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.