Module 5

DMST 265: Vascular Sonography 1 - Acute Venous Pathophysiology

Course Overview

• Subject: Acute Venous Pathophysiology

• Institution: Southern Alberta Institute of Technology (SAIT)

• School: School of Health and Public Safety

• Term: Winter 88

Learning Outcomes

• Differentiate between acute and chronic venous disease.

• Differentiate the sonographic characteristics of both conditions.

• Perform a sonographic examination of the normal peripheral venous system in a lab setting.

Objectives

1. Thrombus Formation
      - Describe the evolution of thrombus formation and propagation.

2. Signs and Symptoms
      - Name the signs, symptoms, and risk factors of:
        - Acute Deep Venous Thrombosis (DVT)
        - Chronic Venous Insufficiency (CVI)

3. Chronic Venous Insufficiency
      - Discuss factors that lead to CVI.

4. Other Pathologies
      - Explain other pathologies that demonstrate symptoms of venous disease.

5. Treatment
      - Describe treatments for acute and chronic venous diseases.

6. Diagnostic Tests
      - List other medical tests that aid in the diagnosis of venous disease.

7. Sonographic Characteristics
      - Describe sonographic characteristics of acute DVT.

Required Readings

• Kupinski, 3rd Ed.: Chapter 17 (251-270), Chapter 18 (271-281)

• Daigle, 5th Ed.: Chapter 13 (307-331)

Introduction to Acute Venous Disease

• Ultrasound Usage
    - The primary test for ruling out DVT in the lower extremities is ultrasound.
    - Though many DVT cases are diagnosed clinically, ultrasound provides definitive diagnostic value.
    - Failure to treat DVT can lead to complications, such as:
      - Pulmonary Embolus (PE): A life-threatening condition.
      - Chronic Venous Insufficiency (CVI): Further explored in the subsequent module.

Virchow’s Triad

• Understanding Acute Thrombus:
    - Proposed by Rudolph Virchow in 1856, it outlines three risk factors for DVT:
      1. Stasis
      2. Intimal Injury
      3. Hypercoagulability

• Most Common Factor: Venous Stasis, tied to:
    - Immobility due to:
      - Illness
      - Injury
      - Surgery
    - Congestive Heart Failure (CHF)
    - Chronic Obstructive Pulmonary Disease (COPD)
    - Obesity
    - Pregnancy
    - History of Previous DVT

Risk Factors for Hypercoagulability

• Conditions increasing blood clotting likelihood:
    - Cancer
    - Pregnancy
    - Contraceptive Use (birth control pills)
    - Hormonal Replacement Therapy

• Hereditary Factors:
    - Protein C & S deficiencies
    - Factor V Leiden mutation
    - Hyperhomocysteinemia
    - Prothrombin gene mutation (20210)
    - Elevated or deficient plasminogen levels

Clinical Assessment of DVT

Well’s Score

• A clinical scoring system to assess the probability of DVT is based on the following criteria:
    | Criteria | Points |
    |------------------------------------------------|------------|
    | 1. Malignancy | 1 |
    | - Active treatment for cancer | |
    | - Treatment in the last 6 months | |
    | - Palliative care | |
    | 2. Limb Immobilization | 1 |
    | - Paralysis, Paresis, Recent casting | |
    | 3. Patient Immobilization | 1 |
    | - Bed rest > 3 days, Major surgery in last 4 weeks | |
    | 4. Localized Tenderness | 1 |
    | - Along the distribution of the deep venous system | |
    | 5. Entire leg swollen | 1 |
    | 6. Calf swelling | 1 |
    | - More than 3 cm compared to other limb | |
    | - Measured 10 cm below the tibial tuberosity | |
    | 7. Pitting edema | 1 |
    | - Greater in symptomatic leg | |
    | 8. Dilated Collateral Veins | 1 |
    | - Non-varicose veins (dilated collateral veins) | |
    | 9. Alternative Diagnosis | -2 |
    | - Use of history, physical exam, and lab results | |
  

• Scoring Interpretation:
    - Total Points:
      - <0: Low probability     - 1-2: Intermediate probability     - >3: High probability

D-Dimer Assay

• A laboratory test that detects thrombus formation and assesses DVT probability:
    - Negative Result: Indicates low likelihood of DVT (< 500 µg/L).   - Positive Result: Does not specifically indicate DVT (>500 µg/L) but may indicate other conditions such as recent surgery or trauma.

Thrombus Formation Mechanism

• Initial thrombus formation typically starts in:
    - Soleal Sinus
    - Calf Veins
    - Valve Cusps

• Early thrombus development involves aggregations of red blood cells near valve cusps.

