Subclinical Hypothyroidism and Clinical Outcomes after Cardiac Surgery – A Systematic Review and Meta-analysis

Objectives Subclinical hypothyroidism (SCH) is associated with major adverse cardiovascular events (MACE). Despite the recognized negative impact of SCH on cardiovascular health, research on cardiac post-operative outcomes with SCH has yielded conflicting results and patients are not currently treated for SCH before cardiac surgery procedures. Methods We performed a study-level meta-analysis about the impact of SCH on patients undergoing non-urgent cardiac surgery including coronary artery bypass graft, valve and aortic surgery. The primary outcome was operative mortality. Secondary outcomes were hospital length of stay (LOS), intensive care unit (ICU) stay, postoperative atrial fibrillation (POAF), intra-aortic balloon pump (IABP) use, renal complications, and long-term all-cause mortality. Results Seven observational studies (3445 patients - 851 [24.7%] diagnosed with SCH and 2594 [75.3%] euthyroid patients) were identified. Compared to euthyroid patients, those with SCH had higher rates of operative mortality (OR: 2.57, 95% CI, 1.09-6.04, p=0.03), prolonged hospital LOS (SMD: 0.32, 95% CI, 0.02 to 0.62, p=0.04), higher rates of renal complications (OR: 2.53, 95% CI, 1.74-3.69, p<0.0001), but no significant differences in ICU stay, POAF or IABP use. At mean follow-up of 49.3 months, the presence of SCH was associated with higher rates of all-cause mortality (IRR: 1.82, 95% CI, 1.18-2.83, p=0.02). Conclusion Patients with SCH have higher operative mortality, prolonged hospital LOS and renal complications after cardiac surgery. Achieving and maintaining a euthyroid state prior to and after cardiac surgery procedures might improve outcomes.