Deep vein thrombosis

Pathophysiology

• Thrombosis is a protective mechanism to prevent blood loss and seal off damaged blood vessels
• Caused by an imbalance between the homeostatic factors normally involved in blood flow and thrombosis
• Commonest in the lower limb, especially at low-flow sites such as soleal sinuses
• Virchow's Triad
  • Damage to the vessel wall
  • Blood flow turbulence
  • Hypercoagulability

Classification:

• Proximal DVT is defined by the Austin guideline as anything proximal to popliteal vein
  • 25% risk of PE if untreated
• Distal DVT, distal to popliteal vein
  • Limited sensitivity of DUS - repeat it in one week if clinical picture suggestive but USS negative
  • 1% risk of PE if untreated
• Superficial VTE
  • Most commonly GSV, SSV and tributaries of those
  • Concomitant DVT and PE observed in 25% and 5% of patients respectively
  • VV in 80-90% of patients

Risk factors

• Intrinsic
  • Genetic
    • Family history thrombophilia
    • Factor V Leiden
    • Prothrombin G20210A mutation
    • Protein C, S or antithrombin deficiency
    • Sickle cell trait
    • APLS
    • May-Thurner syndrome
      • Compression of left CIV by overlying right CIA
      • Consider this in patients with unprovoked left iliofemoral vein occlusion and investigate with CT
• Secondary
• Specific for upper limb DVT:
  • Venous catheter use (CVC)
    • Especially with underlying malignancy
    • CVC 1-3%, PICC 2-4%
    • Superficial venous (cephalic or basilic) - intermediate dose LMWH until 2 weeks post line removal
    • Extensive or DVT - full dose LMWH or DOAC until 3 months post removal
    • Can leave catheter in until no longer required, if functioning
  • Underlying malignancy
  • Younger age
  • Athletic muscular male
  • Strenuous upper limb extremity activity or repetitive arm hyperabduction
  • Anatomic abnormalities of the thoracic outlet (e.g. congenital abnormalities of cervical rib, supernumerary muscles, abnormal tendon insertions) causing axillosubclavian compression
    • All patients should have a CXR with cervical rib views or dynamic USS/CT
  • IV drug use

Risk stratification

• Rogers/Caprini scores

Natural history

• Recanalisation
  • Occurs in most patients over time
  • Begins early, generally within 3 months
  • Complete thrombus resolution in 56% of patients at 9 months
• Recurrence
  • 30% will get a recurrence within 10 years
  • Independent risk factors for recurrence - old age, obesity, malignancy, extremity paresis

Approach to the patient with significant DVT when considering thrombus removal

• Identify cause
  • Thrombophilia evaluation (see 'thrombosis' under 'periop medicine')
  • Malignancy screening - CT chest/abdo/pelvis and other testing as per 'thrombosis' section under 'periop medicine'
• Define full proximal and distal extent of the thrombus, preferably including IVC
  • Imaging
    • CT chest/abdo/pelvis is useful - 50% will have a PE, which will be useful to know about although not necessarily changing anticoagulation guidelines (what if they start getting chest pain next week?)
    • Any patient with unexplained tachycardia, tachypnoea, desaturation, hypotension or symptoms of dyspnoea or chest pain should be investigated for PE
• Prevent PE
  • Anticoagulation
  • IVC filters - in the setting of absolute contraindication to therapeutic anticoagulation
• Consider thrombus removal in those patients at risk for PTS
• Anticoagulate

Treatment:

• Superficial venous thrombosis
  • Treat with anti-inflammatories and LMWH for 45 days
  • Needs USS too to exclude DVT
• DVT
  • Medical (for choice of anticoagulant, look under 'periop medicine' -> 'thrombosis'
    • Upper limb DVT
      • Therapeutic anticoagulation for at least 3 months
      • USS as baseline prior to ceasing
    • Proximal DVT:
      • Recommendations as per Austin Thrombosis guideline
      • First unprovoked proximal DVT - minimum 3 months, but consider longer
      • Second unprovoked DVT - long term
      • First provoked proximal DVT - Minimum 3 months
      • Second or recurrent provoked DVT - minimum 3 months
      • High-risk features consider >6 months or lifetime
      • Those with occlusion of CFV should be admitted and considered for thrombus removal
      • Beware of females of childbearing potential - avoid pregnancy while on warfarin or DOAC
      • Repeat DUS should be performed prior to cessation of anticoagulation, as a baseline
    • Distal DVT:
      • Asymptomatic - may not require anticoagulation. Follow-up DUS in 2/52 and only treat if there is proximal extension.
      • Symptomatic:
    • SVT:
  • Surgical
    • The rationale for treatment is to prevent PTS - see below for pathophysiology
    • Decide whether to operate or not, then pick the most appropriate modality (see flowchart below)
    • Rutherford's actually advocates pursuing thrombus removal for all patients with IFDVT who are at risk of PTS. Also consider thrombus removal for those with thrombotic obliteration of popliteal and proximal tibial veins, as they can get bad below-knee PTS.
    • Removal of thrombus is difficult after two weeks
    • Patients with limb-threatening venous ischaemia due to IFDVT causing venous outflow obstruction should have thrombus removal if possible
    • Indications
      • Lower limb - consider in younger patients with iliofemoral DVT, avoid in patients >60 generally
      • Upper limb - venous gangrene or venous TOS which you are going to fix
    • Modalities:
      • Thrombolytic therapy
        • Catheter-directed thrombolysis
          • Safer and more effective than systemic infusion, and also prevents wasting the drug
          • Mechanism - activation of fibrin-bound plasminogen and resultant production or plasmin
          • Success rates of 75-90% are achieved, and most have good DVT-free long-term survival
          • Bleeding complications 5-11% (mostly the access site)
          • Serious distant bleeding is uncommon and intracranial bleeding rare
        • Pharmacomechanical thrombolysis
          • Endovascular mechanical thrombectomy
            • Amplatz, Angiohet, Trerotola, Oasis products
            • Combination of mechanical device and plasminogen activator removed 82% of thrombus
            • Faster than CDT alone
          • USS-accelerated Thrombolysis
          • Endovascular Aspiration Thrombectomy
      • Operative Venous Thrombectomy
        • Effective short and long-term outcomes, few complications
        • Superior to anticoagulation alone for ileofemoral DVT in terms of patency, venous pressure, leg oedema and PTS
        • Roughly similar results to catheter-directed thrombolysis for IFDVT
        • Benefits are the ability to achieve proximal patency and maintain distal valve competence
        • Need to be sure to remove all thrombus, correct underlying lesions and maintain therapeutic anticoagulation post-operatively

From Rutherford's:

Complications:

• Post-thrombotic syndrome
  • Defined as the signs and symptoms resulting from acute DVT
  • Pathophysiology
    • Ambulatory venous hypertension resulting from valve reflux and/or luminal obstruction (most severe when both are present)
    • Leads to swelling, pigmentation, and lipodermatosclerosis
  • Risk factors:
    • Iliofemoral DVT, especially when treated with anticoagulation alone. 40% demonstrate venous claudication and 15% develop venous ulceration within 5 years.
    • Ipsilateral recurrent DVT, which occurs more commonly in patients with a large thrombus burden
  • Diagnosis
    • Venous haemodynamics are adversely affected long before it can be detected by imaging
  • Treatment
    • Principles
      • Prevented by early elimination of thrombus
      • Luminal obstruction seems to be especially important, which is why treatment is aimed at removing it
      • Removal of thrombus can also preserve valvular function
      • Prevention of PTS improves QoL and prevents recurrence