Coronary blood flow and myocardial reactive hyperemia in the ischemic dog heart

Restoring blood flow may or may not reverse ischemic myocardial injury, depending on the duration and severity of ischemia. To investigate methods for predicting reversibility of myocardial damage, coronary blood flow and reactive hyperemic responses (RHR) were assessed after the left circumflex coronary artery was reopened following 20, 60, or 120 minutes of occlusion in 45 anesthetized dogs. After a 20 minute occlusion, cell injury was reversible. Blood flow and RHR were high initially and stabilized near preocclusion levels. After 60 or 120 minute occlusions, which caused irreversible infarction, initial coronary flows were also high. However, 2 hours after revascularization flow averaged only 65 percent of preocclusion levels and fell to 55 percent after 4 hours. In 80 percent of these dogs flow patterns became nonpulsatile and reached zero flow in several. RHR measured within minutes of vessel reopening following 60 or 120 minute occlusions was greatly reduced and returned to an average of only 36 percent of control values one hour after reopening compared to 80 percent in the 20 minute occlusion group. RHR predicted the eventual recovery of the myocardium within minutes after restoration of flow, whereas this could not be detected by coronary flow measurements alone.