THE EFFECTS OF AMRINONE VERSUS DOBUTAMINE ON MYOCARDIAL MECHANICS ANDENERGETICS AFTER HYPOTHERMIC GLOBAL-ISCHEMIA

The effects on the postischemic myocardium of amrinone and dobutamine were studied in canine hearts that underwent 90 minutes of hypothermic (10-degrees-C) arrested ischemia. In an isolated heart preparation cr oss-circulated by a support dog, left ventricular pressure-volume loop s were collected under a constant afterload based on a mock circulator y system and a range of preload conditions controlled by a computerize d servo volume pump. Dobutamine (0, 5, 10, 15 mug/kg per minute) and a mrinone (0, 0.75, 1.5, 3.0 mg/kg) were tested in this order based on t he weights of the support dogs in eight experiments. Changes in intrin sic myocardial contractility were analyzed as percent increases in the preload recruitable stroke work area from baselines. Dobutamine exhib ited significant dose-related increases in the preload recruitable str oke work area. Amrinone did not produce significant increases in prelo ad recruitable stroke work area at 0.75 mg/kg; amrinone's inotropic ef fect was equivalent to dobutamine, 5 mug/kg per minute at 1.5 mg/kg, a nd at the maximum dose (3.0 mg/kg) it was equivalent to dobutamine, 10 mug/kg per minute. The myocardial energetic efficiency was determined from the analysis of the myocardial oxygen consumption-pressure volum e area relationship. The y intercept represents the basal metabolic ox ygen requirement of the unloaded beating heart, and the slope is inver sely proportional to the rate of energy conversion for increasing load ing conditions. Dobutamine significantly increased the y intercepts, b ut it had no effects on the slopes. These changes demonstrate reduced myocardial efficiencies that are consistent with previous reports. Amr inone (0.75 and 1.50 mg/kg) did not result in change of the y intercep ts and the slopes of myocardial oxygen consumption-pressure-volume are a relationship from baseline conditions. The y intercept was increased with amrinone (3.0 mg/kg), although still not significantly higher th an baseline and not to the extents of the dobutamine group. Dobutamine did not have any primary effect on coronary resistance, while amrinon e significantly reduced coronary resistance in all loading conditions at 1.5 and 3.0 mg/kg. This study demonstrates that the inotropic effec ts of amrinone tested under this constant afterload preparation were l ower than those of dobutamine. Amrinone has a superior profile of myoc ardial efficiency on the postischemic myocardium since it does not pro duce the oxygen-wasting effects of the traditional inotropic agents su ch as the beta agonists. This benefit, together with amrinone's corona ry dilating effects, critically improves the supply/demand ratio that may be of importance in certain clinical situations.