THE EFFECTS OF ISOFLURANE ON REGIONAL MYOCARDIAL-CONTRACTILITY AND METABOLISM IN STUNNED MYOCARDIUM IN ACUTELY INSTRUMENTED DOGS

The sustained dysfunction of myocardial contractility after short peri ods of coronary artery occlusion and reperfusion is termed ''stunned m yocardium.'' Isoflurane may improve the recovery of regional myocardia l contractility in stunned myocardium. The purpose of the present stud y was to determine the effects of isoflurane on 1) the restoration of regional myocardial contractility and 2) the high-energy phosphate met abolism in an acute canine model. To evaluate the effects of isofluran e on the recovery of regional myocardial contractility in stunned myoc ardium, the left anterior descending coronary artery (LAD) was occlude d for 15 min and then reperfused for 60 min during isoflurane (1.5% en d-tidal concentration) anesthesia. Regional myocardial contraction was evaluated by ultrasonic segment shortening (SegS), systolic shortenin g (SysS), and postsystolic shortening (PSS) measurements. High-energy phosphate metabolites were measured at 60 min after reperfusion in ano ther group using full-thickness samples of myocardium obtained from th e reperfused area (supplied by the LAD), and the nonischemic area (sup plied by the left circumflex coronary artery). The concentrations of a denosine monophosphate (AMP), adenosine diphosphate (ADP), adenosine t riphosphate (ATP), creatine phosphate (CP), and lactate in the endocar dial portion of the myocardium were measured and the energy charge pot ential (ECP) was calculated. After 60 min of reperfusion percent SegS was 67.7% +/- 6.6% vs 23.9% +/- 9.4%, isoflurane and control, respecti vely; percent SysS was 67.4% +/- 6.3% isoflurane vs 29.3% +/- 7.4% con trol; and percent PSS was 10.5% +/- 4.6% isoflurane vs 40.5% +/- 8.8% control. ATP in the reperfused area decreased in both anesthetic group s but was higher in the isoflurane (88.2%) compared to the control gro up (77.4%). Lactate concentration in the reperfused area were higher i n both anesthetic groups (168% isoflurane vs 166% control) as compared with the nonischemic area, but these differences were not significant between the anesthetic groups. Isoflurane improved the regional myoca rdial contraction (increased SysS and SegS and decreased PSS) and pres erved the high energy phosphate concentrations in this canine model of myocardial stunning.