MINT Trial

Restrictive or Liberal Transfusion Strategy in Myocardial Infarction and Anaemia

What was it?

Multicenter, open-label, randomized controlled trial (Myocardial Ischemia and Transfusion, MINT) evaluating a restrictive (hemoglobin trigger ≤7-8 g/dL) versus a liberal (hemoglobin trigger <10 g/dL) red blood cell transfusion strategy in patients with acute myocardial infarction (MI) and anemia.

The Devil in the Details!

• 3,504 patients analyzed
  • 1,749 restrictive
  • 1,755 liberal
• Multiple centers in the U.S., Canada, France, Brazil, New Zealand, and Australia.
• Patients with acute MI (type 1 or 2) and hemoglobin <10 g/dL were randomized to either
  • Restrictive transfusion strategy (transfusion if hemoglobin ≤7-8 g/dL, targeting 8-10 g/dL)
  • Liberal strategy (transfusion if hemoglobin <10 g/dL, targeting ≥10 g/dL).
• Primary outcome: Composite of recurrent MI or all-cause death at 30 days.
• Secondary outcomes: Individual components of the primary outcome (death, recurrent MI), major adverse cardiovascular events (MACE: death, MI, stroke, or unscheduled revascularization), and other tertiary endpoints like heart failure.
• Mean number of red blood cell units transfused: 0.7 ± 1.6 (restrictive) vs. 2.5 ± 2.3 (liberal).

The Results!

• Primary outcome (recurrent MI or death at 30 days) relative risk [RR] 1.15, 95% (CI 0.99-1.34, p=0.07), indicating no significant difference:
  • 16.9% in the restrictive group
  • 14.5% in the liberal group
• All-cause death:
  • 9.3% (restrictive)
  • 8.2% (liberal) (RR 1.13, 95% CI 0.90-1.41).
• Recurrent MI:
  • 8.5% (restrictive)
  • 7.2% (liberal) (RR 1.19, 95% CI 0.94-1.51).
• A prespecified analysis showed a potential trend toward harm with the restrictive strategy in type 1 MI (RR 1.32, 95% CI 1.04-1.67) but not in type 2 MI (RR 1.05, 95% CI 0.85-1.29).
• In patients with chronic kidney disease (CKD) and eGFR <30 mL/min/1.73 m² (not on dialysis), the restrictive strategy was associated with a higher risk of death or recurrent MI (risk difference 5.8%, 95% CI 0.4%-11.2%).
• No significant differences in heart failure, stroke, or other secondary outcomes. Potential harms of the restrictive strategy could not be excluded.

They concluded

Liberal transfusion strategy did not significantly reduce the risk of recurrent MI or death at 30 days compared to a restrictive strategy in patients with acute MI and anemia. However, the data suggest a potential trend toward benefit with a liberal strategy, particularly in type 1 MI, and potential harm with a restrictive strategy in certain subgroups (e.g., CKD patients). Further studies are needed to confirm these findings.

Gripe Point Summary!

Further gripes here

The MINT trial provides valuable insights into transfusion strategies for MI patients with anemia, but:

• Open-label design introduces potential bias in clinical decision-making.
• Non-significant primary outcome limits definitive conclusions.
• Heterogeneity in MI types (type 1 vs. type 2) complicates interpretation.
• Short follow-up (30 days) misses long-term outcomes.
• Potential harm in subgroups (e.g., CKD, type 1 MI) not fully explored.
• Variability in transfusion triggers (7-8 g/dL in restrictive arm) may affect consistency.
• Lack of blinding in transfusion administration could influence outcomes.
• Limited generalizability to non-hospitalized or less severe anemia cases.

Our Summary

In patients with acute MI and anemia, a liberal transfusion strategy (hemoglobin <10 g/dL) did not significantly reduce the risk of recurrent MI or death at 30 days compared to a restrictive strategy (hemoglobin ≤7-8 g/dL). However, trends suggest potential benefits of the liberal approach, especially in type 1 MI and CKD patients, with possible harm from the restrictive strategy in specific subgroups. The trial’s large sample size and multicenter design are strengths, but larger trials with longer follow-up are needed to clarify optimal transfusion thresholds.

Who’s worked on this before?

• Ducrocq G, et al. Effect of a restrictive vs liberal blood transfusion strategy on major cardiovascular events among patients with acute myocardial infarction and anemia: the REALITY randomized clinical trial. JAMA 2021;325:552-560.
• Cooper HA, et al. Conservative versus liberal red cell transfusion in acute myocardial infarction (the CRIT Randomized Pilot Study). Am J Cardiol 2011;108:1108-1111.
• Carson JL, et al. Liberal versus restrictive transfusion thresholds for patients with symptomatic coronary artery disease. Am Heart J 2013;165:964.e1-971.e1.
• Carson JL, et al. Transfusion thresholds for guiding red blood cell transfusion. Cochrane Database Syst Rev 2021;12:CD002042.
• Gonzalez-Juanatey JR, et al. One-year major cardiovascular events after restrictive versus liberal blood transfusion strategy in patients with acute myocardial infarction and anemia: the REALITY randomized trial. Circulation 2022;145:486-488.

Further gripes

• Open-label design: The lack of blinding in transfusion administration could introduce bias, as clinicians’ knowledge of the assigned strategy might influence other treatments or outcome assessments.
• Non-significant primary outcome: The p-value of 0.07 for the primary outcome suggests a trend but not statistical significance, weakening the ability to draw firm conclusions about the superiority of either strategy.
• Heterogeneity in MI types: Type 1 and type 2 MI have different pathophysiologies, and the trial’s mixed population may obscure strategy-specific effects. The prespecified analysis showing potential harm in type 1 MI needs further exploration.
• Short follow-up period: The 30-day follow-up limits insights into long-term outcomes, such as 6-month or 1-year mortality, where a meta-analysis suggested increased all-cause mortality with a restrictive strategy at 6 months.
• Subgroup concerns: The higher risk of adverse outcomes in CKD patients (eGFR <30 mL/min/1.73 m²) with a restrictive strategy suggests potential harm in specific populations, but the trial was not powered to confirm these findings.
• Variable transfusion triggers: The restrictive arm allowed a hemoglobin trigger range of 7-8 g/dL, which introduces variability in clinical practice and could dilute<<<<<<< affect consistency of results.
• Limited generalizability: The trial focused on hospitalized patients with hemoglobin <10 g/dL, potentially excluding milder cases of anemia or outpatient settings, limiting broader applicability.
• Lack of data on non-transfusion interventions: The trial did not report on concurrent treatments (e.g., antiplatelet therapy, beta-blockers) that could influence outcomes and confound results.
• No quality-of-life outcomes: Unlike the clonidine trial, no quality-of-life measures were reported, which could provide insight into patient-centered outcomes beyond clinical events.

CCN’s Reflection

The MINT trial is a robust effort to address a critical question in the management of acute MI with anemia, offering the largest dataset to date with 3,504 patients. Its multicenter design and pragmatic approach enhance its clinical relevance. However, the open-label design, non-significant primary outcome, and short follow-up period temper its impact. The suggestion of potential harm from a restrictive strategy in type 1 MI and CKD patients is concerning but inconclusive, highlighting the need for further research. While the trial moves the needle toward questioning restrictive transfusion practices, it’s not a game-changer yet. Larger, blinded trials with longer follow-up and subgroup-specific analyses are essential to refine transfusion strategies in this complex population. Stay tuned for more clarity on this high-stakes dilemma

Review by JW.