Boston, MA- Anemia has been shown to be present in patients with acute myocardial infarction and other acute coronary syndromes (ACS). Anemia can worsen these conditions by decreasing the oxygen content of the blood supplying the myocardium or by increasing the myocardial oxygen demand. In a study done by Marc Sabatine, MD, MPH et al from Brigham and Women’s Hospital, baseline hemoglobin concentration was compared in patients with ACS. They found anemia to be a powerful and independent predictor of major adverse cardiovascular events in patients with ACS.  

The study examined the association between baseline hemoglobin concentration and a range of cardiovascular clinical outcomes in a broad cohort of 39,922 patients across the spectrum of ACS. A total of 25,419 patients with STEMI and 14,503 patients with NSTE ACS whose baseline hemoglobin data was available were examined. These patients were divided into categories based upon increments of their hemoglobin levels.  

In patients with STEMI, the likelihood of hypotension, tachycardia and Killip class II or IV was significantly related to baseline hemoglobin (P<0.001), with patients at either end of the hemoglobin spectrum having a higher likelihood of hemodynamic disarray. After adjustments for baseline characteristics, it was found a reverse J shaped relationship between baseline hemoglobin values and major adverse cardiovascular events. More specifically, in patients with ST-elevation myocardial infarction, cardiovascular mortality increased as hemoglobin levels fell below 14 g/dL (OR of 1.21 and 95% CI 1.12 to 1.30, P<0.001) for each 1-g/dL decrement in hemoglobin. Likewise for patients with hemoglobin values great than 17 g/dL there was also increased mortality (OR 1.79, 95% CI 1.18 to 2.71, P=0.007). In patients with NSTE ACS, the likelihood of cardiovascular death, myocardial infarction or recurrent ischemia increased as the hemoglobin fell below 11 g/dL, with an OP of 1.45 (95% CI 1.33 to 1.58, P<0.001) for each 1 g/dL decrement in hemoglobin. Patients with hemoglobin levels greater than 16 g/dL also had an increased rate of death or ischemic event (OR 1.31, 95% CI 1.03 to 1.66, P=0.027).  

In this broad cohort of patients with ACS, the study found highly significant associations between low hemoglobin concentrations and adverse cardiovascular outcomes, such as prevalence of hypotension, tachycardia and Killip class II or IV. Among patients with STEMI, there was an increase in mortality and heart failure as the baseline hemoglobin dropped below 14 g/dL. In patients with NSTE ACS, and increased odds ratio of cardiovascular death, MI or recurrent ischemia became apparent when the baseline hemoglobin fell below 11 g/dL.  

Anemia has been shown to significantly decrease oxygen delivery to the myocardium and increase the myocardial oxygen demand through necessitating a higher stroke volume and heart rate. The combination of these processes may explain the pathophyiology underlying the progressively worse outcomes observed in patients with ACS and lower baseline hemoglobin concentrations. In patients with very high hemoglobin levels (>17 g/dL), the increase in blood viscosity can lead to an increase in coronary vascular resistance and a decrease coronary blood flow, which can ultimately lead to thrombosis and MI. 

Co-authors: David A. Morrow, MD, MPH; Robert Giugliano, MD, SM; Paul B.J. Burton, MBBS, PhD; Sabina A. Murphy, MPH; Carolyn H. McCabe, BS; C. Michael Gibson, MS, MD; Eugene Braunwald, MD