Topic 11 - DVT

Question 1

What can trigger clot formation?

Answer 1

• venous stasis, vessel injury and hypercoagulability
Whatever the origin and initial biochemical path activated, the clotting process results in the activation of a common clotting pathway which converts prothrombin to thrombin by activation of factor Xa.

Question 2

What are some risk factors for DVT?

Answer 2

• Age
• Gender
• Pregnancy/Estrogen therapy Immobility/Obesity
• Heart disease
• Malignancy
• Trauma
• Sepsis
• Congenital Hypercoagulable states
• Previous DVT
• Varicose veins

Question 3

What is a hypercoagulable state?

Answer 3

• occur when substances promote platelet aggregation
• promote the activity of the coagulation cascade
• or when there is abnormal endothelial function.
• In general there are a number of genetic (Congenital) factors which promote the coagulation process and a number of non-genetic (Acquired) factors which promote hypercoagulability

Question 4

What are some congenital causes of hypercoagulation?

Answer 4

• Anti-thrombin iii deficiency
• Factor V resistance to protein C
• Protein C deficiency
• Protein S deficiency

Question 5

When may a hypercoagulation state be suspected?

Answer 5

• In some patients, there only appears to be one risk factor present at the time of developing DVT.
• In these cases, a second factor may be identified later in the patient’s treatment or after they have finished anticoagulation therapy.
• Many of the congenital clotting disorders are diagnosed after treatment has finished since the tests require cessation of anticoagulation therapy.

Question 6

What are some acquired hypercoagulable states?

Answer 6

• Malignancy
• Postoperative state
• Pregnancy
• Oral contraceptive
• Lupus anticoagulent
• Heparin induced thrombocytopaenia

Question 7

What is Virchows triad?

Answer 7

The formation of deep vein thrombosis (DVT) is dynamic and multifactorial.
Virchow’s triad describes three contributing factors for thrombus formation; venous stasis, vascular injury, and hypercoagulability.
Although there are many risk factors for DVT all can be related to one or more of the triad

Question 8

What are the most common areas for DVT formation?

Answer 8

• Clot does form more easily in calf veins, particularly the peroneal veins with the soleal veins and posterior tibial veins also frequently being the source of clot.
• The next most common segment to be involved is the popliteal vein, followed by the femoral vein, iliac veins and inferior vena cava.

Question 9

What is pulmonary embolism?

Answer 9

• occurs when a segment of venous clot is released from the site of thrombosis and carried to the heart where it is pumped via the pulmonary artery to lodge in the decreasing sized blood vessels of the lungs.

Question 10

What are the main symptoms of PE?

Answer 10

o	Dyspnea
o	Hemoptysis
o	Pleuritic Pain
o	Tachycardia
o	Atypical Asthma

Question 11

Why is ultrasound used when patients present with PE symptoms?

Answer 11

DVT may indirectly suggest the diagnosis of PE
• Because anticoagulation is most often the initial therapy for DVT and PE, it is reasoned that further investigation to exclude PE may not be necessary

Question 12

What are the limitations of using DVT to indirectly suggest PE?

Answer 12

o it does not make a definitive diagnosis of PE.
o Patients can have DVT and pulmonary symptoms and/or hemodynamic instability from causes other than PE.
o normal bilateral proximal venous ultrasound scans do not rule out PE.
o Even when PE is definitively present, DVT of the proximal lower extremity veins is detectable by compression ultrasound in only 50% of patients.

Question 13

What are the different modes for detect DVT?

Answer 13

o compression ultrasound (B-mode imaging only)
o duplex ultrasound (B-mode imaging and Doppler waveform analysis)
o color Doppler imaging alone.

Question 14

Which modes of ultrasound are used and when in DVT study?

Answer 14

• Compression ultrasound is typically performed on the proximal deep veins, specifically the common femoral, femoral, and popliteal veins,
• whereas a combination of duplex ultrasound and color Doppler imaging is more often used to interrogate the calf and iliac veins

Question 15

How accurate is proximal DVT study?

Answer 15

• sensitivity and specificity of venous ultrasonography are 97% and 94%,
• The high specificity of venous ultrasonography allows treatment of DVT to be initiated without further confirmatory tests
• the high sensitivity in diagnosing proximal DVT makes it possible to withhold treatment if the examination is negative

Question 16

When is there a need for serial DVT ultrasound examination?

Answer 16

• Due to limitations of some evaluations (oedema, obesity etc) there is a need for serial examinations or the performance of an alternative diagnostic procedure such as catheter-based contrast venography or CT (computed tomography) or MR (magnetic resonance) venography to exclude DVT.
• repeat or serial venous ultrasonography seems advisable for negative examinations in symptomatic patients who are highly suspicious for DVT and in whom an alternative form of imaging is contraindicated or not available.

