Electrocardiographic and scintigraphic evaluation of patients with subclinical hyperthyroidism during workout

Abstract

Subclinical hyperthyroidism (sHT) was found to be associated with elevated heart rate, blood pressure and increased risk of extrasystoles. However, the full clinical relevance of morphological and functional implications of sHT on the cardiovascular system is still a matter of debate. The aim of the study was to prospectively assess the influence of endogenous sHT on exercise capacity and cardiac function during workout with the use of exercise electrocardiography (ExECG) and perfusion scintigraphy. The studied group consisted of 44 consecutively recruited patients diagnosed with sHT. In all patients, ExECG, followed by post-exercise myocardial perfusion imaging, was performed. Both ExECG and scintigraphy were performed twice—in the state of sHT and after euthyroidism was restored. An average time period of exercise test was significantly longer in the state of euthyroidism than in sHT. An average oxygen consumption during exercise test was also higher after euthyroidism was achieved when compared to sHT. The end-diastolic and end-systolic volume indexes, stroke volume index and cardiac index were significantly larger in patients with sHT if compared values achieved after euthyroidism restoration. Stroke volume index was negatively correlated with TSH, and positively with free thyroid hormones values in the state of sHT, before euthyroidism was achieved. Cardiac index was positively correlated with free thyroid hormones levels. The obtained results indicate worse physical capacity in subjects with sHT and improvement of several parameters assessed during ExECG and perfusion scintiscan after therapy. Observed changes might reflect the mechanism of the deleterious effect exerted by sHT on the heart.

Thyroid Hormones within the Normal Range and Cardiac Function in the General Population: The EPIPorto Study

“…Our results suggest that, even within the normal range, variations of thyroid function have a relevant effect on heart rate and blood pressure, which has also been suggested by previous studies [17,42]. Overt and subclinical hyperthyroidism has also been associated with an increased risk of cardiac arrhythmias [43][44][45] and with volume overload [46]. In the Rotterdam Study, Chaker et al [47,48] found that increasing thyroid function was associated with a higher risk of atrial fibrillation in euthyroid participants and a higher risk of sudden cardiac death.…”

Long-term cardiovascular and cerebrovascular morbidity in Israeli thyroid cancer survivors

“…However, others have reported the contributions of the therapeutic components. A poorer cardiovascular profile has been reported among individuals with subclinical hyperthyroidism not associated with TC (24, 25, 26, 27, 28, 29, 30, 31). However, a pooled analysis of four prospective cohort studies failed to demonstrate any association between subclinical hyperthyroidism and stroke (32).…”

Long-term all-cause mortality and its association with cardiovascular risk factors in thyroid cancer survivors: an Israeli population-based study

“…In the absence of data on thyroid hormone treatment, we do not know the degree to which subclinical hyperthyroidism was achieved in the TC survivors, or the proportion of individuals in the TC group that may have had endogenous subclinical hyperthyroidism. However, subclinical hyperthyroidism not in the setting of TC has been shown to be associated with atrial fibrillation [ 32 , 33 ] worse physical capacity [ 34 ], increased risk of heart failure, and cardiovascular morbidity [ 33 , 35 ]. Moreover, endogenous subclinical hyperthyroidism was associated with increased risks of total and cardiovascular mortality in a pooled analysis from 10 cohorts of individuals not treated with thyroxine [ 32 ].…”