Does Synthroid (levothyroxine) have vasoactive properties in cardiac surgeries?

Synthroid (Levothyroxine) Does Not Have Significant Vasoactive Properties in Cardiac Surgeries

Synthroid (levothyroxine) is not considered a vasoactive agent and is not used for hemodynamic support during cardiac surgeries. While thyroid hormones do have cardiovascular effects, levothyroxine is not utilized as a vasoactive medication in the perioperative cardiac surgery setting.

Cardiovascular Effects of Levothyroxine

• Levothyroxine can cause cardiovascular effects primarily when used in excessive doses, resulting in symptoms of hyperthyroidism including palpitations, tachycardia, arrhythmias, increased pulse and blood pressure, heart failure, angina, myocardial infarction, and cardiac arrest 1
• The FDA label for levothyroxine specifically warns about monitoring for cardiac arrhythmias during surgical procedures in patients with coronary artery disease who are receiving suppressive levothyroxine therapy 1
• Patients receiving concomitant levothyroxine and sympathomimetic agents should be monitored for signs and symptoms of coronary insufficiency 1

Vasoactive Medications in Cardiac Surgery

• Current guidelines for cardiopulmonary bypass in adult cardiac surgery recommend specific vasoactive and inotropic agents for hemodynamic support, which do not include levothyroxine 2
• The recommended first-line treatments for hemodynamic instability during cardiac surgery are traditional positive inotropic and/or vasopressor agents such as dobutamine, adrenaline, noradrenaline, phosphodiesterase III inhibitors, and calcium sensitizers 2
• Phosphodiesterase inhibitors are specifically recommended to increase weaning success from cardiopulmonary bypass 2

Thyroid Hormone in Cardiac Surgery Context

• While there has been some research on triiodothyronine (T3) administration in cardiac surgery, particularly for patients difficult to wean from cardiopulmonary bypass, levothyroxine (T4) is not routinely used for this purpose 3
• Some data indicate that patients with acute and chronic cardiovascular disorders and those undergoing cardiac surgery may have altered peripheral thyroid hormone metabolism, but this does not establish levothyroxine as a vasoactive agent 4
• Anecdotal experience suggests T3 (not levothyroxine/T4) may help in weaning patients from cardiopulmonary bypass who are unable to be weaned despite maximal inotropic support, but rigorous clinical trials have failed to support routine use 3

Hemodynamic Effects of Levothyroxine

• In critically ill hypothyroid patients, high-dose levothyroxine loading has been shown to increase cardiac index, but this is not the same as having direct vasoactive properties 5
• The cardiovascular effects of levothyroxine are primarily related to its hormonal action rather than direct vasoactive properties, and these effects develop gradually rather than acutely 4, 6
• Hypothyroid patients undergoing surgery may experience more intraoperative hypotension and postoperative complications, but levothyroxine is used to treat the underlying hypothyroidism rather than as a vasoactive agent 7

Clinical Implications

• When managing hemodynamic instability during cardiac surgery, clinicians should rely on established vasoactive agents as recommended in current guidelines 2
• For patients on levothyroxine therapy undergoing cardiac surgery, monitoring for potential cardiac effects is important, but levothyroxine itself is not used for hemodynamic support 1
• If cardiac symptoms develop or worsen in patients on levothyroxine, the recommendation is to reduce the dose or withhold for one week and restart at a lower dose, rather than using it for vasoactive purposes 1

In conclusion, while thyroid hormones do affect cardiovascular function, Synthroid (levothyroxine) is not considered a vasoactive agent and is not used for hemodynamic support during cardiac surgeries. The established vasoactive medications for cardiac surgery include catecholamines, phosphodiesterase inhibitors, and calcium sensitizers.