Is esmolol cardioprotective? Tolerance of pacing tachycardia, acute afterloading and hemodilution in dogs with coronary stenosis.
The aim of this study was to determine whether esmolol, an ultrashort-acting beta-adrenergic antagonist, possesses cardioprotective properties unrelated to a concomitant decrease in heart rate. Previous studies have demonstrated beneficial effects of beta-adrenergic blocking agents with unchanged heart rates. The effect of esmolol (100 micrograms/kg per min) on the response of global cardiovascular and regional myocardial contractile function (sonomicrometry) to pacing-induced tachycardia and acute left ventricular afterloading was assessed in dogs with a critical stenosis of the left anterior descending coronary artery (LAD). These responses were observed at the baseline hemoglobin level (12.5 +/- 0.3 g/100 ml) as well as after hemodilution-induced mild regional contractile dysfunction (7.4 +/- 0.4 g/100 ml) in the area supplied by this artery (LAD area). Data were analyzed by using a repeated measures multivariate analysis of variance with complete block design treating pacing rate and afterloading, respectively, as the repeated measure. Esmolol decreased the maximal first derivative of left ventricular pressure (dP/dtmax); global cardiovascular and regional myocardial contractile function were otherwise unchanged. Esmolol did not alter the response of global cardiovascular or regional myocardial function to pacing-induced tachycardia or to acute left ventricular afterloading, both at the baseline hemoglobin level as well as during mild hemodilution-induced LAD area contractile dysfunction. At an infusion rate of 100 micrograms/kg per min we were unable to demonstrate cardioprotective esmolol effects in a canine model of critical coronary stenosis with controlled heart rate and identical loading conditions.