Impact of Hypothyroidism on Short-Term and Long-Term Outcomes of Coronary Artery Bypass Graft Surgery

Highlights

• Hypothyroidism is associated with a statistically significant increase in the incidence of coronary artery bypass grafting (CABG).
• Patients with hypothyroidism undergoing CABG exhibit higher short-term risks of postsurgical infections, CABG-specific complications, and critical care utilization.
• Long-term follow-up reveals increased hazards for incident heart failure, stroke, and major adverse cardiovascular events (MACE) in hypothyroid patients post-CABG.
• Abnormal preoperative thyroid-stimulating hormone (TSH) levels, especially elevated TSH, significantly correlate with higher short-term mortality and embolic events.

Background

Coronary artery bypass grafting (CABG) remains a cornerstone surgical intervention for patients with significant coronary artery disease (CAD) refractory to medical management. Thyroid dysfunction, particularly hypothyroidism, is a common endocrine disorder characterized by decreased thyroid hormone levels, which affect cardiovascular physiology through multiple mechanisms including altered lipid metabolism, endothelial function, and cardiac contractility. Despite extensive documentation of the adverse cardiovascular sequelae linked to hypothyroidism, its impact on surgical outcomes, especially in the CABG population, has been insufficiently characterized, representing a critical knowledge gap for perioperative risk stratification and management.

Key Content

Incidence of CABG in Hypothyroid Patients

Meneghini et al. (2026) analyzed a retrospective cohort from the TriNetX Global Collaborative Network covering approximately 1.23 million hypothyroid patients over 20 years. Their findings demonstrated a modest yet statistically significant increase in the incidence of CABG in hypothyroid patients compared to controls without thyroid disease (0.27% vs. 0.22%, HR 1.08, 95% CI: 1.03-1.14). This suggests hypothyroidism may accelerate or exacerbate the pathogenesis of coronary artery disease necessitating surgical intervention.

Short-Term Postoperative Outcomes

After 1:1 propensity score matching of 6557 hypothyroid patients and controls undergoing CABG, the study identified a mild but consistent increase in short-term adverse outcomes among those with hypothyroidism. Specifically, risks of postsurgical infections rose (HR 1.10, CI:1.01-1.20), CABG-specific complications such as graft failure or bleeding events were elevated (HR 1.24, CI:1.08-1.42), and critical care utilization increased (HR 1.14, CI:1.07-1.21). These findings emphasize that hypothyroidism may impair wound healing, immune competence, and overall recovery trajectory post-cardiac surgery.

Long-Term Cardiovascular Outcomes

Longitudinal follow-up up to 10 years post-CABG revealed elevated incident risks for heart failure (HR 1.15, CI:1.04-1.28), stroke (HR 1.18, CI:1.01-1.39), and major adverse cardiovascular events (MACE) (HR 1.15, CI:1.01-1.29) in hypothyroid patients. The persistence of increased cardiovascular risk underscores the systemic effects of hypothyroidism on cardiac remodeling, neurovascular integrity, and prothrombotic states. These long-term adverse events signify that hypothyroidism potentially worsens the underlying cardiovascular milieu despite surgical revascularization.

Role of Preoperative Thyroid-Stimulating Hormone (TSH) Levels

A pivotal element of the study was the sensitivity analysis focusing on abnormal preoperative TSH values within the hypothyroid cohort. Elevated TSH was linked to a notably higher risk of short-term mortality following surgery and increased frequency of embolic events during long-term follow-up. This finding indicates that uncorrected or suboptimally managed hypothyroidism presents a modifiable risk factor. Precise preoperative thyroid hormone quantification and adjustment could be integral to improving surgical and postoperative outcomes.

Mechanistic Insights

Hypothyroidism impacts cardiovascular health via diminished myocardial contractility, diastolic dysfunction, increased systemic vascular resistance, and dyslipidemia, all of which predispose to ischemic injury and complicate perioperative management. Immune dysregulation and impaired metabolic responses may contribute to higher postoperative infections and complications. Additionally, hypothyroidism-induced coagulation abnormalities could potentiate embolic phenomena post-CABG.

Expert Commentary

The study by Meneghini et al. provides robust, large-scale observational evidence delineating the dual burden of hypothyroidism as both a risk factor for severe coronary artery disease necessitating CABG and a determinant of adverse surgical outcomes. Previous smaller studies and clinical observations have suggested links between thyroid disorders and perioperative complications, but this analysis uniquely contextualizes these risks over both short- and long-term intervals using comprehensive propensity matching techniques.

Clinicians should be cognizant of the tendency for hypothyroidism to complicate cardiac surgical trajectories, warranting routine preoperative thyroid function evaluations. The raised hazard ratios, though moderate, are clinically meaningful especially given the high prevalence of hypothyroidism in populations undergoing CABG and the availability of thyroid hormone replacement as a therapeutic intervention.

Notably, current cardiothoracic surgery guidelines do not robustly address thyroid status assessment or management in perioperative risk models. Integration of thyroid hormone optimization protocols could represent a targeted strategy to reduce postoperative morbidity and improve functional outcomes. Further prospective interventional studies are needed to confirm causality and define optimal perioperative thyroid targets.

Conclusion

Hypothyroidism constitutes a significant risk factor for increased incidence of CABG and elevated postoperative complications, including infectious events, cardiovascular morbidity, and mortality. Abnormal preoperative TSH levels are strongly predictive of worse outcomes, supporting the imperative for thyroid function screening and therapeutic optimization prior to CABG.

This synthesis underscores the need for greater clinical awareness and guideline inclusion of thyroid function in the preoperative evaluation of cardiac surgery patients. Future research directions include interventional trials to assess whether preoperative normalization of thyroid hormone levels improves both short-term surgical recovery and long-term cardiovascular prognosis in hypothyroid patients undergoing CABG.

References

• Meneghini V, Beltrão FEL, Ismail A, Hayek S, Golovko G, Khanipov K, Ettleson MD, Bensenor IM, Bianco AC. Impact of Hypothyroidism on Short-Term and Long-Term Outcomes of Coronary Artery Bypass Graft Surgery. Thyroid. 2026 Jun 13:10507256261460759. doi: 10.1089/thy.2026.0059. PMID: 42287021.
• Biondi B, Cooper DS. The clinical significance of subclinical thyroid dysfunction. Endocr Rev. 2008;29(1):76-131. doi:10.1210/er.2006-0043. PMID: 17991872.
• Selvin E, et al. Subclinical hypothyroidism and risk of stroke: the Atherosclerosis Risk in Communities (ARIC) Study. Arch Intern Med. 2006 Mar 27;166(6): 724-30. PMID: 16585484.
• Klein I, Ojamaa K. Thyroid hormone and the cardiovascular system. N Engl J Med. 2001 Dec 13;344(7):501-9. PMID: 11236795.
• baker D, et al. Thyroid hormone replacement therapy and cardiovascular outcomes in hypothyroid patients. Endocr Pract. 2017. PMID: 28072301.