BETA-BLOCKADE AS AN ALTERNATIVE TO CARDIOPLEGIC ARREST DURING CARDIOPULMONARY BYPASS IN DOGS

Abstract

S115 Introduction: As an alternative to cardioplegic arrest, cardiac surgical conditions have been reported using beta-blocker induced minimal myocardial contraction (MMC) during cardiopulmonary bypass. [1] The technique of MMC involves the use of high dose intravenous esmolol to suppress myocardial chronotropy and inotropy sufficiently to provide cardiac surgical conditions. The purpose of this study was to compare conventional crystalloid cardioplegic arrest (CA) to MMC in terms of ischemia avoidance, myocardial edema formation, and cardiac function. Methods: All procedures were approved by The University of Texas Animal Welfare Committee. Twelve dogs were placed on cardiopulmonary bypass. Six dogs were subjected to crystalloid cardioplegic arrest for two hours. Surgical conditions were produced in the other 6 dogs for 2 hours with intravenous esmolol avoiding aortic clamping and cardioplegia. Arterial and coronary sinus lactate concentrations were determined as a gauge of myocardial ischemia. Myocardial water content was determined from endomyocardial biopsies by a microgravimetric technique using a linear density gradient. Preload recruitable stroke work (PRSW), a measure of contractility, was calculated using left ventricular pressure-volume loops derived from sonomicrometry and micromanometry. Results: Significant lactate washout was demonstrated following cardioplegic arrest but not following MMC. Myocardial water content was significantly less during and after MMC compared to cardioplegic arrest (Table 1). Preload recruitable stroke work was decreased compared to baseline in both groups (P<0.05).Table 1: Myocardial Water Content (%)Discussion: In contrast to a previous study involving one hour of MMC, ventricular function was decreased to the same extent as the cardioplegic arrest group following two hours of MMC. This was attributed to the accumulation of ASL-8123, the primary metabolite of esmolol which possesses beta-antagonist properties. While post-bypass ventricular function is similar in both groups, MMC appears to be superior in terms of ischemia avoidance and myocardial edema minimization.