on Cardiac Function in Patients on Thyroid Replacement Therapy as Assessed by Radionuclide Ventriculography

Abstract

Objective:The evidence indicates that the cardiovascular system responds to the minimal but persistent changes in circulating thyroid hormone levels, which is typical of individuals with subclinical thyroid dysfunction. However, there is no study to compare between control or euthyroid and subclinical thyroid cases with tong-term L-thyroxine therapy regarding cardiac function of the heart using radionuclide ventriculography. The objective of our study is to assess and compare the left ventricular function through the evaluation of the radionuclide systolic parameters, diastolic parameters and heart rate for these conditions. Methods: Ten healthy controls and 32 patients with surgically treated differentiated thyroid carcinoma followed by radioactive iodine ablation and receiving suppressive L-thyroxine were evaluated by gated radionuclide ventriculography. The patients were divided into 3 groups according to their thyroid hormone profile. These groups were: euthyroid, subclinical hypothyroid, subclinical hyperthyroid groups. Results: Long-term L-thyroxine therapy significantly affected the left ventricular systolic function in patients with subclinical thyroid dysfunction. It prolonged TPER and TPFR in patients with subclinical hypothyroid dysfunction while it decreased TPER and TPFR in patients with subclinical hyperthyroid dysfunction. However, there was no effect on the euthyroid group. Conclusions: These abnormalities in cardiac function in subclinical hypo-or hyperthyroidism may lead to long-term effect on patient's lives. Early effective and accurate treatment for these patients is important to avoid the consequences of long term exposure of the cardiovascular system to small increases or decrease of thyroid hormone.