Ischemic Preconditioning Increases Myocardial Tolerance to Subsequent Ischemic Episodes

It has long been recognized that a brief episode of myocardial ischemia causes reversible myocyte injury, "reversible" being defined by the fact that early restoration of arterial flow prevents infarction and permits eventual restoration of normal myocardial structure, function, and metabolism. However, numerous studies during the last 15 years1-5 have revealed that complete recovery is not immediate; in a variety of experimental models, profound metabolic and functional abnormalities may persist for hours or days after as little as 5-15 minutes of coronary occlusion. For example, a 15-minute episode of coronary occlusion in dogs results in 1) increases in tissue water and potassium content that persist for at least 1 hour,1 2) substantial loss of adenine nucleotides,' which are not fully resynthesized for as long as 4 days,2'3 and 3) postischemic contractile dysfunction that may persist for 2-4 days. The latter phenomenon, first reported by Heyndrickx et a14 and later termed "myocardial stunning" by Braunwald and Kloner,5 has been the subject