Anemia in Chronic Heart Failure

Abstract

Anemia occurs commonly in patients with chronic heart failure (CHF) and has been proposed as a novel therapeutic target in this patient population. The present review will summarize the current knowledge of the prevalence, causative factors, and pathophysiological correlates of anemia in CHF. Potential risks and benefits of therapy with erythropoietic agents for the treatment of anemia in CHF will also be discussed. Prevalence of Anemia in CHF Estimates of the prevalence of anemia in patients with CHF and low ejection fraction range widely from 4% to 61% (median 18%).1–15 Variability in estimated prevalence is partly attributable to use of inconsistent definitions of anemia in individual reports. The World Health Organization definition of anemia (hemoglobin concentration 13.0 g/dL in men and 12.0 g/dL in women) takes into account known gender differences in distribution of hemoglobin values, 16 whereas the National Kidney Foundation defines anemia as hemoglobin 12 g/dL in men and postmenopausal women. 17 These standard definitions of anemia are not based on wellestablished physiological or population norms. Published reports in CHF populations have used these and other study-specific definitions of anemia (including other arbitrary or statistically defined hemoglobin and hematocrit categories and administrative diagnostic codes from hospital records). Despite these inconsistencies in the definition of anemia cases, most studies indicate that the prevalence of anemia is increased in CHF populations with comorbid kidney disease, advanced age, and more severe symptoms (range, 30% to 61%) when compared with less symptomatic ambulatory populations (range, 4% to 23%). In patients with CHF and preserved ejection fraction, the few published reports indicate that anemia is also highly prevalent in this group.18–20 Underlying Cause of Anemia in CHF Anemia occurs when there is a deficiency in new erythrocyte production relative to the rate of removal of aged erythrocytes. Erythropoietin, a 30.4-kDa glycoprotein growth factor produced primarily by kidney, is the key component of the homeostatic system for regulation of red blood cell mass and tissue oxygen delivery.21–24 Erythropoietin prevents the programmed cell death of erythrocyte progenitor cells and thereby stimulates their proliferation, maturation, and terminal differentiation. 23 Any abnormality that reduces renal secretion of or bone marrow response to erythropoietin may result in anemia. Iron deficiency is present in 30% of anemic patients with CHF, so the majority of observed anemia is normocytic, often classified as anemia of chronic disease. Clinical characteristics commonly associated with increased risk of anemia in CHF populations are listed in the Table. Although risk factors for anemia identified in cross-sectional studies do not provide evidence of a causal link, these observations suggest that several distinct mechanisms may commonly contribute to anemia in patients with CHF. Several of the most important potential causal pathways will be discussed briefly below and are summarized in Figure 1. Chronic kidney disease is a common comorbidity in patients with CHF and is a strong independent predictor of increased risk of anemia in several studies. In chronic kidney disease populations without heart failure, moderate to severe kidney disease (defined as glomerular filtration rate [GFR] 60 mL/min) is associated with diminished erythropoietin production and a progressive decrease in hemoglobin values that is linearly related to reduction in GFR.25 The estimated prevalence of at least moderate chronic kidney disease (defined as GFR 60 mL/min) in CHF populations is 20% to 40%. 4,9,26,27 Anemia is frequently associated with decreased body mass index in published reports, a finding that suggests that patients with cachexia are at greater risk for anemia. Serum levels of proinflammatory cytokines are increased in cachectic patients with CHF and may contribute to development of anemia by several mechanisms. Proinflammatory cytokines including tumor necrosis factor- (TNF-), interleukin-1, and interleukin-6 have been shown to disrupt multiple aspects of erythropoiesis, including reduction of renal erythropoietin secretion, suppression of erythropoietin activity in red blood cell precursors in the bone marrow level, and reduction of bioavailability of iron stores for hemoglobin synthesis.28–31 Proinflammatory cytokines also increase levels of the liverderived peptide hormone, hepcidin.32,33 Hepcidin interacts with ferroportin and other iron transport proteins in the enterocyte to inhibit gut iron absorption and thereby reduces iron bioavailability for hemoglobin synthesis. 32,33 In a mouse