Key Points
- Anemia is common among individuals with acute myocardial infarction, however, transfusion thresholds and targets remain uncertain.
- The MINT trial randomized 3,506 patients with acute myocardial and anemia (hemoglobin concentration < 10 g/dL) to a restrictive transfusion strategy (transfusion permitted if hemoglobin was less than 8 g/dL or in the event of anginal symptoms despite medications) or a liberal strategy (transfusion when hemoglobin was less than 10 g/dL).
- At 30-days the primary endpoint of all-cause death or recurrent myocardial infarction was not statistically different between the two strategies.
Anemia is common among individuals with acute myocardial infarction with studies reporting a prevalence ranging from 6% to 43% depending on the definition of anemia used and comorbidity burden of the study population. In several clinical settings, a restrictive transfusion strategy has been as effective as a more liberal transfusion strategy. However, small trials specific to patients with acute myocardial infarction have reported inconsistent findings. On one hand, maintaining a higher hemoglobin concentration, thereby providing more oxygen to vulnerable myocardium, may be beneficial. On the other hand, liberal transfusion may increase blood viscosity and vascular inflammation which may be harmful. Accordingly, further data, in the form of a larger randomized clinical trial was needed.
The MINT trial was a randomized clinical trial conducted in the United States, Canada, France, Brazil, Australia, and New Zealand which evaluated whether a restrictive transfusion approach (red blood cell transfusion permitted, but not required, for a hemoglobin of less than 8 g/dL and strongly recommended for a hemoglobin level less than 7 g/dL or transfusion when anginal symptoms were not controlled with medications) was superior to a more liberal transfusion strategy (red blood cell transfusion to maintain a hemoglobin concentration ≥ 10 g/dL through hospital discharge or 30 days) in reducing a composite endpoint of all-cause mortality or recurrent MI among individuals with acute myocardial infarction and anemia. The trial enrolled individuals aged 18 years or older with STEMI or NSTEMI (including type 1, 2, 4b, and 4c MI) who were anemic (defined as a hemoglobin of less than 10 g/dL). The trial excluded individuals with uncontrolled bleeding, those planned for cardiac surgery during the index hospitalization, those who declined blood transfusion, and individuals receiving only palliative treatment.
A total of 3504 patients were included in the primary analysis. The average age of the study population was 72 years, approximately 45% were women, and the majority of MI cases were NSTEMI (82%). The mean (± SD) number of red-cell units that were transfused was 0.7±1.6 in the restrictive-strategy group and 2.5 ±2.3 in the liberal-strategy group. The mean hemoglobin level was 1.3 to 1.6 g per deciliter lower in the restrictive-strategy group than in the liberal strategy group on days 1 to 3 after randomization. At 30-days, the primary endpoint of all-cause death or recurrent MI occurred in 16.9% of individuals in the restrictive arm and 14.5% of individuals in the liberal arm (risk ratio modeled with multiple imputation for incomplete follow-up, 1.15; 95% CI 0.99 to 1.34, p=0.07). Secondary endpoints of all-cause death, non-fatal recurrent MI, and a composite of all-cause death/non-fatal recurrent MI/unscheduled coronary revascularization/readmission for ischemic cardiac diagnosis were also not significantly different between the two arms.
In conclusion, a restrictive transfusion strategy was not superior to a liberal transfusion strategy among individuals with acute myocardial infarction and anemia. The investigators noted that while not statistically significant, the point estimates for the primary outcome and secondary outcomes favored a liberal transfusion strategy.
