Esmolol and cardiopulmonary bypass during reperfusion reduce myocardial infarct size in dogs

Background. Infarct size can be reduced by beta -blockade in acute myocardi al ischemia. However it is unknown whether myocardial salvage is still effe ctive when beta -blockade is limited to reperfusion. Methods. After initiation of cardiopulmonary bypass, 20 dogs were submitted to 2 hours of regional left ventricular ischemia, followed by 2 hours of r eperfusion. In 11 dogs beta -blockade was started with the onset of reperfu sion (esmolol group). The remaining dogs received no treatment (control, n = 9). Infarct size was determined by tetrazolium chloride staining. Myocard ial water content (MWC) and ultrastructural damage (electronmicroscopy) wer e determined from transmural biopsies. Results. Infarct size was significantly smaller in the esmolol group compar ed with control (49% versus 68%, p < 0.05). After 2 hours ischemia there wa s no difference in MWC between groups, whereas after 2 hours reperfusion MW C of ischemic myocardium was significantly lower in the esmolol group than in the control (p < 0.05). Ultrastructural changes were typical for ischemi a-reperfusion injury in both groups. Conclusions. beta -Blockade may be cardioprotective during reperfusion thro ugh various mechanisms and may enhance myocardial salvage, even when treatm ent is initiated as late as with the onset of reperfusion. (C) 2001 by The Society of Thoracic Surgeons.