Time course of recovery of "stunned" myocardium following variable periods of ischemia in conscious and anesthetized dogs.

Persistence of regional contractile dysfunction after restoration of blood flow to transiently ischemic myocardium has been well described. To date, most studies have been performed in anesthetized animals. The present investigation compared the time course of recovery of regional segment shortening (percentage of segment shortening) in anesthetized versus conscious dogs subjected to a brief period of total occlusion of the left anterior descending coronary artery. Periods of occlusion lasting 5, 10, and 15 minutes were followed by 3 hours of reperfusion. Dogs anesthetized with sodium pentobarbital (30 mg/kg intravenously) had a significantly higher heart rate and blood pressure and lower dP/dt than conscious dogs. Coronary artery occlusion resulted in similar degrees of regional dyskinesis or akinesis, indicative of severe myocardial ischemia, in all experiments. During reperfusion, a gradual return of contractile function toward baseline was observed. At the end of the first 15 minutes of reflow, dogs subjected to 5 minutes of coronary occlusion demonstrated approximately 70% of control segment shortening in the previously ischemic zone. Animals subjected to 10- and 15-minute periods of coronary artery occlusion showed approximately 60% and 40% of control segment shortening at the same time point, respectively. The remainder of the 3-hour reperfusion period was characterized by a more gradual recovery of regional segment function. No differences were observed between anesthetized and conscious animals. It is concluded that the time course of functional recovery of postischemic reperfused myocardium is directly related to the duration of coronary occlusion and is similar in conscious and anesthetized dogs.