DVT – Why use Doppler?

Images Sarah Vaughan, text Genevieve Carbonatto

A young 26 year old girl presents to the Emergency Department with excrutiating pain to her left leg. She developed the pain acutely that morning and she can’t walk on it at all. She helps you with your diagnosis by saying that she has had a previous DVT in that leg and she is anxious she may have another one. She is not on anticoagulants.

On examination she cannot straighten her left leg because of  pain . She maintains her hip in flexion because it is the most comfortable position for her. Her left leg is slightly larger  than her right leg.

You get the ultrasound machine to check for a DVT. You start in the groin.  You are having lots of difficulty compressing the CFV because this causes her  pain. This is what you get

Note that you can’t compress the vein completely. Compression is very painful. There is a hyperechoic stripe in the vein that looks like a remant of her old DVT (synechiae). The lack of compression could be because of a partial thombus or because it is impossible to push hard enough.

To further investigate this area you decide to do a Doppler study on the vein.

Note the flat Doppler trace which exhibits no respiratory or cardac phasicity.

You check by getting the patient to do a Valsalva manoevre

The flow is interrupted with the Valsalva but there is no change in the trace after the Valsalva manoevre.There is no augmentation. The Doppler trace remains flat.

This is what a normal Doppler venous trace should look like.

Note the Doppler trace is not flat but shows respitatory variation or “phasicity”

This is what a normal Doppler trace with a Valsalva should look like.

Note that when there is no obstruction, the flow stops with breath holding during the Valsalva manoevre and then increases afterwards. This is called augmentation.

The flat trace in our patient’s Doppler  suggests that there may be  a more proximal venous thrombosis either in the common iliac vein or the IVC. A venogram is ordered . She has complete thrombosis of her left common iliac vein just before it enters the IVC. A CT scan confirmes she had May- Thurner syndrome. The combination of this as well as Factor V leiden heterozygosity and the oral contraceptive is found later to be the most likely cause for this thrombosis.

Venous Doppler

Normally , flow within the deep venous system is low resistance, the venous Doppler trace shows both respiratory phasicity and cardiac phasicity. Low intrathoracic pressures during inspiration causes increased flow to the heart. With the Valsalva manoevre flow ceases and is followed  by  augmented flow after the Valslava.

A flat venous Doppler trace  is an indirect sign of a deep vein thrombosis at a more proximal location. More precisely it is a sign of  proximal venous obstruction as venous flow may be interrupted intrisincally by thrombosis or extrinsically by tumour/abscess compression for example.  In both scenarios the Doppler trace will be flat. If there is flow in both common femoral veins (CFV) and  the Doppler trace is flat in both CFV’s then this suggests obtruction proximal to the CFV bifurcation such as in the IVC. If there is a flat trace in one CFV and a normal CFV Doppler waveform in the other then this suggests that the thrombosis is in the common iliac vein on the side of the flat trace, not in the IVC.  Respiratory factors can also cause loss of waveform phasicity. This loss of phasicity will be bilateral however and not asymetrical. (3)

Causes of iliofemoral DVT

There is usually at least one risk factor for venous thrombosis causing endothelial injury and hypercoagulability, along with stasis ( Virchow’s triad ) (2). These include

  • Postoperative state
  • Prolonged immobility (e.g., travel, hospitalization)
  • Malignancy
  • Inherited hypercoagulable conditions.
  • Pregnancy
  • May – Thurner syndrome anatomical variant in which the right common iliac artery overlies and compresses the left common iliac vein against the lumbar spine, found in 20 -24% of patients.

May – Thurner syndrome:

Iliofemoral DVT due to the right common iliac artery overlying and compressing the left common iliac vein against the lumbar spine.

  • First described in 1957. 22% of 430 cadavers on autopsy were found to have this  anatomical variant. 22 – 24% of patients showed this variant using CT scans. Despite the relatively high incidence of this anatomical variation, the clinical prevalence of MTS-related DVT is low,  occurring in only 2% to 3% of all lower extremity DVTs (4)
  • It is probably underdiagnosed as a cause of DVT because patients with this problem also have another recognised risk factor for DVT such as being on the oral contraceptive, being pregnant or having a coagulopathy. Investigations are not pursued to look for  it so is rarely diagnosed.
  • Systemic anticoagulation alone is rarely effective and mechanical thrombectomy and stent placement is often necessary if the DVT is in the iliofemoral veins. Catheter directed thrombolysis for  extensive iliofemoral DVT is the new treatment achieving faster and more complete thrombolysis and reducing post thrombotic syndrome.
  • Because the thrombus occurs high in the pelvis it can be missed as a potential diagnosis in the ED. Clearly simple venous compression at the level of CFV will not diagnose a more proximal obstruction but a Doppler study in this situation is useful . If a proximal thrombus is suspected then further investigation with contrast venogram or MRI is indicated .

A special mention should be made of DVT in  pregnancy as an iliofemoral DVT  can be overlooked in the Emergency Department. Any pregnant woman presenting with a possible diagnosis of  DVT should have an  investigation for an  iliofemoral DVT. The incidence of DVT’s overall is  5 x higher in pregnancy than in age matched controls in non pregnant patients and most frequently found  either in the calf veins or in the iliofemoral segment of the deep venous system.

Predisposing factors  for DVT in pregnancy include:

  • Hypercoagulability, stasis and endothelial injury during pregnancy and puerperium.
  • Increased levels of clotting factors together with decreased fibrinolysis and reduced levels of protein S.
  • Pressure on the IVC by the gravid uterus.
  • Decreased flow velocity and increased vessel diameter of the deep leg veins . At term, flow velocity of the femoral vein slows to less than 1/3 of the velocity recorded in the 1st trimester and subsequently in the post partum period.

Teaching point: Vein compression remains  the examination of choice when assessing for a DVT. Doppler however is useful in identifying the presence of proximal venous obstruction . A  flat Doppler trace with loss of respiratory phasicity  is an indirect sign of a more proximal occlusive DVT or a more proximal venous obstruction from a tumour, a node or an abscess for example.

References

  1. Turk J Emergency Med 2015 Sep; 15(3): 147–149. Rare etiological causes of iliofemoral deep venous thrombosis: Reports of 2 cases Emrah Ereren,a Ali Kemal Erenler,b,∗ Vedat Bakuy,a Mustafa Omer Yazicioglu,c and Sercan Dumana
  2. Amer College of Cardiol  Iliofemoral Deep Vein Thrombosis Nov 24, 2015 | T. Raymond Foley, MD; Stephen W. Waldo, MD, FACC; Ehrin J. Armstrong, MD, FACC Expert Analysis
  3. AJR Am J Roentgenol 997 Dec;169(6):1721-5. Normal lower limb venous Doppler flow phasicity: is it cardiac or respiratory? Abu-Yousef MM1, Mufid M, Woods KT, Brown BP, Barloon TJ.
  4.  Proc (Univ Med Cent) 2012 Jul; 25(3): 231–233. May-Thurner syndrome: a not so uncommon cause of a common condition
  5. Expert Rev Cardiovasc Ther: 2016;14(2):189-200 catheter-directed thrombolysis for extensive iliofemoral deep vein thrombosis:review of literature and ongoing trials Liew A,Douketis J

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