A 62-year-old man with a mechanical heart valve (mitral position) on warfarin presents with acute deep vein thrombosis of the left leg. INR is 1.8. Which is the drug of choice for immediate anticoagulation in this patient?

Explanation

## Drug of Choice for Acute DVT in a Patient on Warfarin **Key Point:** Unfractionated heparin (UFH) is the preferred initial anticoagulant in patients with mechanical heart valves on warfarin who develop acute thrombosis, due to its short half-life, reversibility, and ability to be rapidly discontinued if urgent surgery is needed. ### Why UFH is Preferred in This Clinical Context 1. **Reversibility:** UFH can be rapidly reversed with protamine sulfate if bleeding occurs or if urgent intervention is needed (e.g., valve surgery) 2. **Short half-life:** ~60–90 minutes IV; allows rapid dose adjustment 3. **Mechanical valve consideration:** Patients with mechanical valves are at high thrombotic risk and may require urgent surgical intervention; UFH provides maximum flexibility 4. **Subtherapeutic INR:** The patient's INR of 1.8 is below therapeutic range (2.5–3.5 for mitral mechanical valve); UFH bridges until INR is therapeutic ### Anticoagulant Comparison in Mechanical Valve Thrombosis | Agent | Reversibility | Half-life | Use in Mechanical Valve | Bridging Capability | | --- | --- | --- | --- | --- | | **UFH** | Yes (protamine) | 60–90 min | **Preferred** | Excellent | | LMWH (enoxaparin) | Partial (protamine ~60%) | 4–6 hrs | Avoid (less reversible) | Suboptimal | | Fondaparinux | No | 17–21 hrs | Contraindicated | Poor | | Apixaban (DOAC) | No | 12 hrs | Contraindicated | None | **High-Yield:** In mechanical valve patients, UFH is ALWAYS preferred over LMWH, fondaparinux, or DOACs because of superior reversibility and the ever-present risk of needing emergency valve surgery. ### Management Algorithm ```mermaid flowchart TD A[Mechanical valve on warfarin<br/>+ Acute DVT]:::outcome --> B{INR therapeutic?}:::decision B -->|No| C[Start UFH IV bolus<br/>then infusion]:::action B -->|Yes| D[Continue warfarin,<br/>add UFH bridge]:::action C --> E[Increase warfarin dose<br/>Target INR 2.5-3.5]:::action E --> F[When INR therapeutic<br/>for 24 hrs]:::decision F -->|Yes| G[Stop UFH,<br/>continue warfarin]:::action F -->|No| H[Continue UFH + warfarin]:::action ``` **Clinical Pearl:** Mechanical valve thrombosis is a medical emergency. If anticoagulation fails or the patient becomes hemodynamically unstable, urgent valve replacement or thrombolysis may be needed—UFH's reversibility is critical. **Warning:** LMWH is NOT recommended for mechanical valve patients because: - Partial reversibility with protamine (~60% only) - Unpredictable pharmacokinetics in some patients - Cannot be rapidly discontinued if emergency surgery is needed - DOACs are absolutely contraindicated in mechanical valves (increased thrombotic risk).