see also:

• DVT prophylaxis
• DVT prophylaxis for the surgical patient
• DVT prophylaxis, anticoagulation and spinal anaesthesia or spinal cord injured patients
• Ix of suspected pulmonary embolism (PE)
• Mx of suspected DVT
• Mx of lower limb DVT
• Rx of venous thrombosis (DVT/PE) and superficial thrombophlebitis - American College of Chest Physicians guidelines 2012
• DVT and post-thrombotic syndrome (PTS)
• upper limb DVT
• thrombophlebitis
• thrombophilia
• thrombosis
• coagulation pathways
• anticoagulants
• varicose veins

• a deep venous thrombosis (DVT) is a significant thrombosis occurring within the deep veins of the lower limbs
• the main concern is the risk of potentially life threatening pulmonary embolism (PE) if a fragment or all of it breaks away and embolises into the pulmonary artery system
• it may also cause long term venous insufficiency in the affected limb
• it should be differentiated from a thrombophlebitis which is in the superficial veins and rarely embolise
• Virchow’s classic triad of causes of venous thrombosis - one or more of:
  • venous flow stasis (eg. lack of calf muscle pump - paralysis, anaesthesia, long haul flights; venous insufficiency, proximal obstruction such as external compression on a vein such as MTS)
  • endothelial wall injury (eg. IV catheters, inflammation, local compression, fractures, surgery)
  • hypercoagulability (eg. pregnancy, cancer, oestrogen, thrombophilia, etc)

• 0.1% (1in 1000) of adults develop a DVT each year
  • age under 40yrs: < 1 in 10,000 per year
  • age 30-49yrs: 2-3 per 10,000 per year
  • age 70-79yrs: ~20 per 10,000 per year (1 in 500)
• lifetime risk of DVT is ~2-5%

• these arise after a transient preceding event and hence the utility of this distinction is that such cases have reduced recurrence rates and thus can have shortened anticoagulation regimes
• examples include:
  • post-operative or hospitalisation (over 1/3rd of cases)
  • pregnancy / puerperium
    • during pregnancy: 22% occur in 1st TM (rate only marginally higher than non-pregnant patients), 34% in 2nd TM and 48% in 3rd TM
    • half of pregnancy-associated VTE events occur after delivery, especially the 1st 2 weeks, and risk remains elevated for roughly six weeks, sometimes up to 12 weeks¹⁾
    • 0.5–1.0 DVTs per 1,000 deliveries (including puerperal DVT)
    • more than half of pregnancy-related VTE are associated with thrombophilia; ²⁾
    • 0.5–1.0 DVTs per 1,000 deliveries (including puerperal DVT)
    • other major risks include caesarean delivery, postpartum infection, and the combination of obesity with immobilization. ³⁾
    • 0.5–1.0 DVTs per 1,000 deliveries (including puerperal DVT)
  • prolonged bed rest or immobilisation
  • immbolisation of the ankle eg. by plasters for Mx of fracture tibia or fibula, or Achille's tendon ruptures
  • prolonged air flights
• especially if compounded with dehydration or risk factors as below

• active cancer treatment (20% of cases)
• underlying undiagnosed cancer
• hormonal therapy especially oestrogens
• smoking
• hereditary thrombophilia
• pelvic pressure on pelvic veins eg. pelvic masses
• systemic lupus erythematosus (SLE) - especially in the 1st year after diagnosis
• May-Thurner syndrome (MTS):
  • the right iliac artery compresses the left iliac vein against the spine
  • this appears to be acquired rather than congenital
  • 20% to 25% of the general population (1st noted in 1957 and confirmed on later CT studies)⁴⁾ have the physical vein compression associated with May-Thurner syndrome, but it seems DVT only occurs in a minority
  • it may cause:
    • general increased risk of L leg DVT especially in women and this may explain the substantial left leg predominance of DVTs in women, or,
    • extensive unilateral iliofemoral DVT of left leg:
      • tend to have very high D-Dimer due to high clot burden eg. > 10 and often over 20
    • chronic venous insufficiency
    • iliac vein rupture
      • 28% of patients with iliac vein rupture have MTS
  • among patients who develop a DVT specifically in their left leg, the prevalence of underlying May-Thurner syndrome apparently jumps significantly, ranging from 18% to 49%⁵⁾
  • DVT usually occurs in women aged 20-50yrs (~72% of women are in this age range) and usually have another risk factor
  • risk is higher with scoliosis and prolonged sitting or standing
  • requires CT or MR venography to Dx hence it has historically been underdiagnosed and may be a cause of recurrent L DVTs as well as iliac vein rupture, chronic venous stasis and recurrent PEs
    • compression in excess of 70% as demonstrated at CT might be helpful for identifying possible underlying iliac vein compression syndrome (IVCS) in patients with a left lower extremity deep vein thrombosis.⁶⁾
  • Mx is of extensive thrombosis due to MTS is complex and may involve thrombolysis, radiologic or surgical Mx