Facilitated Recovery of Cardiac Performance by Triiodothyronine following a Transient Ischemic Insult

Abstract

Reperfusion following a transient ischemic insult has been shown to result in a delayed recovery of myocardial function. A reduction in plasma triiodothyronine (T₃) has been reported in these acute cardiovascular challenges. To test whether the replacement of T₃ can facilitate the recovery of myocardial function following a transient regional ischemia, we investigated cardiac performance for 3 h after a 15-min, left anterior descending coronary artery occlusion in a canine model. Three groups of dogs were studied: I – control (n = 10); II -receiving T₃ (0.25 µg/kg i.v. and 0.25 µg/kg/h for 3 h, n = 9), and III – receiving T₃ (0.25 µg/kg i.v. and 0.5 µg/kg/h for 3 h, n = 9). Three hours following reperfusion, the T3 level in blood was significantly decreased in group I. Concomitantly, local segmental shortening was reduced from preocclusion control levels in group I (15.2 to 5.1%, p < 0.05), but recovered in both treated groups. The endsystolic elastance (Ees) and the external work (EW) efficiency (EW/PVA) in group I were depressed from preocclusion control (Ees = 95.5 ± 0.8%; EW/PVA = 90.2 ± 1.8%, both p < 0.05), the effective arterial elastance (Ea) and ventriculoarterial coupling (Ea/Ees) in group I were still elevated from preocclusion control (Ea = 122.5 ± 5.1%; Ea/Ees =128.3 ± 5.3%, both p < 0.05). But these measures of global cardiac performance in the treated groups recovered following reperfusion, and the extent of recovery was dose dependent. These data suggest that T₃ facilitates recovery of the stunned myocardium by improvement in local and global contractile function, in ventriculoarterial coupling, and in the energy efficiency.

Impact of Triiodothyronine on the Survival of High-Risk Patients Undergoing Open Heart Surgery

“…This rapid response is of great relevance to cardiac surgery [39][40][41]. This rapid recovery was also observed after inducing myocardial stunning in dogs [20]. By using load-independent pressure-volume relationship and sonomicrometers T3 allowed total recovery of the myocardial dysfunction.…”

“…There is a generalized body inflamma tory response [10], complement activation, interleukin production and a profound derangement of the thyroid profile lasting for several days [11,12], The 'euthyroid sick syndrome' is characterized by a low FTy, increase in plasma reverse Ty (rTy), normal or low total Ty (TTy), thy roxine (T4), and thyroid-stimulating hormone (TSH) lev- . In sick patients, the lower the n y r T j ratios cor related with higher mortality [ 14,15], Experimental administration of T 3 in animals has shown a rapid reversal of the myocardial dysfunction which follows transient ischemic events, such as: (a) in duction of experimental brain death [16][17][18], (b) stunned myocardium [19,20], or (c) after prolonged cardioplégie arrest on cardiopulmonary bypass (CPB) [21,22], Similar observations were made in our preliminary clinical stud ies. After administering T3 to 10 patients who were expe riencing profound postcardiotomy myocardial depres sion, the T3 enhanced the reversal of the myocardial dys function allowing for discontinuation of CPB, and also the use of intra-aortic balloon pump was no longer neces sary after 1 h. This therapy also allowed for a rapid reduc tion in high inotropic requirements [23].…”

Efficiency of energy transfer, but not external work, is maximized in stunned myocardium

“…As a consequence, the working point was now similar to EW max . To the best of our knowledge, only relative changes in ventriculo-arterial coupling ratio have been reported after regional stunning (30). From these data it cannot be concluded whether power was maximized before or after stunning.…”