PDF: RE-ALIGN
(2013)Objective
To evaluate the safety and efficacy of dabigatran as an alternative to warfarin in patients with mechanical heart valves for the prevention of thromboembolic events.
Study Summary
• Dabigatran was associated with increased rates of thromboembolic and bleeding events in patients with mechanical heart valves, leading to early termination of the trial.
Intervention
Patients with recent or remote mechanical aortic or mitral valve replacement were randomized to receive dabigatran (150–300 mg twice daily) or dose-adjusted warfarin, with the goal of comparing thromboembolic and bleeding outcomes.
Inclusion Criteria
Patients aged ≥18 years with mechanical heart valve prostheses in the aortic or mitral position, either within 7 days of surgery (early cohort) or after 3 months post-surgery (late cohort).
Study Design
Arms: Dabigatran vs. Warfarin (INR 2.0–3.5 target)
Patients per Arm: Dabigatran: 126, Warfarin: 40
Outcome
• Thromboembolic events: 9 (7 strokes, 1 TIA, 1 MI) in dabigatran group vs. none in warfarin group; • Major bleeding: 7 in dabigatran group vs. 2 in warfarin; • All strokes and bleeding events occurred in the dabigatran arm; • Trial was terminated early due to excess events in dabigatran group; • No thromboembolic or major bleeding events in warfarin group.
Bottom Line
The use of dabigatran in patients with mechanical heart valves was associated with increased rates of both thromboembolic events (stroke) and bleeding complications compared to warfarin. The trial was terminated prematurely, demonstrating that dabigatran should not be used in this patient population.
Major Points
- RE-ALIGN is the definitive safety trial establishing that DOACs should NEVER be used in mechanical heart valve patients — a critical 'do not use' landmark that every clinician prescribing DOACs must know.
- Phase 2 dose-validation study terminated prematurely by DSMB due to excess of BOTH thromboembolic AND bleeding events with dabigatran — the worst possible combination of outcomes (more clots AND more bleeding simultaneously).
- Stroke: 5% (9/168) dabigatran vs 0% (0/84) warfarin — all thromboembolic events occurred in the dabigatran group. Additionally, 5 patients had asymptomatic valve thrombosis detected on echocardiography.
- Bleeding paradox: despite inadequate anticoagulation for valve thromboprevention, dabigatran caused MORE bleeding: any bleeding 27% vs 12% (HR 2.45, p=0.01); major bleeding 4% vs 2%. This paradox reflects that valve thrombosis and bleeding operate through different mechanisms.
- 252 patients across 39 centers in 10 countries. Two populations enrolled: Population A (79% of cohort) = recent mechanical valve surgery within 7 days; Population B = mechanical mitral valve >3 months post-surgery.
- Most thromboembolic events occurred in Population A (early post-operative) — suggesting dabigatran was particularly dangerous in the immediate post-surgical period when the valve-blood interface is most thrombogenic and the foreign surface requires consistent contact pathway inhibition.
- Mechanism of failure: mechanical valves generate thrombin via the CONTACT PATHWAY (factor XII, XI) on foreign surfaces, not the tissue factor pathway that DOACs target. Warfarin inhibits all vitamin K-dependent factors including the contact pathway, while dabigatran only inhibits free thrombin — insufficient for the massive thrombin generation on prosthetic surfaces.
- Dabigatran dosing was based on plasma trough levels (target ≥50 ng/mL) with doses up to 300 mg BID — even at these high doses, anticoagulation was inadequate for mechanical valves while simultaneously causing bleeding through systemic over-anticoagulation.
- Led to FDA black box warning (2012) and EMA contraindication for dabigatran in mechanical heart valves. Subsequently, ALL DOACs carry a contraindication for mechanical valves — a class-level prohibition based primarily on this single trial.
- The only randomized trial of DOACs in mechanical valves — no subsequent trial has been attempted because RE-ALIGN conclusively demonstrated harm. This makes mechanical heart valves the one absolute contraindication common to ALL DOACs.
Study Design
- Study Type
- Prospective, randomized, phase 2, open-label trial with blinded end-point adjudication.
- Randomization
- Yes
- Blinding
- Open-label with blinded endpoint adjudication.
- Sample Size
- 252
- Follow-up
- Planned for 12 weeks with an extension phase; terminated early.
- Centers
- 39
- Countries
- 10 countries, including Canada and nations in Western and Central Europe.
Primary Outcome
Definition: The primary outcome was the trough plasma level of dabigatran (pharmacokinetic endpoint). The key clinical efficacy outcome was a composite of death, stroke, systemic embolism, or myocardial infarction.
| Control | Intervention | HR/OR | P-value |
|---|---|---|---|
| 2% (2/84) | 8% (13/168) | 3.37 (0.76-14.95) | 0.11 |
Limitations & Criticisms
- Open-label design — though outcomes were adjudicated blindly, awareness of treatment assignment could have influenced monitoring intensity and clinical decision-making.
- Small sample size (252 patients) — the trial was never intended to be a definitive outcomes trial; it was a phase 2 PK/dose-validation study that happened to detect a clear harm signal.
- Only tested dabigatran (direct thrombin inhibitor) — cannot directly extrapolate to factor Xa inhibitors (rivaroxaban, apixaban, edoxaban), though the mechanism of failure (insufficient contact pathway inhibition) is shared by all DOACs.
- Population A (79%) dominated the results — most events occurred early post-op. It remains unclear whether chronic, stable mechanical valve patients might tolerate DOACs differently, though Population B also showed excess events.
- Dabigatran trough-guided dosing was novel and unvalidated — the target of ≥50 ng/mL was extrapolated from AF data and may have been inappropriate for the higher thrombogenic burden of mechanical valves.
- No study of factor Xa inhibitors in mechanical valves has been attempted since RE-ALIGN — the blanket contraindication for all DOACs is an extrapolation from a single dabigatran trial, though mechanistically justified.
- Very short planned follow-up (12 weeks) — even within this brief period, the harm was evident, suggesting the signal would only worsen with longer exposure.
- Industry-sponsored (Boehringer Ingelheim, manufacturer of dabigatran/Pradaxa) — to their credit, the manufacturer published the negative results promptly and updated the label with a contraindication.
- Does not address bioprosthetic valves — subsequent trials (RIVER, DAWA) have explored DOACs in bioprosthetic valves with more favorable results, highlighting the mechanical vs bioprosthetic distinction.
Citation
N Engl J Med 2013;369:1206-14.