Cardiovascular changes in horses with atrial fibrillation and high thyroid hormone concentration: a case–control study

Diagnosis and management of thyroid disorders and thyroid hormone supplementation in adult horses and foals

“…A negative energy balance will result in downregulation of the resting metabolic rate and circulating thyroid hormone concentrations 8 Transport Short road transport has been reported to be associated with higher fT3, tT4 and fT4 concentrations 115 Exercise Prolonged (endurance) exercise can lead to a decrease in circulating thyroid hormone concentrations 112 Drug Phenylbutazone, glucocorticoids and other drugs may decrease circulating thyroid hormone concentrations 18,22 Other compounds Nitrates, fertilisers, iodine-containing products 75,85,90,114 when the thyroid gland itself is not functioning properly, leading to a decreased production of T4 and T3. Secondary hypothyroidism happens when there is a disorder of the anterior pituitary gland, causing impaired production of TSH.…”

“…However, atrial fibrillation can also develop in horses treated with levothyroxine at high doses and in people, over-supplementation is associated with additional cardiovascular disorders including myocardial infarction and congestive heart failure. [69][70][71][72][73][74][75] If a horse has been on prolonged course of thyroid hormone supplementation for vague clinical complaints, gradual weaning over 2-4 weeks is recommended when therapy is to be discontinued.…”

“…Of interest, a recent study demonstrated that performance of Standardbred racehorses was reduced with thyroid hormone supplementation, possibly due to T4‐induced decrease in cardiac function 74 . High T4 concentration, possibly due to excessive T4 supplementation, also increases the risk of adverse effects, including atrial fibrillation and other cardiac arrhythmias 75 . For these reasons, levothyroxine supplementation is not recommended for the treatment of poor performance in horses; rather, horses displaying poor performance should undergo a thorough clinical examination to identify underlying health issues that might be causing suboptimal performance.…”

Anti‐arrhythmic drugs before, during and after transvenous electrical cardioversion of atrial fibrillation in horses: Weighing the benefits and risks

“…These include ACE inhibitors, prednisolone, vitamin C and potassium chloride supplementation (Decloedt et al., 2015). Furosemide treatment and sodium bicarbonate supplementation should be avoided, as well as thyroid hormone supplementation, as this could be associated with an increased risk for atrial arrhythmias (ter Woort et al., 2022).…”

“…Furosemide treatment and sodium bicarbonate supplementation should be avoided, as well as thyroid hormone supplementation, as this could be associated with an increased risk for atrial arrhythmias (ter Woort et al, 2022).…”