Cardiovascular effects of intravenous triiodothyronine in patients undergoing coronary artery bypass surgery

A prospective, randomised and double blind folded study was performed to evaluate whether perioperative triiodothyronine administration had any effect on cardiovascular performance in patients undergoing elective coronary artery bypass surgery. 60 patients were enrolled in the study, 30 in each group. Patients in Group A received intravenous bolus of 0.8 mcg.kg of triiodothyronine (T<sub>3</sub>) (Thyrotardin-inject. N Hennig Berlin) when the aortic cross clamp was removed, followed by an infusion of 0.113 mcg./kg./hr of hormone for six hours. Patients in Group B received placebo. Clinical and hemodynamic parameters were serially measured. Although the mean postoperatif cardiac index was slightly higher in the triidothyronine group (2.75±0.52, 2.63±0.60) this didn't reach a statistically significant level (p=n.s.). However the difference in systemic vascular resistance was significantly lower in T<sub>3</sub> group (1040±220, 1350±420 dyn.sc.cm.) (p<0.001). Serum T<sub>3</sub> levels dropped significantly in group B patients after cardiopulmonary bypass, 6 and 12 hours postoperativly (p<0.001), while raised significantly in group A patients (p<0.001). No significant difference was detected between two groups in terms of arrhythmia incidence, need for inotropic support, intensive care unit stay, mortality and morbidity. Perioperative administration of triiodothyronine slightly increased Cardiac index, significantly decreased systemic vascular resistance, but had no effect on outcome. Although its use is safe, routine use of intravenous T<sub>3</sub> can not be recommended at this time. Thyroid hormone metabolism has been shown to be altered during cardiopulmonary bypass, thereby resulting in reductions of serum thyroid hormone concentrations. It has been suggested that this reduction may contribute to hemodynamic instability during the early postoperative period. Whether reduced serum T<sub>3</sub> levels contribute to ventricular dysfunction after open heart surgery or intravenous T<sub>3</sub> has acute inotropic effects in this setting is unknown. In a number of clinical studies, patients undergoing coronary bypass operations who received intravenous T<sub>3</sub> had an increase in cardiac output, but no significant outcome was observed. Despite this, some groups have advocated its use in certain areas such as prophylaxis of atrial fibrillation or as a rescue agent to improve cardiac output in patients who are difficult to wean from cardiopulmonary bypass (CPB).