• Once stabilized by fibrin, thrombi adhere to the endothelium, and further growth can occur
    - Formation of enlarged pockets is a result of:
      - Fibrinolysis
      - Thrombus retraction
      - Fragmentation

• Treatment includes administering blood thinners to cease propagation while the body naturally lyses the clot.

• Common clinical outcome:
    - Restoration of venous lumen: Intimal thickening is possible, with residual fibrous synechia observed in about 10% of patients.
  

Acute DVT Characteristics

• Thrombus vs. Clot:
    - “Clot” and “thrombus” can be used interchangeably;
    - “Thrombus” is preferred for clots forming within vessels.

• Acute Thrombus: Up to 14 days old; correlates with the onset of clinical symptoms.
    - Appears as:
      - Vein dilation
      - Lack of compressibility confirming thrombus existence.
    - Thrombus may appear anechoic or hypoechoic in comparison to surrounding tissue.
    - Can cause complete or partial occlusion of the vein.

Important Imaging Techniques

• 2D Imaging: Essential for ruling out thrombus presence.

• Colour Doppler Analysis: Identifies blood flow with partial thrombus.

• Compression Tests: Most reliable for ruling out thrombus presence; repeated compression is avoided in cases where thrombus appears to “float”.

Complications of DVT

• Thrombus may lead to collateral formation, providing alternate pathways for venous blood flow.

• Not all thrombus can be visualized; Doppler analysis can help discover thrombus missed in standard scanning protocols.

• Continuous Venous Flow Pattern:
    - Lack of respirophasicity indicates severe underlying issues or compression of veins.

Other Thrombus Types

Sub-Acute Thrombus

• Thrombus aged 1-2 months:
    - Changes include increased echogenicity and decreasing vein diameter due to recanalization.

Chronic Thrombus

• Appearance may be echogenic and “stringy”.

Rare Conditions Related to Venous Thrombosis

May-Thurner Syndrome

• Compression of left Common Iliac Vein (CIV) between External Iliac Artery (CIA) and spine.

• More prevalent in females, presenting with swelling and pain in the left leg.

• Observations include jet during Doppler analysis and altered waveforms compared to the right CFV.

Paget-Schroetter Syndrome (Effort Thrombosis)

• Most common axillo-subclavian thrombosis in healthy, ambulatory individuals.

• Caused by anatomical variations leading to thrombus in axillary/subclavian vein.

Phlegmasia Alba Dolens

• Result of decreased venous drainage due to thrombosis leading to:
    - Extensive edema and “white” discoloration.

Phlegmasia Cerulea Dolens

• Progression from Alba Dolens; significant blood flow obstruction results in potential tissue death.

• Surgical emergency due to risk of gangrene.

Treatment of Acute Venous Disease

Risk Factor Control

• Preventative measures include:
    - Reducing inactivity (e.g., leg elevation, support hoses)
    - Monitoring for hypercoagulability states.

Medical Treatments

1. Anticoagulation Therapy: Lasts 3-6 months using medications like heparin or warfarin. Prevents clot propagation but does not dissolve clots.

2. Thrombolytic Agents: Used directly into the thrombus to dissolve it; higher risks associated, particularly for bleeding.

Surgical Treatments

• Venous Thrombectomy: For severe cases where thrombolysis is ineffective.

• Bypass Grafting: Common in IVC where anticoagulation is not feasible.

• Procedures include balloon venoplasty and stenting for chronic DVTs.

• Caval Filters: Prevent propagation of thrombus to the lungs; analogy of an “upturned umbrella” trapping emboli.

Superficial Thrombophlebitis

• Acute thrombus in superficial veins causing inflammation.

• Diagnosed as a palpable “hard cord” under the skin.

• Ultrasound is crucial to delineate thrombus extent, especially at deep vein confluences.

• Approximately 25% of superficial thrombosis coincides with DVT/PE.

Correlative Testing

• Venography (Venogram): Uses contrast to visualize the venous system; considered the Gold Standard for venous disease.

• Pulmonary Angiogram or CTPA: Best to rule out PE using CT scan with contrast.

• VQ Scans: Nuclear medicine study assessing lung filling and PE presence.

• Isotope Venography: Less common due to delayed tagging of thrombus.

Differential Diagnosis for DVT Symptoms

1. Baker’s Cyst: Dilation of the bursa, usually medial to the knee; can mimic DVT.

2. Hematomas: May cause limb swelling; appears hypoechoic on ultrasound.

3. Edema: Result of fluid overload due to various causes (e.g., CHF, DVT).

4. Infection (Abscess & Cellulitis): May mimic symptoms of DVT.

5. Adenopathy: Enlarged lymph nodes resembling thrombosed veins and causing compression.

6. Tumors: May impede venous return and potentially cause DVT.

7. Popliteal Aneurysm: Presentation with swelling or pain behind the knee; requires Doppler interrogation.