Younger Age, Female Gender Linked to Incident Hyperthyroidism Among AF Patients

Younger age, female gender, history of congestive heart failure, and non-end stage kidney disease are associated with the development of hyperthyroidism among patients with atrial fibrillation, according to study findings published in the Journal of Clinical Endocrinology & Metabolism.

Although previous studies have shown a link between atrial fibrillation and increased hyperthyroidism risk, the risk factors remain unclear. Researchers at National Taiwan University Hospital conducted a retrospective, cross-sectional cohort study from January 2010 to December 2016 to determine if atrial fibrillation could predict hyperthyroidism risk.

Participants included patients aged 18 years or older without hyperthyroidism at time of atrial fibrillation diagnosis. Hyperthyroidism was characterized by serum thyroid stimulating hormone, free thyroxine, and total triiodothyronine levels. The researchers confirmed the diagnosis of hyperthyroidism if patients had at least 2 outpatient visits or 1 inpatient visit. 

The researchers collected demographic data and baseline characteristics, including hypertension, diabetes, coronary artery disease, end-stage kidney disease, and stroke. The CHADS2 and CHA2DS2-VASc scores were used for stroke risk assessment. The primary endpoint was newly diagnosed hyperthyroidism within the follow-up period. 

The study included a total of 8552 patients with atrial fibrillation, of whom 647 were diagnosed with hyperthyroidism during follow-up (median, 48.8 months; SD, 35.3 months).

Compared with patients who did not develop hyperthyroidism, those who developed hyperthyroidism were younger on average (67.4 years vs 72.3 years; P =.003) and more likely to be women (64% vs 47%).   

Patients with hyperthyroidism, compared with those without hyperthyroidism, also had lower rates of comorbidities, including:

• Diabetes (26% vs 29%; P =.121);
• Hypertension (51% vs 58%; P <.001);
• Coronary artery disease (17% vs 25%; P <.001);
• Stroke (16% vs 22%, P <.001); and,
• End-stage kidney disease (6% vs 10%; P =.001)

Higher baseline CHA2DS2-VASc scores were associated with a lower incidence of hyperthyroidism during the study period (P <.001). After the researchers used baseline high sensitivity thyroid stimulating hormone levels to adjust for the potential bias of subclinical hyperthyroidism, this relationship remained consistent (P <.001). 

The researchers identified several independent predictors of hyperthyroidism in patients with atrial fibrillation, including:

• Younger age (hazard [HR], 0.657; 95% CI, 0.507-0.852; P =.002);
• Female gender (HR, 2.107; 95% CI, 1.709-2.596; P < .001);
• History of congestive heart failure (HR, 1.623; 95% CI, 1.129-2.333; P =.009);
• Hypertension (HR, 1.453; 95% CI, 1.021-2.067; P =.038);
• Diabetes (HR, 1.502; 95% CI, 1.057-2.136; P =.023);
• Non-end stage kidney disease (HR, 0.581; 95% CI, 0.377-0.895; P =.014); and,
• Lower CHADS2 score (HR, 0.741; 95% CI, 0.573-0.959; P =.023).

Study limitations include the lack of hyperthyroidism medication records, a possible underestimation of hyperthyroidism incidence due to varying follow-up times, and the small number of hyperthyroidism cases.

“These findings may provide new insight into the pathogenesis of hyperthyroidism in these specific groups and future therapeutic strategies,” the study researchers concluded. “However, further research is needed to confirm our findings and promote more intensive screening, as well as to explore the underlying mechanism.”

This article originally appeared on Endocrinology Advisor