May 5, 2005
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 |