3,5,3'-TRIIODO-L-THYRONINE PRETREATMENT WITH CARDIOPLEGIC ARREST AND CHRONIC LEFT-VENTRICULAR DYSFUNCTION

Background. The active form of thyroid hormone, T-3, may be an important determinant of left ventricular (LV) function after hypothermic cardioplegic arrest and rewarming, particularly in patients with preexisting LV dysfunction. Thus, the present project tested the hypothesis that T-3 pretreatment will. improve myocyte contractile performance after hypothermic cardioplegic arrest and rewarming in the setting of chronic LV dysfunction. Methods. Control LV porcine myocytes (n = 160) and cardiomyopathic LV (rapid pacing for 3 weeks at 240 beats/min) myocytes (n = 100) were treated with or without 80 pmol/L T-3. Myocytes then were maintained in normothermic conditions (2 hours at 37 degrees C in media) or exposed to hypothermic cardioplegic arrest ([K+], 24 mmol/L; 2 hours at 4 degrees C) with subsequent rewarming. Results. After cardioplegic arrest and rewarming, T-3 pretreatment increased myocyte velocity of shortening by 41% in control myocytes and by 35% in cardiomyopathic myocytes when compared to untreated myocytes. Furthermore, T-3 pretreatment followed by beta-adrenergic receptor stimulation with isoproterenol (25 nmol/L) improved myocyte velocity of shortening by 24% in control myocytes and 90% in cardiomyopathic myocytes after hypothermic cardioplegic arrest and rewarming, as compared with untreated myocytes. Conclusions. In summary, this study provides evidence to suggest that preemptive treatment with T-3 may improve LV pump function and beta-adrenergic responsiveness after hypothermic cardioplegic arrest and rewarming in patients with underlying LV dysfunction.