BACKGROUND: Thyroid hormone has many effects on the cardiovascular system. 
During and after cardiopulmonary bypass, serum triiodothyronine concentrations 
decline transiently, which may contribute to postoperative hemodynamic 
dysfunction. We investigated whether the perioperative administration of 
triiodothyronine (liothyronine sodium) enhances cardiovascular performance in 
high-risk patients undergoing coronary-artery bypass surgery.
METHODS: We administered triiodothyronine or placebo to 142 patients with 
coronary artery disease and depressed left ventricular function. The hormone was 
administered as an intravenous bolus of 0.8 microgram per kilogram of body 
weight when the aortic cross-clamp was removed after the completion of bypass 
surgery and then as an infusion of 0.113 microgram per kilogram per hour for six 
hours. Clinical and hemodynamic responses were serially recorded, as was any 
need for inotropic or vasodilator drugs.
RESULTS: The patients' preoperative serum triiodothyronine concentrations were 
normal (mean [+/- SD] value, 81 +/- 22 ng per deciliter [1.2 +/- 0.3 nmol per 
liter]), and they decreased by 40 percent (P < 0.001) 30 minutes after the onset 
of cardiopulmonary bypass. The concentrations in patients given intravenous 
triiodothyronine became supranormal and were significantly higher than those in 
patients given placebo (P < 0.001). However, the concentrations were once again 
similar in the two groups 24 hours after surgery. The mean postoperative cardiac 
index was higher in the triiodothyronine group (2.97 +/- 0.72 vs. 2.67 +/- 0.61 
liters per minute per square meter of body-surface area, P = 0.007), and 
systemic vascular resistance was lower (1073 +/- 314 vs. 1235 +/- 387 
dyn.sec.cm-5, P = 0.003). The two groups did not differ significantly in the 
incidence of arrhythmia or the need for therapy with inotropic and vasodilator 
drugs during the 24 hours after surgery, or in perioperative mortality and 
morbidity.
CONCLUSIONS: Raising serum triiodothyronine concentrations in patients 
undergoing coronary-artery bypass surgery increases cardiac output and lowers 
systemic vascular resistance, but does not change outcome or alter the need for 
standard postoperative therapy.