Deep vein thrombosis (DVT) is a potentially life-threatening condition that occurs when a blood clot forms in the deep veins, most commonly in the legs. While often silent in its early stages, DVT can lead to pulmonary embolism, a serious complication that requires immediate medical intervention. Understanding the root causes of DVT is critical for prevention, diagnosis, and prompt treatment.
To help students, clinicians, and the general public remember the key risk factors associated with DVT, the mnemonic “THROMBOSIS” offers a simple yet effective guide:
- T – Trauma
- H – Hormones (e.g., oral contraceptives)
- R – Road traffic accidents
- O – Operations (e.g., cholecystectomy)
- M – Malignancy
- B – Blood disorders (e.g., polycythemia)
- O – Obesity/old age
- S – Serious illness
- I – Immobilization
- S – Splenectomy
Let’s dive into each of these etiological factors in detail and understand their pathophysiological roles in promoting thrombus formation in deep veins.
What is Deep Vein Thrombosis (DVT)?
Deep vein thrombosis occurs when a blood clot (thrombus) forms in the deep veins of the body, most often in the lower extremities (legs, thighs, or pelvis). The clot obstructs blood flow and may partially or completely block venous return to the heart.
Key Features of DVT:
- Pain or cramping in the leg
- Swelling, especially in one limb
- Redness or discoloration
- Warmth over the affected area
DVT is a part of venous thromboembolism (VTE), a condition that includes both DVT and pulmonary embolism (PE). Timely identification of etiological factors is essential for early intervention.
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The “THROMBOSIS” Mnemonic: Etiological Breakdown
Each letter in the mnemonic corresponds to a significant risk factor for DVT. Let’s explore each in detail.
T – Trauma
Trauma, particularly to the lower limbs or pelvis, is a classic predisposing factor for DVT. This includes:
- Fractures
- Surgical trauma
- Crush injuries
How it Causes DVT:
- Endothelial damage triggers the coagulation cascade
- Venous stasis due to pain-related immobility
- Inflammatory response promotes hypercoagulability
Trauma disrupts Virchow’s triad—especially endothelial injury and stasis, two primary triggers for thrombus formation.
H – Hormones (Oral Contraceptive Pills - OCPs)
Hormonal therapies, particularly estrogen-based contraceptives and hormone replacement therapy (HRT), increase the risk of venous thrombosis.
Mechanisms:
- Estrogen increases clotting factors (Factor VII, VIII, fibrinogen)
- Reduces antithrombin III
- Promotes venous stasis via fluid retention
Women who smoke, are obese, or have a family history of DVT are at exponentially increased risk when on OCPs.
R – Road Traffic Accidents
Motor vehicle accidents often result in:
- Prolonged immobilization
- Long bone fractures
- Need for emergency surgeries
All of these events create a hypercoagulable state, especially when ICU care is involved.
Special Considerations:
- DVT risk may persist weeks after discharge
- Patients should be evaluated for thromboprophylaxis
O – Operations (Cholecystectomy and Others)
Surgical procedures are well-known DVT triggers, especially:
- Abdominal surgeries (e.g., cholecystectomy)
- Orthopedic surgeries
- Pelvic operations
Surgical Risks Include:
- Venous stasis during long procedures
- Tissue injury promoting thrombogenesis
- Postoperative immobility
Routine administration of anticoagulants and compression devices during and after surgery is key for DVT prevention.
M – Malignancy
Cancer is a prothrombotic condition due to the release of:
- Tumor-derived procoagulants
- Cytokines that promote inflammation
- Activation of platelets and clotting cascade
High-Risk Cancers for DVT:
- Pancreatic
- Lung
- Gastrointestinal
- Ovarian
Trousseau’s syndrome describes migratory thrombophlebitis seen in malignancy-associated DVT.
B – Blood Disorders (e.g., Polycythemia)
Polycythemia vera, thrombophilia, and other coagulation disorders significantly increase DVT risk.
Inherited Conditions:
- Factor V Leiden
- Protein C or S deficiency
- Antithrombin III deficiency
Acquired Conditions:
- Antiphospholipid syndrome
- Myeloproliferative disorders
A complete hypercoagulable workup is essential in young patients with unexplained DVT.
O – Obesity/Old Age
Obesity and aging are two of the most underappreciated yet powerful contributors to venous thrombosis.
Obesity Mechanisms:
- Increased abdominal pressure reduces venous return
- Systemic inflammation promotes hypercoagulability
- Sedentary lifestyle increases venous stasis
Old Age Factors:
- Decline in mobility
- Vessel wall changes
- Comorbidities such as heart failure or cancer
Prophylaxis in elderly surgical patients is critical.
