Preserved myocardial blood flow and oxygen supply-demand balance with active coronary perfusion during simulated off-pump coronary artery bypass grafting.
BACKGROUND
During off-pump coronary artery bypass surgery, concern remains about the possible myocardial injury associated with the transient occlusion and stabilization of the target vessels. Although intraluminal shunts are used to avoid ischemia during graft anastomosis, blood flow through the shunts can be affected by upstream pressure and inherent resistance, resulting in reduced blood flow during hypotension or severe proximal stenosis.


METHODS
In anesthetized dogs regional myocardial blood flow (microspheres), oxygen consumption, lactate extraction, and systolic shortening (sonomicrometry) were measured in the myocardium served by the left anterior descending coronary artery with native perfusion after interposition of a 2.25-mm shunt (> or = 90% of left anterior descending diameter) and during active coronary perfusion with a constant flow pump. Measurements were made under normotension and hypotension produced by partial caval occlusion to reduce arterial pressure by 50%.


RESULTS
Interposition of the shunt reduced blood flow by 67.8%, regional oxygen delivery by 59.8%, and systolic shortening by 45.6% relative to baseline, but lactate extraction (31.0% vs 31.2%) and oxygen supply-consumption (O(2)S/myocardial oxygen consumption ratio, 2.7 +/- 0.5 vs 2.6 +/- 0.5) were comparable with baseline values. Hypotension further decreased these physiologic values and was associated with local lactate production (-67.4% extraction) and decreased O(2)S/myocardial oxygen consumption ratio (1.3 +/- 0.1). Active coronary perfusion was associated with regional blood flow, oxygen delivery, systolic shortening, and lactate extraction comparable with baseline values. In contrast to the shunt, active perfusion maintained myocardial flow, oxygen delivery, and lactate extraction during hypotension and normalized the O(2)S/myocardial oxygen consumption ratio, although systolic shortening decreased as a result of ventricular unloading.


CONCLUSIONS
Intraluminal shunts may impede oxygen delivery to the target myocardium, which precipitates regional ischemia during transient hypotension. Active coronary perfusion provides adequate oxygen supply independent of systemic blood pressure.
Muraki
Satoshi
S
Section of Cardiothoracic Surgery, Carlyle Fraser Heart Center, Emory University School of Medicine, Atlanta, GA 30308-2225, USA.
Morris
Cullen D
CD
Budde
Jason M
JM
Otto
Rachel N
RN
Zhao
Zhi-Qing
ZQ
Puskas
John D
JD
Guyton
Robert A
RA
Vinten-Johansen
Jakob
J
D000818:Animals; D001794:Blood Pressure; D001026:Coronary Artery Bypass / Q000379:methods; D003326:Coronary Circulation; D004285:Dogs; D006339:Heart Rate; D009200:Myocardial Contraction; D009206:Myocardium / Q000378:metabolism*; D010100:Oxygen / Q000097:blood*; D010101:Oxygen Consumption; D010477:Perfusion / Q000295:instrumentation
D010100:Oxygen