Plain language summary
Thyroid dysfunction, particularly in its subclinical forms, has been linked to various cardiovascular issues, including atrial fibrillation (AF). Subclinical thyroid dysfunction is characterized by abnormal thyroid-stimulating hormone (TSH) levels while free thyroid hormone levels remain normal. The primary aim of this study was to assess the association between subclinical hyperthyroidism and hypothyroidism and the risk of incident atrial fibrillation. This research is a systematic review and meta-analysis that included cohort studies, focusing on the relationship between subclinical thyroid dysfunction and incident AF. Results showed that both subclinical hyperthyroidism and subclinical hypothyroidism increased the risk of incident AF by 99% and 19%, respectively. Subclinical hypothyroidism was not found to significantly increase the risk of incident post-operative AF; however, there was considerable heterogeneity and variation in surgical procedures. Authors concluded their findings suggest that both subclinical hyperthyroidism and hypothyroidism are linked to an increased risk of incident atrial fibrillation. However, the quality of the evidence is considered low, indicating a need for further research.
Abstract
BACKGROUND Thyroid hormones act on the cardiovascular system directly by modulating its function and indirectly by transcriptional regulation of gene expression in the heart and the vasculature. Studies have shown associations between overt and subclinical thyroid disorders and cardiovascular outcomes. The aim of this study was to perform a systematic review and meta-analysis to assess the potential relationships between subclinical hyper- and hypothyroidism and risk of atrial fibrillation (AF), and post-operative AF. METHODS MEDLINE and Scopus databases were searched from inception to 18th February 2023 for randomised controlled trials, case-control studies, and cohort studies which assessed the relationship between subclinical thyroid dysfunction and incident AF events. Risk of bias and the quality of evidence were assessed using the RoBANS tool and GRADE approach, respectively. Meta-analysis was conducted in Review Manager 5.4 using the Mantel-Haenszel statistical method and a random-effects model. Data are presented as risk ratios with 95% confidence intervals. Statistical heterogeneity amongst studies was assessed by the chi-squared (χ2) test and I2 statistic. p≤0.05 were considered significant. RESULTS A total of 6467 records were identified, of which 10 cohort studies met the inclusion criteria. Both subclinical hyperthyroidism and subclinical hypothyroidism were associated with an increased risk of incident AF (risk ratio (RR), 1.99; 95% confidence interval (CI), 1.43-2.77; n = 5 studies; p<0.0001 and RR, 1.19; CI, 1.03-1.39; n = 7 studies; p = 0.02, respectively). Subgroup analysis for post-operative AF revealed marked heterogeneity between studies (I2 = 84%) and association with subclinical hypothyroidism was not significant (RR, 1.41; CI, 0.89-2.22; n = 3 studies; p = 0.15). CONCLUSIONS The current evidence suggests that both subclinical hyperthyroidism and subclinical hypothyroidism are associated with increased risk of incident AF. Further investigation is required to determine potential causal links that would guide future clinical practice.
Methodological quality
Jadad score
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Allocation concealment
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