12: Venous Thromboembolism Flashcards
Venous thromboembolism overview
- Thrombi form in deep calf veins and propagate proximally
- Those involving popliteal vein and more proximal veins (femoral, iliac) are more likely to embolize
- Upper extremity veins in < 10% VTE
- Catheter associated
- More common in athletes
- Paget-Schroetter syndrome (effort-induced)
- Pelvic, renal veins: rare
- 79% of patients with pulmonary embolism (PE) have concurrent lower extremity DVT
Virchow’s Triad
- Theory of VTE pathogenesis:
- Altered blood flow (stasis): hospitalization, extended travel, casting of extremity, pregnancy
- Endothelial injury: trauma, central venous catheter, surgery
- Hypercoagulability (inherited vs. acquired): malignancy, heart failure, nephrotic syndrome, autoimmune dz, oral contraceptives
Inherited VTE risk factors
- Factor V Leiden mutation: slower inactivation of Va by Protein C
- Prothrombin gene mutation: increased prothrombin synthesis
- Protein S deficiency: reduced inactivation of Va
- Protein C deficiency: reduced inactivation of Va
- Antithrombin deficiency: reduced inactivation of IXa, XIa, Xa, thrombin
Acute DVT clinical presentation
- Sx: pain, swelling, erythema in extremity
- PEX: assymetry, warmth, edema, cords (thrombosed superficial veins); findings nonspecific and lack accuracy
- DDx: muscle strain, cellulitis, ruptured Baker’s cyst, post-thrombotic syndrome
Limb ischemia
- 2/2 massive proximal DVT
- Causes severely impaired venous return
- Venous gangrene
- Compartment syndrome
- Aterial compromise
- Rare, but requires immediate therapy
- Referred to as “phlegmasia cerulea dolens”
Wells Score for DVT
C3PO + R2D2
Cancer within 6 months
Calf swelling (3cm difference 10cm below)
Collateral superficial veins (non-varicose)
Pitting edema confined to symptomatic leg
Oedema of the entire leg
Tenderness along deep venous system
Recently bedredden for > 3 days
Recent immobilization of leg (cast, paralysis)
DVT in the past
Diagnosis other than DVT likely (2 points off)
D-dimer assay
- D-dimer: degradation product of cross-linked fibrin
- ↑in pts with VTE (very sensitive), but not specific
- DVT can be ruled out with low clinic suspicion (Wells score < 2) and a negative D-dimer
Diagnosis of DVT
-
Duplex ultrasonography
- Non-invasive test of choice; portable
- Dx made by:
- Abnormal compressibility of vein
- Abnormal Doppler color flow
- Presence of echogenic band
- Sensitivity and specificity > 95%
- Pts w/ high clinical suspicion but negative study should have test repeated in 5-7 days or undergo more testing
- Contrast venography
- Impedance plethysmography
- Magnetic resonance venography
- CT w/ contrast
May-Thurner Syndrome
Rare condition in which compression of the common venous outflow tract of the left lower extremity may cause DVT in the iliofemoral vein.
Initial therapy for DVT
-
Unfractionated heparin (UFH):
- Inactivates thrombin
- IV
- Narrow therapeutic window
- Reversible w/ protamine
- Does not cross placenta
-
Low molecular weight heparin (LMWH):
- Inactivates Xa
- SubQ injection
- ↓recurrent VTE and bleeding compared to UFH
- Caution in specific populations (pregnancy, elderly, renal dz, obese)
-
Fondaparinux
- Newer synthetic agent
- SubQ injection
- Inactivates Xa
- Equally effective as LWMH for VTE
- Similar precautions as LMWH
Transitional therapy for DVT
-
Warfarin
- Inhibits vitamin K-dependent gamma-carboxylation of II, VII, IX, X
- Highly effective at preventing recurrent VTE
- Overlap w/ heparin for 4-5 days
- Treat for at least 3 months
- Interactions with genetics, diet, drugs
- Teratogenic
- **Rivaroxaban **(factor Xa inhibitor)
- **Dabigatran **(direct thrombin inhibitor)
Other options for DVT therapy
-
Catheter directed thrombolysis
- For large clot w/ severe swelling or limb-threatening ischemia (not routine use)
- Improves complete clos lysis and reduced post-thrombotic syndrome, increased bleeding risk
-
IVC filter
- When anticoagulation contraindicated
- Prevent embolism in short-term
- Some brands removeable
- Does not protect against VTE long-term
**Pulmonary Embolism **overview
- Obstruction of pulmonary artery or branches with material originating from elsewhere in the body (mostly DVT, although rarely air, tumor, fat, foreign material)
- Recurrent PE is a common cause of death
Pulmonary embolism pathophysiology
- Thrombi lodge in main pulmonary artery or smaller branches
- Platelets release vasoactive and bronchoactive agents (e.g., serotonin)
- Pulmonary infarction occurs rarely (because dual blood supply of lung)
Hemodynamic compromise in acute pulmonary embolism
- Increased pulmonary vascular resistance
- RV strain and ↓LV preload
- ↓CO, RV ischemia and failure
- CV collapse
Wells Score for PE
Don’t die, tell the team to calculate criteria. (DVT Sx, Dx alt. less likely, tachy, three days immob or thirty days surgery, thrombo Hx, cough up blood, cancer)
