Differentiated thyroid carcinoma (DTC)-survivors have an increased risk for cardiovascular mortality yet, the pathophysiological mechanism remains unknown. During early treatment for DTC, thyroid hormone (TH) levels fluctuate from hypothyroidism before ablation therapy to subclinical hyperthyroidism for TSH-suppression. As TH act on the cardiovascular system, fluctuations in TH-levels might have adverse cardiovascular effects. This study aims to investigate cardiac function during early DTC treatment assessed by Cardiac Magnetic Resonance imaging (CMR).

CMR was performed in 18 patients (16 female [89%], median age 47 [IQR 35-59] years) treated for DTC during short-term hypothyroidism and after 20 weeks of subclinical hyperthyroidism. From a subgroup (n=6) an extra CMR was performed before DTC treatment during euthyroidism. Additional cardiovascular- and laboratory parameters were assessed. Data was analysed using a Wilcoxon Singed Rank test.

From hypothyroidism to subclinical hyperthyroidism, heart rate, peak filling rate and peak ejection rate increased (P<.01). Moreover, changes in left ventricular function occurred demonstrated by increased end diastolic volume (EDV), stroke volume (SV), cardiac output (CO), and ejection fraction (P<.05). These changes remained when indexed for body surface area (BSA). Additionally, NT-proBNP-levels were higher during hyperthyroidism (P<.01). Left ventricular end systolic volume, -mass, troponin T, and, galactin-3 did not significantly change. In the subgroup assessed during euthyroidism, a decrease in right ventricular EDV index (indexed for BSA), SV and CO with a decrease in NT-proBNP occurred after the shift to hypothyroidism (P<.05).

The change from hypothyroidism to subclinical hyperthyroidism results in increased systolic left ventricular function indices, increased end diastolic volume and slightly increased NT-proBNP in patients with DTC. Contrarily, from euthyroidism to hypothyroidism, right ventricular function decreases. Therefore, changes in cardiac function may already arise in early DTC treatment.