Changes in heart rate variability and QT dispersion in patients with overt hypothyroidism

Abstract

Objective: The aim of the present study was to evaluate the effect of clinical hypothyroidism on cardiovascular autonomic function and ventricular repolarization. Design and methods: We studied 31 patients (22 females and 9 males; mean age 53.6G11.8 years) with overt hypothyroidism (TSHZ56.2G14.7 mU/ml, low free thyroxine (T 4 ), free tri-iodothyronine (T 3 )) and 31 euthyroid controls, to investigate the dispersion of the QT interval in electrocardiogram (ECG) (an index of inhomogeneity of repolarization) and heart rate variability (HRV; a measure of cardiac autonomic modulation). The hypothyroid patients and controls underwent a full medical examination, standard 12-lead ECG, and 24-h ambulatory ECG monitoring. The hypothyroid patients were re-examined after 6 months of treatment with L-T 4 . Results: Patients with hypothyroidism showed higher QT dispersion and lower HRV measures than controls (P!0.01 or P!0.001). In hypothyroid patients, standard deviation of all R-R intervals was inversely related (by simple regression) to serum (log)TSH levels (rZK0.47, PZ0.008), while QT dispersion (rZ0.50, PZ0.004) and QTc dispersion (rZ0.46, PZ0.008) were directly related to (log)TSH. Parameters of HRV improved after 6 months of L-T 4 treatment, with the correction of hypothyroidism, becoming comparable with those of the control subjects, whereas the QT and QTc dispersion results were found to be only partially restored, remaining higher than the controls. Conclusions:The results of the study demonstrate that hypothyroidism is associated with a decreased sympatho-vagal modulation of the heart rate and with an increased inhomogeneity of ventricular recovery times. The assessment of HRV and QT dispersion in patients with overt hypothyroidism may represent a useful tool in monitoring the cardiovascular risks.European Journal of Endocrinology 158 85-90

Sudden cardiac arrest as a rare presentation of myxedema coma: case report

“…High plasma norepinephrine levels have been seen in hypothyroidism, but the responsiveness to endogenous catecholamine is decreased, because of a decrease in the number of beta adrenergic receptors and their desensitization to the effect of catecholamine. This autonomic dysfunction can be partly restored after replacement treatment with levothyroxine [7]. …”

Cardiac Autonomic Regulation Is Disturbed in Children with Euthyroid Hashimoto Thyroiditis

“…Canpolat et al (2011) have also shown disturbed HRV parameters in familial Mediterranean fever, another autoinflammatory disorder. Although altered cardiac autonomic balance has been shown in the hypothyroid and subclinically hypothyroid patients with Hashimoto thyroiditis, there is not any study on the evaluation of cardiac autonomic functions in euthyroid children with Hashimoto thyroiditis (Galetta et al 2008). VLDL-cholesterol (mg/dL) 17.7 ± 6.5 15.4 ± 7.4…”

“…According to some researchers, the HRV alterations in hypothyroidism and subclinical hypothyroidism can be reversed by levothyroxine therapy (Galetta et al 2006(Galetta et al , 2008. Padberg et al (2001) have reported reduction in anti-TPO antibodies and B lymphocyte counts in adults with eHT in response to levothyroxine prophylaxis.…”

“…As significant autonomic nervous system involvement and cardiovascular risks have been shown in earlier studies in both hypo-and hyperthyroid states, cardiological consultation has been part of our follow-up in children with suspected or proven thyroid diseases (Inukai et al 1998;Chen et al 2006;Galetta et al 2008). However, to the best of our knowledge, autonomic influence in euthyroid Hashimoto thyroiditis (eHT) has not yet been studied.…”

Atrial Bigeminy Associated With Hypothyroidism: A Case Report

“…In addition, hypothyroid patients are more prone to ventricular arrhythmias, due to increased electrical dispersion in the myocardium [7].…”