S – Serious Illness
Conditions that require hospitalization or ICU stay (like pneumonia, sepsis, or heart failure) often induce a prothrombotic state due to:
- Cytokine storm
- Immobility
- Use of central lines or catheters
Severe infections (like COVID-19) have also been linked to high rates of thrombotic complications.
I – Immobilization
Prolonged immobility leads to venous pooling, decreased shear stress, and eventual thrombus formation.
Common Scenarios:
- Long-haul flights (>6 hours)
- Prolonged bed rest after surgery or stroke
- Plaster casting for fractures
This is the most modifiable risk factor for DVT. Early ambulation and leg exercises can dramatically reduce the risk.
S – Splenectomy
Removal of the spleen increases susceptibility to thrombosis, particularly in the portal and splenic veins.
Why?
- Loss of spleen alters platelet dynamics
- Increased platelet count post-splenectomy
- Possible activation of coagulation cascade
This complication is more common in patients with hematological diseases like thalassemia or myelofibrosis.
Virchow’s Triad and DVT
The mnemonic “THROMBOSIS” aligns well with Virchow’s Triad, the three foundational mechanisms behind thrombus formation:
| Component | Examples |
|---|---|
| Endothelial Injury | Trauma, surgery, IV lines |
| Hypercoagulability | Hormones, cancer, blood disorders |
| Venous Stasis | Immobility, obesity, long flights |
Clinical Signs and Symptoms of DVT
| Symptom | Description |
|---|---|
| Leg swelling | Usually unilateral |
| Pain | Especially in calf or thigh |
| Warmth | Localized to affected area |
| Redness | Erythema over the clot |
| Dilated superficial veins | Due to obstruction of deep veins |
| Positive Homans’ sign | Calf pain on dorsiflexion (not specific) |
Diagnostic Approach
1. D-dimer
Elevated in most DVT cases, though not specific.
2. Compression Ultrasound
First-line imaging for suspected DVT.
3. Venography
Gold standard but rarely used due to invasiveness.
4. CT/MR Venography
Used in complex or pelvic DVTs.
DVT Prevention Strategies
| Intervention | Target Mechanism |
|---|---|
| Compression stockings | Reduce venous stasis |
| Early ambulation | Improves circulation |
| Anticoagulants (e.g., LMWH) | Interrupt coagulation cascade |
| Intermittent pneumatic compression | Mechanical prevention in ICU |
| Hydration | Reduces blood viscosity |
| Avoid OCPs in high-risk women | Eliminates hormonal risk |
Complications of Untreated DVT
| Complication | Description |
|---|---|
| Pulmonary embolism | Clot travels to lungs; life-threatening |
| Post-thrombotic syndrome | Chronic pain, swelling, ulcers |
| Recurrent DVT | Especially in inherited thrombophilia |
| Venous insufficiency | Valve damage leads to varicosities |
Frequently Asked Questions (FAQs)
What is the most common site for DVT?
The popliteal and femoral veins of the lower leg are most commonly affected.
Can DVT resolve on its own?
Some small clots may resolve, but most require medical treatment to prevent embolism.
Who is most at risk?
- Post-surgical patients
- Cancer patients
- Obese and sedentary individuals
- Elderly with comorbidities
Is walking good for DVT?
Walking is good for prevention, but suspected DVT should be evaluated first before encouraging movement.
How long is treatment for DVT?
Usually 3–6 months, but lifelong anticoagulation may be needed in recurrent or inherited cases.
Summary Table: “THROMBOSIS” Mnemonic for DVT Causes
| Letter | Cause | Pathophysiology |
|---|---|---|
| T | Trauma | Endothelial damage, immobility |
| H | Hormones | Increased clotting factors |
| R | Road traffic accidents | Immobilization, surgery |
| O | Operations | Stasis, inflammation |
| M | Malignancy | Tumor-related coagulation |
| B | Blood disorders | Hypercoagulable state |
| O | Obesity/Old age | Reduced mobility, systemic inflammation |
| S | Serious illness | Cytokine-driven hypercoagulation |
| I | Immobilization | Venous pooling |
| S | Splenectomy | Altered platelet dynamics |
Final Thoughts
Deep vein thrombosis is a silent yet dangerous condition, and recognizing its causes is key to prevention. The “THROMBOSIS” mnemonic provides a concise and powerful way to remember the most relevant risk factors—ranging from trauma to splenectomy.
