Inotropic effect of triiodothyronine (T3) in low cardiac output following cardioplegic arrest and cardiopulmonary bypass: an initial experience in patients undergoing open heart surgery

Abstract

A significant reduction in plasma free triiodothyronine (T3) (P lessthan 0.0001) has been observed in patients undergoing open heart surgery.The beneficial effect of T3 would appear to be associated with increasedsynthesis and utilization of myocardial high energy stores. We havetherefore administered T3 (4-10 micrograms iv) to 10 patients either whendifficulty was being experienced in weaning from cardiopulmonary bypass(CPB) support (n = 5), or when myocardial function remained extremely poor(n = 5), despite inotropic and intraaortic balloon pump support. Meanpreoperative NYHA functional class of the 10 patients was 3.2, leftventricular enddiastolic pressure (LVEDP) 20 mm Hg and ejection fraction(EF) 40%. The mean myocardial ischaemia time was 72 min (range 40-120 min).Within 1 h of T3 administration the mean plasma free T3 level had risenfrom 1.03 to 3.56 micrograms/ml and CPB was discontinued in all 5 cases.Balloon pump support (n = 2) was no longer essential within 3 h. At 1 h,the mean arterial pressure (MAP) had risen from 42 to 78 mm Hg, and heartrate (HR) from 90 to 104 beats/min; the left atrial pressure (LAP) hadfallen from 30 to 14 mm Hg, and the central venous pressure (CVP) from 20to 11 cm H2O. (All changes significant at P less than 0.0001.) Inotropicsupport had been significantly reduced or discontinued. To our knowledge,T3 has not been administered previously as an inotropic agent to patientswho have undergone cardiac surgery. We believe that T3 may have animportant role in the rescue of failing hearts following a period ofmyocardial ischaemia in patients who have undergone open heart surgery.