TSH variability and atrial fibrillation in patients with DTC: A regional cohort study.

[BACKGROUND] The study aimed to analyze thyroid-stimulating hormone (TSH) levels quantitatively and investigate their potential correlation with the risk of incident atrial fibrillation (AF) in differentiated thyroid cancer (DTC) patients.

[METHODS] DTC cases diagnosed between 1995 and 2015 in Stockholm, Sweden, were identified from the Swedish Cancer Registry. Medical records were scrutinized, and follow-up began 9 months post-surgery with tracking data until the earliest AF record, censoring, or 31 August 2022. TSH values were classified as unsuppressed (TSH > 0.5 mE/L), mildly suppressed (TSH 0.1-0.5 mE/L), or suppressed (TSH < 0.1 mE/L), with graphical analysis spanning up to a 10-year follow-up period. In addition, a nested case-control study assessed the impact of TSH category on incident AF. Additional data on cardiovascular risk factors were gathered.

[RESULTS] Among 608 patients, approximately 78% maintained suppressed TSH levels for over half of their follow-up time. Notably, there was a decrease in the proportion of patients receiving long-term TSH suppression after 2013. Among 39 newly diagnosed AF cases, most were in the suppressed TSH category. Moreover, about half of these new AF patients had established cardiovascular risk factors prior to DTC diagnosis.

[CONCLUSION] DTC patients generally adhered to TSH suppression guidelines, with a decline observed in the proportion of suppressed TSH values following the adoption of individualized treatment in 2013. The study could not establish a clear link between TSH suppression and the risk of incident AF, highlighting the need for further investigation.