Cardiac and skeletal muscle myoglobin release after reperfusion of injured myocardium in dogs with systemic hypotension.
BACKGROUND
Myoglobin (Mb) is an intramyocardial protein that is released into the systemic circulation and rapidly cleared via the kidneys after myocardial injury. Arterial Mb concentration-time curves have been studied in humans and dogs in the setting of acute coronary artery occlusion, and the rate of rise of Mb is both sensitive and specific as an indicator of successful coronary artery reperfusion. Systemic hypotension may alter Mb kinetics and impact on the utility of this method by causing Mb release from ischemic skeletal muscle and by decreasing renal Mb clearance. This study was undertaken to determine whether analysis of Mb kinetics remains accurate in identifying coronary reperfusion in the setting of systemic hypotension.


RESULTS
Eighteen chronically instrumented dogs were made hypotensive by being bled via a large-bore femoral artery catheter into a reservoir adjusted to maintain a constant mean arterial pressure of 50 mm Hg for 8 hours. After the first hour of hypotension, each dog was studied under one of the following three protocols: group 1, 2 hours of mid-left anterior descending artery (LAD) occlusion followed by 5 hours of unlimited reperfusion; group 2, 7 hours of mid-LAD occlusion without reperfusion; or group 3, 7 additional hours of hypotension alone. Systemic lactate extractions demonstrated a shift to anaerobic metabolism in skeletal muscle and confirmed that shock was established in all animals. Regional arteriovenous Mb differences in group 1 animals demonstrated release of large amounts of Mb from reperfused myocardium; in contrast, smaller amounts of Mb were released both from skeletal muscle rendered ischemic by hypotension and from myocardium rendered ischemic by coronary occlusion without reperfusion. In group 1 dogs, arterial Mb rose rapidly immediately after reperfusion, with peak Mb occurring 108 +/- 24 minutes (mean +/- SEM) after vessel reopening. In group 2 and group 3 dogs, arterial Mb rose more slowly, such that peak Mb was not reached within 8 hours in 11 of 12 animals. The linear rate of rise of arterial Mb over the first hour of reperfusion in group 1 dogs was 51 +/- 16 ng.mL-1.min-1. This slope was significantly greater than slopes determined over the same time period in dogs occluded and not reperfused (group 2, 1.2 +/- 0.6 ng.mL-1.min-1) and in those hypotensive alone (group 3, 0.8 +/- 0.5 ng.mL-1.min-1). All the slopes of group 2 and group 3 dogs fell below the range of slopes of group 1 dogs. In contrast to slopes of the Mb concentration-time curves, linear creatine kinase slopes were significantly less sensitive in predicting reperfusion.


CONCLUSIONS
Analysis of plasma Mb kinetics allows early identification of coronary reperfusion after myocardial injury even in the presence of significant systemic hypotension.
Spangenthal
E J
EJ
Department of Veterans Affairs Medical Center, Buffalo, NY 14215, USA.
Ellis
A K
AK
D000818:Animals; D003402:Creatine Kinase / Q000378:metabolism; D004285:Dogs; D006439:Hemodynamics; D007022:Hypotension / Q000150:complications*; D007700:Kinetics; D007773:Lactates / Q000378:metabolism; D018482:Muscle, Skeletal / Q000378:metabolism*; D009203:Myocardial Infarction / Q000150:complications* / Q000378:metabolism* / Q000503:physiopathology; D015425:Myocardial Reperfusion; D009206:Myocardium / Q000378:metabolism*; D009211:Myoglobin / Q000378:metabolism*; D013997:Time Factors
D007773:Lactates; D009211:Myoglobin; D003402:Creatine Kinase