Levothyroxine Treatment and the Risk of Cardiac Arrhythmias – Focus on the Patient Submitted to Thyroid Surgery

Abstract

Levothyroxine (LT4) is used to treat frequently encountered endocrinopathies such as thyroid diseases. It is regularly used in clinical (overt) hypothyroidism cases and subclinical (latent) hypothyroidism cases in the last decade. Suppressive LT4 therapy is also part of the medical regimen used to manage thyroid malignancies after a thyroidectomy. LT4 treatment possesses dual effects: substituting new-onset thyroid hormone deficiency and suppressing the local and distant malignancy spreading in cancer. It is the practice to administer LT4 in less-than-high suppressive doses for growth control of thyroid nodules and goiter, even in patients with preserved thyroid function. Despite its approved safety for clinical use, LT4 can sometimes induce side-effects, more often recorded with patients under treatment with LT4 suppressive doses than in unintentionally LT4-overdosed patients. Cardiac arrhythmias and the deterioration of osteoporosis are the most frequently documented side-effects of LT4 therapy. It also lowers the threshold for the onset or aggravation of cardiac arrhythmias for patients with pre-existing heart diseases. To improve the quality of life in LT4-substituted patients, clinicians often prescribe higher doses of LT4 to reach low normal TSH levels to achieve cellular euthyroidism. In such circumstances, the risk of cardiac arrhythmias, particularly atrial fibrillation, increases, and the combined use of LT4 and triiodothyronine further complicates such risk. This review summarizes the relevant available data related to LT4 suppressive treatment and the associated risk of cardiac arrhythmia.

Hormonal and inflammatory modulatory effects of hesperidin in hyperthyroidism-modeled rats

“…hyperthyroidism-modeled female rats. Hyperthyroidism-modeled animals showed a considerable increase in serum total T3, FT3, total T4, and FT3 levels along with a minor drop in serum TSH level; these results are consistent with those of Mannaa et al(1) Gluvic et al(19) and Meriem et al,(20). It has been stated that LT4 promotes thyroid activity and works primarily by inhibiting oxidative iodination within the thyroid gland to affect the synthesis of the thyroid hormones (thyroxin and triiodothyronine).…”

“…( 1 ) Gluvic et al. ( 19 ) and Meriem et al., ( 20 ). It has been stated that LT4 promotes thyroid activity and works primarily by inhibiting oxidative iodination within the thyroid gland to affect the synthesis of the thyroid hormones (thyroxin and triiodothyronine).…”

Rare case of Torsades de Pointes in severe hypothyroidism: literature review and challenges in management

“…However, there is higher mortality risk when thyroxine doses exceed 500 mg or triiodothyronine doses exceed 75 mg daily [ 8 ]. Excessive thyroid hormones are associated with adverse cardiovascular effects such as increased risks of supraventricular arrhythmia like atrial fibrillation and may precipitate heart failure, embolic stroke, or death [ 9 ]. However, Tdp, if left unchecked, can also deteriorate into ventricular fibrillation and lead to death [ 10 ].…”

Association between sensitivity to thyroid hormones and risk of arrhythmia in patients with coronary heart disease: a RCSCD-TCM study in China

“…The thyroid function has a profound effect on regulating heart rhythm [22,23]. Arrhythmia is de ned as irregular heartbeat, severely exceeding the normal range [24]. Thyroid hormones play a momentous role in cardiac electrophysiology and Ca2 + processing, which may affect cardiac function and susceptibility to arrhythmia [25].…”