Biochemically diagnosed hypothyroidism and postoperative complications after cardiac surgery: a retrospective cohort analysis.

PURPOSE: To determine whether hypothyroidism is associated with cardiovascular complications and surgical wound infections after cardiac surgery.

METHODS: Patients were categorized as: (1) hypothyroid [patients with increased TSH concentrations (≧ 5.5 mIU/L) within 6 months prior to surgery]; (2) corrected hypothyroid [diagnosis of hypothyroidism any time before surgery or on preoperative thyroid supplementation and normal TSH concentration (0.4 [Formula: see text] TSH [Formula: see text] 5.5 mIU/L]; and (3) euthyroid [no hypothyroid diagnosis and not on preoperative thyroid supplementation and normal TSH concentrations (0.4-5.5 mIU/L)]. We conducted pairwise comparisons among the three groups using inverse probability of treatment weighting. We compared the groups on postoperative myocardial infarction, cardiac arrest, atrial fibrillation, and a composite of surgical wound infections and postoperative vasopressor use using multivariable logistic regression models. We compared the groups on ICU and hospital length of stay using Cox proportional hazards regression.

RESULTS: Hypothyroidism was associated with a lower risk of atrial fibrillation than euthyroidism, with an estimated relative risk (99.4% CI) of 0.71 (0.56, 0.89); P < 0.001. However, none of the other pairwise comparisons on myocardial infarction, cardiac arrest, and atrial fibrillation were significant. Corrected hypothyroid patients were slightly more likely to be discharged from hospital at any given time than euthyroid patients (hazard ratios (99.6% CI), 1.18 (1.07, 1.30); P < 0.001), but no other pairwise comparisons for secondary outcomes were significant.

CONCLUSIONS: Hypothyroidism was associated with lower risk of atrial fibrillation than euthyroidism, and corrected hypothyroidism was associated with a shorter length of stay than euthyroidism.