Cardiovascular Morbidity and Mortality After Treatment of Hyperthyroidism with Either Radioactive Iodine or Thyroidectomy

Background: Hyperthyroid patients remain at an increased risk of cardiovascular diseases (CVDs) after restoring euthyroidism. The impact of the different treatment modalities of hyperthyroidism on future CVD risk remains unclear. The aims of this study were to assess cardiovascular morbidity and mortality in hyperthyroidism before and after treatment, and to compare the effects of two different treatment modalities: radioactive iodine (RAI) and thyroid surgery. Methods: A comparative cohort study was conducted among 6148 hyperthyroid patients treated with either RAI or thyroidectomy and 18,432 age- and sex-matched controls. First, hospitalizations due to CVDs prior to the treatment were analyzed. Second, the hazard ratios (HR) for any new hospitalization and mortality due to CVDs after treatment were estimated among all the hyperthyroid patients compared to the age- and sex-matched controls and also in the RAI-treated patients compared to the thyroidectomy-treated patients. The results were adjusted for prevalent CVDs at the time of treatment. Results: Before treatment for hyperthyroidism, hospitalizations due to all CVDs were more common in the hyperthyroid patients compared to the controls (odds ratio=1.61 [confidence interval (CI) 1.49-1.73]). During the post-treatment follow-up, hospitalizations due to CVDs remained more frequent among the patients (HR=1.15 [CI 1.09-1.21]), but there was no difference in CVD mortality (HR=0.93 [CI 0.84-1.03]). Compared to the patients treated with thyroidectomy, the RAI-treated patients had a higher risk of hospitalization due to all CVDs (HR=1.17), atrial fibrillation (HR=1.28), as well as a higher CVD mortality rate (HR=2.56). Yet, treatment with RAI resulting in hypothyroidism was not associated with increased CVD morbidity compared to thyroidectomy. Conclusions: Hyperthyroidism increases the risk of CVD-related hospitalization, and the risk is sustained for up to two decades after treatment with RAI or surgery. Hyperthyroid patients treated with RAI remain at a higher CVD risk compared to patients treated with thyroidectomy. Hypothyroidism during follow-up, however, predicts better cardiovascular outcomes.