NoBlood

Nika · #1 (**permalink**) 03-29-2005, 09:52 PM

Commentary: Blood Transfusion and Clinical Outcomes in Patients With Acute Coronary Syndromes

Jeffrey L. Carson, MD
Division of General Internal Medicine
UMDNDJ - Ropbert Wood Johnson Medical School
New Brunswick, New Jersey, USA

In recent years the trend has been to use higher transfusion trigger in patients with cardiovascular disease. Studies in animals undergoing euvolemic hemodilution demonstrate myocardial ischemia at higher hemoglobin concentrations in the presence of coronary artery obstruction than in the absence of coronary artery obstruction.1,2 These findings were confirmed in a cohort of patients undergoing surgery who declined blood transfusion in which patients with underlying cardiovascular disease had higher odds of death than patients without cardiovascular disease.3 In a high-profile publication in 2001, Wu and colleagues analyzed Medicare billing data in 78,000 patients with acute myocardial infarction.4 Mortality was lower in patients who were transfused when the admission hematocrit was below 33%. These studies were consistent with the physiological fact that the heart extracts 60-75% of oxygen from the coronary circulation and in the presence of coronary artery disease cannot augment oxygen delivery by increasing flow.

However, a new study just published in JAMA challenges the premise that patients with coronary artery disease should receive blood transfusion to maintain hemoglobin concentrations in the range of 10-11 g/dL. Rao and colleagues analyzed experience of 24,112 patients enrolled in three clinical trials evaluating different therapeutic interventions in patients with acute coronary syndrome.5 Patients receiving blood transfusion were older and had more frequent co-morbidity. After adjusting for differences in baseline characteristics, patients receiving blood transfusion had about a 3- to 4-fold higher risk of death and death or myocardial infarction than patients not receiving transfusion. Stratifying for nadir hematocrit, the probability of death was 169 times higher when hematocrit was > 30% but not significantly elevated when hematocrit was 25%. This very large difference in risk between patients with hematocrits of 30% and 25% is most likely explained by bias rather than consequences of anemia.

In the accompanying editorial, HÃ©bert and Fergusson comment that observational studies (i.e., Wu and Rao) "do not provide unbiased estimates of the benefits of transfusion when the degree of anemia is directly related to the administration of red blood cells. (â€¦) it is time to undertake randomized clinical trials in different populations of patients with ischemic heart disease."6 Such a trial is funded by the National Heart, Lung, and Blood Institute and has just started enrolling patients.7

References

1. Hagl S, Heimisch W, Meisner H, Erben R, Baum M, Mendler N. The effect of hemodilution on regional myocardial function in the presence of coronary stenosis. Basic Res Cardiol 1977;72:344-64.

2. Wilkerson DK, Rosen AL, Sehgal LR, Gould SA, Sehgal HL, Moss GS. Limits of cardiac compensation in anemic baboons. Surgery 1988;103:665-70.

3. Carson JL, Duff A, Poses RM, et al. Effect of anaemia and cardiovascular disease on surgical mortality and morbidity. Lancet 1996;348:1055-60.

4. Wu WC, Rathore SS, Wang Y, Radford MJ, Krumholz HM. Blood transfusion in elderly patients with acute myocardial infarction. N Eng J Med 2001;345:1230-6.

5. Rao SV, Jollis JG, Harrington RA, et al. Relationship of blood transfusion and clinical outcomes in patients with acute coronary syndromes. JAMA 2004;292:1555-62.

6. Hebert PC, Fergusson DA. Do transfusions get to the heart of the matter? JAMA 2004;292:1610-2.

7. Carson JL, Terrin ML, Barton FB, et al. A pilot randomized trial comparing symptomatic vs. hemoglobin- level-driven red blood cell transfusions following hip fracture. Transfusion 1998;38:522-9.