Preconditioning of the heart by repeated stunning: attenuation of post-ischemic dysfunction.

The effect of repetitive brief periods of coronary occlusion on subsequent prolonged ischemic insult was studied using a swine heart model. Four 5-min episodes of left anterior descending coronary artery (LAD) occlusion, each separated by 10 min of reperfusion, did not affect any of the regional or global myocardial functions examined, except that the level of adenosine triphosphate (ATP) dropped to some extent. Sixty minutes of LAD occlusion following four repeated stunnings further reduced the ATP level, but this reduction was significantly lower compared to nonstunned control. Myocardial global functions were not affected significantly by prolonged ischemic insult. Segment shortening (SS) was reduced comparably in both control and stunned groups. However, SS improved significantly during subsequent reperfusion in the stunned group compared to control. The experimental group also demonstrated reduced infarct size and an area of risk compared to nonstunned control. These results indicate that repeated stunning prior to irreversible ischemic insult can attenuate ischemic injury and post-ischemic dysfunction.