From the Guidelines

Yes, thyroid cancers can cause atrial fibrillation (afib) indirectly through hyperthyroidism.

Hyperthyroidism, which can be caused by thyroid cancers, is a known risk factor for atrial fibrillation, with a threefold increased risk of developing afib 1.
The relationship between hyperthyroidism and cardiovascular abnormalities, including afib, is well established, with thyroid hormones directly affecting the factors that determine oxygen consumption of the myocardium 1.
Studies have shown that patients with subclinical hyperthyroidism, characterized by low serum TSH levels, also have an increased risk of afib, particularly when TSH values are lower than 0.1 mIU/L 1.

Thyroid hormones can cause coronary artery spasm and directly affect the myocardium, leading to the development of chronic stable angina and increasing the risk of afib 1.
Management of afib in patients with hyperthyroidism typically involves the use of nonselective β-blockers, such as propranolol, or alternative treatments like diltiazem, verapamil, or ivabradine if β-blockers are contraindicated 1.
Correcting metabolic defects, including hyperthyroidism, may help prevent the onset of afib, particularly in the elderly 1.

From the Research

Studies have investigated the relationship between thyroid cancer and atrial fibrillation (AF), with some suggesting a possible link between the two conditions 2, 3, 4.
A meta-analysis found that patients with differentiated thyroid cancer (DTC) are at a high risk for developing AF, with an incidence rate ratio of 1.54 (95% CI, 1.44 to 1.65) compared to healthy controls 2.
Another study found that DTC patients have a 2.25-fold increased risk of AF compared to controls, with a higher cumulative radioiodine dose slightly increasing AF risk 3.
A cross-sectional study found a prevalence of AF of 10.3% in patients with thyroid cancer on TSH suppressive therapy, with the rate of AF in patients aged 60 years and over being higher than in published data for the general population 4.

A study examining the association between AF and various cancer subtypes found that thyroid cancer was not significantly associated with AF at any age 5.
However, other studies have suggested a link between thyroid cancer and cardiovascular disease risk, including AF 6.
A nationwide observational study found that thyroid cancer survivors have a substantial coronary heart disease risk, but the association between thyroid cancer and AF risk was insignificant 6.

The exact mechanisms underlying the potential link between thyroid cancer and AF are unclear, but may involve long-term cardiovascular toxicity associated with treatment, such as TSH suppression therapy 2, 3, 4.
Further research is needed to fully understand the relationship between thyroid cancer and AF, including the role of treatment and other potential risk factors 2, 3, 4, 6.