Question 17

What are the ultrasound characteristics of DVT?

Answer 17

• Thrombus will obstruct the vein and prevent venous compression under transducer pressure
• colour Doppler filling defects in the veins indicating the presence of thrombus.
• Augmentation may suggest a clot between the transducer and the point of augmentation if there is reduced colour flow or a damped spectral waveform response.
• normal respiratory excursion and spontaneous flow of the CFV using Valsalva manoeuvre cannot exclude the presence of a proximal thrombus.
• loss of normal phasic flow suggests the presence of a proximal occlusion and should direct the sonographer to investigate the iliac veins and IVC

Question 18

Why is colour Doppler an excellent adjunct to bmode compression?

Answer 18

• When used in the longitudinal plane colour is not only able to identify the thrombus and characterise it as occlusive or non-occlusive but increases the accuracy of length quantification
• This approach is also useful as it can demonstrate thrombus that interval compression has missed or imaged poorly and has been shown to increase the accuracy of clot detection in the calf when combined with compression technique

Question 19

What are the different stages of clot resolution?

Answer 19

acute
sub acute
chronic

Question 20

Describe the ultrasound appearance of acute clot

Answer 20

• distended vein with hypoechic or anechoic luminal Bmode appearance.
• Colour usually shows no flow either spontaneously or with distal augmentation.
• A mobile or ‘free floating’ end to the thrombus may be visible in some cases

Question 21

Describe the ultrasound appearance of sub acute clot

Answer 21

• thrombus is more echogenic but may remain hypoechoic for some time.
• Free floating thrombus is no longer visible and patent channels appear, presumably from neovascularisation.
• The vein also becomes smaller and is often the same size as a non thrombosed vein.
• This is the most common stage to see patients who present in the outpatient setting

Question 22

Describe the ultrasound appearance of chronic clot

Answer 22

• Chronic thrombus develops in the months or years following an acute thrombosis.
• The vein may become small in diameter and the wall thickened with adherent clot incorporated into the wall tissue.
• The revascularisation and inflammation associated with clot resolution may cause permanent damage to the vein wall and venous valves, leaving the vein incompetent and the potential of post thrombotic disease developing.

Question 23

Where is superficial thrombophlebitis usually seen?

Answer 23

• may occur in any vein but is typically seen at sites of cannula insertion and in varicose veins in the leg.
• Multiple spontaneous thrombophlebitic episodes may also be related to an undected malignancy.

Question 24

What are the clinical indications of superficial thrombophlebitis?

Answer 24

o Pain and induration
o Erythema around the vein
o Tender and hardened cord along the course of the affected vein.

Question 25

A 54 yo man presents with marked leg swelling after recent arthroscopy. Explain why this man is at high risk for DVT

Answer 25

Virchow’s triad refers to the three main factors that may predispose somebody to having a DVT. These are:
• Trauma
• Stasis
• Hypercoaguability
Hypercoaguability is often related to a genetic predisposition or blood condition.
In this setting, the man has the first two factors which places him at risk.
(He may have the third but we don’t know this.)
He has had trauma in the form of knee surgery and the leg has consequently had a long period of immobility this causing venous stasis.

Question 26

1. Describe the differences in B-mode appearance between chronic and acute deep vein thrombus.

Answer 26

1. Chronic:
•	veins not distended or reduced diameter
•	thickened irregular walls
•	echogenic thrombus
•	coexistent deep venous insufficiency
•	collateral venous channels
•	lack of venous compression or partial compression
Acute:
•	sonolucent thrombus or internal echoes
•	change in vein calibre with respiration and Valsalva’s manoeuvre are lost
•	veins distended
•	lack of venous compression

Question 27

2. List the pitfalls associated with the Doppler ultrasound examination for patients suspected of having DVT

Answer 27

• Sonolucent acute thrombus.
• Reverberation may mimic thrombus in veins.
• Veins may collapse with usual transducer pressure.
• Duplicated venous system.
• Isolated thrombus in the adductor canal.
• Chronic thrombus may appear as isoechoic with the surrounding muscle.
Spectral Doppler waveforms may not vary with the Valsalva manoeuvre when the following are evident::
• partial thrombus with some venous flow;
• thrombus in calf veins; and/or
• well-developed collateral veins.

Question 28

List the examination modifications that enable you to achieve higher accuracy in the difficult to examine patient with suspected extremity DVT.

Answer 28

• Lower frequency transducer to increase penetration.
• Colour Doppler to confirm patency
• Valsalva to indirectly assess proximal patency.
• Change in patient position to decrease depth of veins.
• Further tilting of examination couch to increase vein distension.