Research Highlights:

  • A multinational trial compared examined outcomes in heart attack patients with anemia who received blood transfusions when their hemoglobin concentration levels were at 8 g/dL or 10 g/dL.
  • While results did not reach statistical significance, the findings indicate blood transfusions for anemic patients hospitalized with heart attack to keep the hemoglobin concentration above 10 g/dL may improve patient health.
  • As the largest trial evaluating transfusion thresholds in people after heart attack, the results may help guide decisions by clinicians caring for heart attack patients with anemia.

Embargoed until 10:10 a.m. ET, Saturday, Nov. 11, 2023

PHILADELPHIA, Nov. 11, 2023 — While the indications for red blood cell transfusion are controversial for people hospitalized with a heart attack, a randomized controlled trial of more than 3,500 people suggests there may be benefits to an expanded transfusion approach, according to late-breaking science presented today at the American Heart Association’s Scientific Sessions 2023. The meeting, Nov. 11-13, in Philadelphia, is a premier global exchange of the latest scientific advancements, research and evidence-based clinical practice updates in cardiovascular science. The full manuscript is also simultaneously published today in The New England Journal of Medicine.

Previous studies on transfusion strategies for people hospitalized with heart attack have yielded conflicting results. Doctors thought giving more blood transfusions would increase the amount of oxygen for the heart and improve outcomes. However, giving more blood transfusions may increase the risk of fluid overload and rare infections. This uncertainty in when to transfuse heart attack patients led to this trial called Myocardial Ischemia and Transfusion (MINT).

“Low red blood count or anemia is common among people hospitalized with heart attack,” said study author Jeffrey L. Carson, M.D., who is provost and distinguished professor of medicine at Rutgers Robert Wood Johnson Medical School in New Brunswick, New Jersey, and holds the Richard C. Reynolds chair in general internal medicine. “We believe our results suggest a more liberal transfusion approach may be beneficial for these patients without significant risk.”

In the MINT trial, anemia was defined as a hemoglobin concentration of less than 10 g/dL. Participants were randomly allocated to a restrictive or a liberal transfusion strategy. In the liberal transfusion strategy, red blood cells were transfused to maintain the hemoglobin at or above 10 g/dL through hospital discharge or 30 days. In the restrictive transfusion strategy, transfusion was permitted only when the hemoglobin concentration was less than 8 g/dL and strongly recommended when the hemoglobin concentration was less than 7 g/dL or for cardiac symptoms not controlled with medications.

The analysis found:

  •  295 (16.9%) of the 1,749 participants in the restrictive transfusion trial pool experienced a recurrent heart attack or death compared to 255 (14.5%) among 1,755 participants in the liberal transfusion pool.
  • Cardiac death was more common in people treated with a restrictive transfusion strategy (5.5%) compared to death among those treated in the liberal strategy (3.2%).
  • Heart failure and other 30-day clinical outcomes were similar in both groups, suggesting there is no undue risk to more liberal transfusions.

“The study results require a nuanced interpretation. While the trial did not produce a statistically significant difference between the two transfusion strategies for the primary outcome, the results suggest the possibility of liberal transfusion benefits without undue risk,” Carson said. “The MINT results suggest a liberal transfusion strategy may be the most prudent approach for patients with heart attack and anemia.”

Trial background and details:

  • The randomized controlled trial enrolled 3,506 participants from 144 hospitals in the United States, Canada, France, Brazil, New Zealand and Australia between April 2017 and April 2023.
  • All participants (average age 72 years; 45% women; 55% men) had heart attack and hemoglobin concentration levels less than 10 g/dL. Normal hemoglobin concentration is 12-13 g/dL, Carson said.
  • Many participants also had other health conditions, including a history of heart attack (33%), heart failure (30%) diabetes (54%) and kidney disease (46%).
  • The primary trial endpoint was the composite of all-cause death and recurrent heart attack through 30 days following trial randomization.
  • Secondary outcomes included the individual components of the primary outcome, and the composite of all-cause death, heart attack, unscheduled coronary revascularization due to recurrent heart symptoms, or readmission to the hospital for a heart-related diagnosis within 30 days. Cause of death was classified as cardiac, non-cardiac or undetermined. Other trial outcomes included heart failure and infection.

MINT results should be interpreted with caution because the analyses were not adjusted for multiple statistical tests, Carson said. Other limitations include that treating clinicians knew which strategy participants were assigned to, and not all participants were discharged with hemoglobin concentration levels greater than 10 g/dL in the liberal transfusion group. This was frequently due to clinical discretion, such as concerns about fluid overload and timing of hospital discharge. In addition, recurrent myocardial infarction was the only outcome confirmed by an independent committee, and hence, the cause of death was classified by the research team at the study hospital.

“Future research is needed to further resolve the controversy around transfusion decisions for people with anemia and heart attack,” Carson noted.

Co-authors, disclosures and funding sources are listed in the abstract.

Statements and conclusions of studies that are presented at the American Heart Association’s scientific meetings are solely those of the study authors and do not necessarily reflect the Association’s policy or position. The Association makes no representation or guarantee as to their accuracy or reliability. Abstracts presented at the Association’s scientific meetings are not peer-reviewed, rather, they are curated by independent review panels and are considered based on the potential to add to the diversity of scientific issues and views discussed at the meeting. The findings are considered preliminary until published as a full manuscript in a peer-reviewed scientific journal.

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