Thyroid Storm on the Table: How to Navigate the Surgical Nightmare of Hypothyroidism During Cardiac Surgery
"Discover how cardiac surgeons manage high-risk hypothyroid patients undergoing coronary bypass, balancing the risks of thyroid correction and surgical intervention."
Managing hypothyroid patients who need coronary artery bypass grafting (CABG) presents a significant challenge for medical teams. These patients often exhibit a depressed cardiac function, showing unpredictable responses to common inotropic drugs, reduced adrenergic responses, impaired baroreceptor reflexes, and increased systemic vascular resistance (SVR). Though successful management strategies have been reported, the inherent risks are undeniably elevated.
When preparing hypothyroid patients for CABG, several critical factors must be considered. These include an increased sensitivity to depressant medications, a hypodynamic cardiovascular system characterized by reduced heart rate (HR) and cardiac output (CO), slowed drug metabolism, impaired ventilatory responses, hypothermia, blunted baroreceptor reflexes, potential primary adrenal insufficiency, and decreased number and sensitivity of β-receptors. Initiating thyroid hormone therapy preoperatively may trigger angina in patients with ischemic heart disease, potentially leading to myocardial infarction, although such occurrences are rare.
This article explores a case of iatrogenic hypothyroidism (induced by radiotherapy) in a patient with unstable angina. The treating physicians hesitated to correct the thyroid status preoperatively due to concerns about provoking a coronary event. This article details how a grossly hypothyroid patient with unstable angina was managed, focusing on the strategies employed to handle both the thyroid imbalance and the cardiac risks.
Subclinical Hypothyroidism and Cardiac Outcomes
Subclinical hypothyroidism (SCH) is associated with major adverse cardiovascular events, but its relationship with outcomes after cardiac surgery remains uncertain. Research on cardiac postoperative outcomes has yielded conflicting results, and patients are not currently treated for SCH before cardiac surgery. Separately, the relationship between SCH and clinical outcomes after percutaneous coronary intervention (PCI) is also described as uncertain.
Do Not Delay Cardiac Surgery for Euthyroidism
A 2020 review reports higher rates of postoperative atrial fibrillation in patients with hypothyroidism and subclinical hypothyroidism. However, based on the available evidence, its authors conclude that cardiac surgery should not be delayed to achieve euthyroid status. This recommendation reflects the evidence reviewed in that article.
Changing Thyroid Tests Around Cardiac Surgery
A 2018 study categorized patients as hypothyroid when they had increased TSH concentrations of at least 5.5 mIU/L within six months before surgery; it also defined a corrected-hypothyroid group by prior diagnosis or preoperative history. An earlier review noted that thyroid test results can be altered in patients having cardiac procedures, with or without cardiopulmonary bypass (CPB). It identified heart failure, surgical trauma, stress, and polypharmacy during and after the operation as contributing factors.
Case Presentation: Balancing Cardiac and Thyroid Risks
A 58-year-old male with a history of glottic carcinoma, excised five years prior followed by radiotherapy, was scheduled for CABG due to triple vessel disease and unstable angina. Post-radiotherapy, he developed iatrogenic hypothyroidism but was not consistent with his thyroxine medication. Preoperative findings indicated a TSH level of 93 µIU/ml (normal range: 0.45 - 4.5 µIU/ml), Free T3 at 0.02 pg/mL (normal range: 2.3-4.2 pg/mL), and Free T4 at 0.04 ng/L (normal range: 0.8 - 1.8 ng/L).
- Preoperative Management: The patient was maintained on thyroxine 100 µg, isosorbide, atorvastatin, and aspirin.
- Steroid Supplementation: Perioperative steroid supplementation was initiated to mitigate potential adrenal insufficiency associated with hypothyroidism.
- Airway Management: Awake fiberoptic intubation was performed nasally with minimal sedation (fentanyl 100 µg and midazolam 2 mg). Tablet thyroxine 100 µg was administered post-induction via a Ryle’s tube.
Recent Reviews Focus on SCH After CABG
A 2023 report on subclinical hypothyroidism (SCH) notes that its association with major adverse cardiovascular events is recognized, while research on postoperative cardiac outcomes has produced conflicting results. It also reports that patients are not currently treated for SCH before cardiac surgery. A 2024 systematic review and meta-analysis focused on associations between SCH and long-term cardiovascular outcomes after coronary artery bypass grafting (CABG).
Limits of the Evidence
The systematic review and meta-analysis identifies limitations inherent to study-level analyses based on retrospective observational series. These include possible methodological heterogeneity among included studies and residual confounding. The authors also flag ecological fallacy in meta-regression and possible treatment-allocation bias, since surgeons may alter surgical decisions based on patients’ laboratory data.
Different Findings Across Thyroid Conditions
A case report on thyroid storm after coronary artery bypass surgery cites an incidence of 0.20–0.76 per 100,000 persons per year and 4.8–5.6 per 100,000 hospitalized patients per year. In an off-pump CABG study, long-term mortality at a median 30-month follow-up was 9.6% in the low-T3 group, 11.3% in the SCH group, and 2.4% in the euthyroid group (p < 0.001). By contrast, another study concluded that hypothyroidism did not affect the frequency of complications or outcomes after cardiac surgery and that achieving euthyroid status beforehand was unnecessary.
Key Takeaways
Based on this experience, it is preferable to optimize a patient’s thyroid status with preoperative thyroxine supplementation, aiming for a near-normal or mildly hypothyroid state, rather than operating on a grossly hypothyroid patient. Levosimendan shows promise as an inotrope to counteract the adverse effects of reduced thyroid hormone levels, particularly in improving cardiac contractility and reducing systemic vascular resistance, especially since it operates independently of β-adrenergic receptors. Further research is needed to fully understand its effectiveness in these critical situations.
Reported Risks After Cardiac Surgery
A February 2024 report states that patients with subclinical hypothyroidism have higher operative mortality after cardiac surgery. It also reports a longer hospital length of stay and a higher rate of renal complications in this group. These are the outcomes reported by the source.
Testing Whether Thyroid Normalization Helps
A July 2026 report identifies interventional trials as a future research direction. Such trials could assess whether normalizing thyroid hormone levels before surgery improves short-term surgical recovery. The proposed research would also examine possible effects on long-term cardiovascular prognosis in hypothyroid patients undergoing CABG.
Thyroid Function in Cardiac and Vascular Surgery
A 2025 study aims to clarify the relationship between thyroid function and surgical prognosis in patients undergoing cardiac and major vascular surgeries. A separate 2026 report describes thyroid dysfunction as associated with adverse postoperative outcomes, while noting that its effects in patients undergoing CABG are little known. That report sets out to evaluate CABG incidence among patients with hypothyroidism receiving thyroid hormone replacement therapy and assess short- and long-term outcomes.
Unsettled Effects on Patients
A 2022 cohort-study source describes hypothyroidism as potentially affecting metabolic, cardiovascular, respiratory, and immune systems, but says there is no confirmed conclusion about its effect on cardiovascular surgery. The same source summarizes a study of 222 euthyroid and 36 SCH patients who underwent CABG. Over a mean follow-up of 8.2 ± 4.1 years, that study reviewed all-cause and cardiovascular-related mortality and cardiovascular events.