A 58-year-old woman with atrial fibrillation (CHA₂DS₂-VASc score 4) and a mechanical mitral valve replacement requires anticoagulation. Which of the following is the drug of choice for stroke prevention in this patient?

Explanation

## Anticoagulation in Atrial Fibrillation with Mechanical Heart Valve **Key Point:** Warfarin is the ONLY anticoagulant approved and recommended for patients with mechanical heart valves. DOACs (direct oral anticoagulants) are contraindicated in mechanical valve disease due to increased thrombotic risk. ### Why Warfarin is Mandatory in Mechanical Valves 1. **Mechanical valve thrombosis risk**: Mechanical valves have a high thrombotic potential (up to 4% per year without anticoagulation) 2. **DOAC inadequacy**: Dabigatran, apixaban, and rivaroxaban have NOT been studied or approved for mechanical valve disease and are associated with increased valve thrombosis and stroke 3. **Warfarin evidence**: Decades of clinical experience and RCTs demonstrate warfarin's efficacy in preventing mechanical valve thrombosis 4. **INR target**: For mechanical mitral valves, target INR is 2.5–3.5 (higher than for AF alone, which is 2–3) ### Comparison: Warfarin vs. DOACs in AF | Feature | Warfarin | DOACs (Dabigatran, Apixaban, Rivaroxaban) | |---------|----------|-------------------------------------------| | **Mechanical valve AF** | ✓ Indicated | ✗ Contraindicated | | **Bioprosthetic valve AF** | Acceptable | Acceptable (if no other indications for warfarin) | | **Native AF (no valve)** | Acceptable | Preferred (if no contraindications) | | **INR monitoring** | Required | Not required | | **Dietary interactions** | Yes (vitamin K) | No | | **Drug interactions** | Moderate | Fewer | **High-Yield:** Mechanical heart valves are an absolute contraindication to DOACs. Warfarin is the only anticoagulant with proven efficacy in mechanical valve disease. This is a high-yield, frequently tested concept in NEET PG. **Clinical Pearl:** Bioprosthetic valves (especially if >3 months post-implant) can be anticoagulated with either warfarin or DOACs, but mechanical valves require warfarin exclusively. **Mnemonic:** **MECHANICAL = WARFARIN** — A simple memory aid: mechanical valves mandate warfarin. DOACs are only for native AF or bioprosthetic valves. **Warning:** Do NOT prescribe DOACs to patients with mechanical valves, even if they have AF. This is a common exam trap and a critical patient safety issue.