Deep vein thrombosis Flashcards
What is deep vein thrombosis (DVT)?
DVT is the development of a blood clot in a major deep vein in the leg, thigh, pelvis or abdomen which may result in impaired venous blood flow and consequent leg swelling and pain.
Aetiology of DVT
Slight perturbations in the coagulation system can lead to bleeding or thrombosis.
3 factors individually or together, lead to most DVTs are vessel injury, venous stasis and activation of the clotting system (Virchow’s triad).
-Thus many patients who develop DVT have a trigger that leads to blood coagulation (surgery or trauma), prolonged immobility that leads to stasis, or medications or illnesses (cancers, antiphospholipid syndrome) that can stimulate clotting.
How does thromboembolic risk factors affect the diagnosis of DVT?
The presence or absence of thromboembolic risk factors relative to the diagnosis of DVT have a major impact on determining the length of time that anticoagulant therapy is offered.
Classification of DVT
There’s a 4 category system:
- Major transient provocation (surgery lasting >60 minutes) occurring within 3 months prior to thrombosis.
- Minor transient provocation (oral contraceptives, medical hospitalisation) occurring within 2 months.
- Unprovoked
- Persistent provocation (e.g. active cancer)
Pathophysiology of DVT
- Most blood clots that develop in the deep veins of the leg begin to form above and behind a venous valve.
- Clots often resolve spontaneously.
- A clot might occlude the entire lumen, many DVTs arise in the calf veins and propagate proximally.
- The body’s fibrinolytic systems begin to dissolve a clot as it forms and breakdown products like D-dimer appear in the blood.
Signs and symptoms of DVT
- Unilateral leg and thigh swelling.
- Oedema and dilated collateral superficial veins on the affected side.
- Tenderness along the path of the deep veins.
- Tenderness with dorsiflexion of the foot (Homans’ sign) and calf pain on palpation (Pratt’s sign) may be present. They, however, have poor sensitivity and specificity.
- When massive, the swelling can obstruct deep and superficial venous outflow as well as arterial inflow.
D-dimer as a test for DVT
D dimer test is a useful test to exclude the presence of an acute DVT.
D dimer is non-specific and is often positive in older patients, acutely ill, hepatic disease, infection or are pregnant.
Positive D-dimer test with low Well’s score prompt clinician to proceed with imaging.
Investigations of DVT
Wells score D-dimer level Proximal duplex ultrasound Whole-leg ultrasound INR and aPTT Urea and creatinine LFTs FBC
What is a venous duplex ultrasound?
This is the first-line test in all patients with Well’s score >2
It assesses for the presence of thrombus by compressibility and venous flow by the use of Doppler.
Diagnosis of an acute clot is based on the inability to completely collapse the walls of the vein in the transverse plane by pressing down on the vein with a transducer probe.
Two techniques: whole leg ultrasound and proximal DUS
Differentials of DVT
Cellulitis Calf muscle tear Calf muscle haematoma Ruptured baker's cyst Pelvic/thigh mass compressing venous outflow from the leg.
Management of VTE
Anticoagulation is the mainstay of therapy for the treatment of DVT. The reasons patients are treated with anticoagulants are to:
Prevent propagation/progression of the thrombus in the deep veins in the legs
Reduce the risk of pulmonary embolism (PE)
Reduce the risk of recurrent DVT.
Anticoagulant therapy for DVT has been described in three phases: initiation, long-term, and extended.
-Initiation (5-21 days following diagnosis): goals of care are to arrest the active prothrombotic state and to inhibit thrombus propagation and embolisation.
-Long-term (initiation to 3 months): goals are to prevent new thrombus while the original clot is stabilised and intrinsic thrombolysis is underway.
-Extended (3 months to indefinite): the goal is secondary prevention of new venous thromboembolism (VTE).
Treatment of VTE
- DOACs is recommended over vitamin K antagonist (warfarin) which is in turn recommended over LMWH.
- LMWH is preferred in active cancer, obesity, pregnancy and hepatic impairment.
- Fondaparinux is reserved for patients with HIT or those with a history of this condition.
- UFH followed by warfarin is used in renal impairment.
- Catheter-directed thrombolysis with mechanical removed used in selected patients with iliofemoral acute DVT who are at low risk for bleeding.
Complications of DVT
Heparin-induced thrombocytopenia (HIT) PE Bleeding during initial treatment Heparin resistance Osteoporosis due to heparin treatment
