title: The oxygen consumption paradox of "stunned myocardium" in dogs.
abstract: The contractile state of the heart is a major determinant of myocardial oxygen consumption. Since regional myocardial contractility can be severely impaired following a transient coronary occlusion, post-ischemic myocardium is frequently assumed to consume less oxygen. To test this assumption, regional myocardial function and oxygen consumption were studied in anesthetized dogs during 2 h of myocardial reperfusion following either a 15-min (Group I) or 4-h (Group II) left anterior descending coronary artery occlusion. Both groups developed similar post-ischemic regional dysfunction characterized by paradoxical motion (negative shortening). Measured as a percent of baseline segment shortening, anterior wall function in Group I (n = 8) and Group II (n = 5) at 30 min of reperfusion was -33 +/- 11% and -34 +/- 16% (p = NS) and at 120 min was -23 +/- 9% and -40 +/- 16% (p = NS). However, the two groups showed a marked difference in regional myocardial oxygen consumption during reperfusion. Despite the abnormal wall motion, regional oxygen consumption in Group I at 30 and 120 min of reperfusion was unchanged from pre-ischemic levels as measured as a percent of baseline: 104 +/- 20% (p = NS) and 111 +/- 21% (p = NS). In contrast, regional oxygen consumption in Group II was markedly depressed from baseline at 30 and 120 min of reperfusion: 42 +/- 7% (p less than .01) and 40 +/- 8% (p less than .01). To determine whether the dissociation between regional myocardial oxygen consumption and function in Group I was related to mitochondrial uncoupling, six additional dogs were studied. Tissue samples were obtained from post-ischemic myocardium after 120 min of reperfusion following a 15-min coronary artery occlusion, and compared to non-ischemic myocardium. There were no differences in the in vitro mitochondrial respiratory rates or oxidative phosphorylation capacity between the post-ischemic and non-ischemic myocardium. Therefore, in the post-ischemic myocardium, significant depressions in regional contractility may not be associated with falls in oxygen consumption. Following a 15-min coronary artery occlusion, the injured myocardium maintains a paradoxically high oxygen consumption with normal mitochondrial function despite decreased contractility and abnormal wall motion.
authors.affiliation: Department of Internal Medicine, University of Michigan, Ann Arbor.
authors.forename: E N
authors.initials: EN
authors.lastname: Dean
authors.forename: M
authors.initials: M
authors.lastname: Shlafer
authors.forename: J M
authors.initials: JM
authors.lastname: Nicklas
mesh_terms: D000818:Animals; D003326:Coronary Circulation / Q000502:physiology; D003327:Coronary Disease / Q000503:physiopathology*; D004285:Dogs; D006352:Heart Ventricles / Q000503:physiopathology; D008297:Male; D008929:Mitochondria, Heart / Q000502:physiology; D008955:Models, Cardiovascular; D009200:Myocardial Contraction / Q000502:physiology*; D009203:Myocardial Infarction / Q000503:physiopathology; D009206:Myocardium / Q000378:metabolism*; D010101:Oxygen Consumption / Q000502:physiology*