Study rationale, design, and findings
Anemia, or low RBC count, is common in patients with MI, Dr. Carson noted. A normal hemoglobin is 13 g/dL in men and 12 g/dL in women. Administering a packed RBC transfusion only when a patient’s hemoglobin falls below 7 or 8 g/dL has been widely adopted, but it is unclear if patients with acute MI may benefit from a higher hemoglobin level.
“Blood transfusion may decrease ischemic injury by improving oxygen delivery to myocardial tissues and reduce the risk of reinfarction or death,” the researchers wrote. “Alternatively, administering more blood could result in more frequent heart failure from fluid overload, infection from immunosuppression, thrombosis from higher viscosity, and inflammation.”
From 2017 to 2023, investigators enrolled 3,504 adults aged 18 and older at 144 sites in the United States (2,157 patients), Canada (885), France (323), Brazil (105), New Zealand (25), and Australia (9).
The participants had ST-elevation or non–ST-elevation MI and hemoglobin less than 10 g/dL within 24 hours. Patients with type 1 (atherosclerotic plaque disruption), type 2 (supply-demand mismatch without atherothrombotic plaque disruption), type 4b, or type 4c MI were eligible.
They were randomly assigned to receive:
- A ‘restrictive’ transfusion strategy (1,749 patients): Transfusion was permitted but not required when a patient’s hemoglobin was less than 8 g/dL and was strongly recommended when it was less than 7 g/dL or when anginal symptoms were not controlled with medications.
- A ‘liberal’ transfusion strategy (1,755 patients): One unit of RBCs was administered after randomization, and RBCs were transfused to maintain hemoglobin 10 g/dL or higher until hospital discharge or 30 days.
The patients had a mean age of 72 years and 46% were women. More than three-quarters (78%) were White and 14% were Black. They had frequent coexisting illnesses, about a third had a history of MI, percutaneous coronary intervention, or heart failure; 14% were on a ventilator and 12% had renal dialysis. The median duration of hospitalization was 5 days in the two groups.
At baseline, the mean hemoglobin was 8.6 g/dL in both groups. At days 1, 2, and 3, the mean hemoglobin was 8.8, 8.9, and 8.9 g/dL, respectively, in the restrictive transfusion group, and 10.1, 10.4, and 10.5 g/dL, respectively, in the liberal transfusion group.
The mean number of transfused blood units was 0.7 units in the restrictive strategy group and 2.5 units in the liberal strategy group, roughly a 3.5-fold difference.
After adjustment for site and incomplete follow-up in 57 patients (20 with the restrictive strategy and 37 with the liberal strategy), the estimated RR for the primary outcome in the restrictive group versus the liberal group was 1.15 (P = .07).
“We observed that the 95% confidence interval contains values that suggest a clinical benefit for the liberal transfusion strategy and does not include values that suggest a benefit for the more restrictive transfusion strategy,” the researchers wrote. Heart failure and other safety outcomes were comparable in the two groups.
The trial was supported by grants from the National Heart, Lung, and Blood Institute and by the Canadian Blood Services and Canadian Institutes of Health Research Institute of Circulatory and Respiratory Health. Dr. Carson, Dr. Leon, Dr. Gibson, and Dr. Mazer reported no relevant financial relationships.
A version of this article first appeared on Medscape.com.