Red Blood Cell Transfusion in Patients With Coronary Artery Disease (CAD)

Patients with a low blood count (anemia) with stable or unstable coronary artery disease consistently show worse clinical outcomes. It is unclear whether this association is confounded since anemic patients tend to be also sicker i.e. have lower ejection fractions or more comorbidities and this would be the reason for the worse outcomes rather than anemia. The coronary arteries are a unique vascular bed insofar that across the cardiac circulation oxygen extraction is close to maximal at rest. Thus increases in demand can only be met by increases in blood flow and hemoglobin concentration since oxygen extraction is maximal at rest. It is natural to assume that maximization of oxygen delivery in the setting of active coronary syndrome (ACS) is beneficial to the patient since oxygen extraction and coronary blood flow is fixed. In fact, in most intensive care units patients with ACS are transfused to a HCT of 30%. However, retrospective analysis of trial data showed at best mixed results in clinical outcome when patients with ACS were transfused and in fact in some studies showed consistently worse outcomes than non-transfused patients. Similar disappointing results have recently published in patient who underwent coronary artery bypass grafting (CABG). This study is designed to determine the effect of red blood cell (RBC) transfusion on oxygen consumption, cardiac, microcirculatory and endothelial function in patients with active coronary artery disease. For this study active coronary artery disease will be defined as the patient having undergone within the past 4 days of recruitment either a myocardial infarction due to atherothrombosis (AHA type I myocardial infarction) or surgery for coronary artery bypass grafting. In specific this study will test the hypothesis whether RBC transfusions improves cardiac and vascular function in patients with a hematocrit of less than 30% with active coronary artery disease. Aims of this study are to determine whether RBC transfusion in patients with active coronary artery disease and anemia: * increases oxygen delivery to the peripheral tissues. * increases whole-body oxygen consumption. * decreases nitric oxide bioavailability, endothelial, microcirculatory, and myocardial function, and/or increases platelet aggregation