A 58-year-old man with newly diagnosed atrial fibrillation presents with acute left leg swelling and pain. Doppler ultrasound confirms left deep vein thrombosis (DVT). PT is 12 s (normal 12–14 s), aPTT is 28 s (normal 24–36 s), and fibrinogen is 280 mg/dL (normal 200–400 mg/dL). What is the most appropriate immediate next step in management?

Explanation

## Clinical Scenario Analysis This patient has: - **Acute DVT** (confirmed on Doppler) - **Normal coagulation profile** (PT, aPTT, fibrinogen all within range) - New-onset atrial fibrillation (thromboembolism risk) - No contraindications to anticoagulation evident ## Coagulation Status Interpretation **Key Point:** All coagulation parameters are **normal**. There is **no coagulation defect** to correct. | Parameter | Value | Normal Range | Interpretation | |-----------|-------|--------------|----------------| | PT | 12 s | 12–14 s | Normal | | aPTT | 28 s | 24–36 s | Normal | | Fibrinogen | 280 mg/dL | 200–400 mg/dL | Normal | ## Management Algorithm for Acute DVT ```mermaid flowchart TD A[Acute DVT confirmed]:::outcome A --> B{Coagulation normal?}:::decision B -->|Yes| C[Proceed with anticoagulation]:::action B -->|No| D[Correct defect first<br/>FFP, vitamin K, etc.]:::action C --> E{UFH or LMWH?}:::decision E -->|Proximal DVT,<br/>high bleeding risk| F[UFH bolus + infusion<br/>aPTT monitoring]:::action E -->|Distal DVT,<br/>standard risk| G[LMWH or fondaparinux<br/>SC daily]:::action F --> H[Transition to warfarin<br/>or DOAC at day 5–7]:::action G --> H ``` ## Why This Answer Is Correct **High-Yield:** In acute DVT with **normal coagulation**, immediate anticoagulation is indicated to prevent PE and thrombus propagation. **Clinical Pearl:** UFH is preferred in: - Proximal DVT (high PE risk) - Renal impairment (eGFR < 30 mL/min) - Potential need for urgent surgery/IVC filter - Hemodynamic instability **Dosing & Monitoring:** 1. **Bolus:** 80 U/kg IV (typically 5,000–10,000 U) 2. **Infusion:** 18 U/kg/hr (typically 1,000–2,000 U/hr) 3. **aPTT target:** 1.5–2.5× baseline (60–100 s) or 50–70 s (lab-dependent) 4. **Recheck aPTT:** 6 hours after bolus, then daily once therapeutic 5. **Transition:** At day 5–7, overlap with warfarin (target INR 2–3) or switch to DOAC **Mnemonic:** **UFH-STAT** = UFH when **S**urgery imminent, **T**ransition needed, **A**cute renal failure, **T**hrombocytopenia risk. ## Why Other Options Are Wrong | Option | Why Incorrect | |--------|---------------| | **FFP administration** | FFP is used to **correct coagulopathy** (low fibrinogen, PT/aPTT prolongation). This patient has **normal coagulation**—FFP is unnecessary and delays definitive anticoagulation. | | **CTPA before anticoagulation** | While PE screening is reasonable in DVT, it should **not delay anticoagulation** in a patient with confirmed proximal DVT and normal coagulation. Anticoagulation is started immediately; CTPA can be obtained concurrently if clinical suspicion is high. | | **Warfarin monotherapy** | Warfarin has a **delayed onset** (3–5 days for therapeutic INR) and causes transient **hypercoagulability** (protein C depletion before factors II, IX, X). It is **never used as monotherapy** for acute DVT; UFH or LMWH must be given first, with warfarin overlap. | ## Transition & Duration **Key Point:** After 5–7 days of UFH with therapeutic aPTT, transition to: - **Warfarin** (INR 2–3, overlap 2–3 days) for long-term (≥3 months in AF-related thromboembolism) - **DOAC** (apixaban, rivaroxaban, dabigatran, edoxaban) — increasingly preferred; some can be started immediately **High-Yield:** Duration of anticoagulation in AF-related DVT is **indefinite** (or until AF is reversed or rate-controlled), not 3 months.