Preoperative hypothyroidism is associated with increased morbidity and mortality following cardiac surgery: a pooled analysis

Introduction The association between hypothyroidism and prognosis following cardiac surgery remains poorly understood. This study evaluated the association of preoperative hypothyroidism with postoperative complications and mortality. Methods PubMed, Embase, Cochrane Library, Web of Science, MEDLINE, and Scopus were searched from inception to December 17, 2025, to identify eligible studies. Pooled odds ratios and 95% confidence intervals were calculated to assess the associations between hypothyroidism and postoperative outcomes. Subgroup and leave-one-out sensitivity analyses explored heterogeneity and assessed the stability of the findings. Results A total of 40,968 patients were enrolled in 22 studies for pooled analysis. For postoperative complications, more patients in the hypothyroid group developed acute kidney injury (OR = 2.61, 95% CI = 1.85 to 3.69, P = 0.00, I 2 = 0.00%), myocardial infarction (OR = 1.66, 95% CI = 1.23 to 2.23, P = 0.00, I 2 = 11.94%) and major adverse cardiovascular events (OR = 1.59, 95% CI = 1.45 to 1.74, P = 0.00, I 2 = 0.00%). However, regarding atrial fibrillation (OR = 1.24, 95% CI = 0.89 to 1.71, P = 0.20, I 2 = 71.05%), heart failure (OR = 1.46, 95% CI = 0.92 to 2.33, P = 0.11, I 2 = 0.00%), and stroke (OR = 1.36, 95% CI = 0.93 to 2.00, P = 0.11, I 2 = 0.00%), no statistically significant differences were observed between the two groups. As for mortality, both in-hospital mortality (OR = 1.70, 95% CI = 1.03 to 2.79, P = 0.04, I 2 = 0.00%) and long-term mortality (OR = 1.70, 95% CI = 1.29 to 2.25, P = 0.00, I 2 = 62.52%) were higher in the hypothyroid group. In additional analyses restricted to adjusted effect estimates, the association with heart failure reached statistical significance (aOR = 1.53, 95% CI = 1.14 to 2.04, P = 0.00, I 2 = 0.00%), whereas the associations with myocardial infarction and long-term mortality were not statistically significant. Conclusion This study demonstrates that preoperative hypothyroidism was associated with several adverse outcomes following cardiac surgery, providing supportive evidence that surgeons should assess patients’ thyroid function and initiate appropriate interventions preoperatively.