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Thyroid hormone administration in chronic heart failure and in patients
undergoing cardiovascular procedures
In heart failure, alterations in thyroid hormone metabolism may contribute
to defective myocardial performance. Accordingly, thyroid hormone increases
cardiac output by enhancing myocardial contractile performance and decreasing
venous compliance (104). Favourable results were also obtained with 3,5-
diiodothyropropionic acid, a cardiotonic thyroid hormone analogue given
in combination with captopril. Furthermore, two placebo-controlled trials
(105,106) showed that administration of 100µg T4/day improved
cardiac and exercise performance in patients with idiopathic dilated cardiomyopathy.
The responses of cardiac output and heart rate to dobutamine infusion were
also enhanced, probably due to an upregulation of b1 receptors. Functional
capacity markedly improved, together with an increase in peak exercise
cardiac output.
Cardiopulmonary bypass results in a nonthyroidal illness syndrome with acute lowering of serum T3 levels (107). T3 administration to correct the decreased T3 levels has been applied in several reports using small patient numbers and improved cardiovascular function has been described (108,109). However, two randomised controlled studies showed that T3 administration immediately following coronary artery bypass surgery to patients at high risk for impaired cardiac contractility did not alter most hemodynamic variables studied, the requirement for post-operative adjunctive inotropic agents, or the frequency of the requirement for intra-aortic balloon counterpulsation (110,111). The frequency of ventricular arrhythmia, hours to extubation, time in the intensive care unit, total hospital stay, or overall mortality were also not altered in the T3 group compared with the control group. These two studies strongly suggest that T3 administration should not be used routinely in patients undergoing coronary artery bypass surgery. Thus, the overall usefulness of acute T3 administration in the setting of invasive cardiovascular procedures is not established currently. |
