topic 10 DVT

Question 1

Describe the process of clot formation.

Answer 1

• Circulating platelets are primarily involved with initiating the clotting process
• Normal epithelium produces substances that prevent platelets from activating and initiating the clotting process
• platelets normally adhere weakly to the vessel wall but in cases of inflammation or trauma to the vein wall, the platelets will adhere more strongly forming a platelet plug
• physical trauma enhances platelet adhesion
• once there is sufficient activation, the platelets release chemicals which trigger a series of enzyme-driven reactions called the coagulation cascade to convert inactive prothrombin into active thrombin
• thrombin converts fibrinogen into fibrin which is formed as a layered mesh-work around the platelets
• The mesh of platelets and fibrin form the blood clot, which entraps RBC and more platelets

Question 2

What is Virchow’s triad?

Answer 2

• venous stasis
• vessel injury
• hypercoagulability

The presence of any 2 of these factors will increase the risk of forming a DVT.

Question 3

List some congenital factors associated with DVT

Answer 3

• Anti-thrombin III deficiency
• Factor V resistance to protein C
• Protein C deficiency
• Protein S deficiency
• Homocystinuria
• Dysfibrinogenemia

Fibrinolytic disorders can cause thrombosis where the normal degrading mechanism may be impaired and promote hypercoagulability

Question 4

List some acquired factors that increase blood’s coagulability

Answer 4

• malignancy
• post-operative state
• pregnancy
• oral contraceptive
• lupus anticoagulant
• heparin-induced thrombocytopaenia

Question 5

Where does clot form more easily?

Answer 5

In the calf veins, particularly in the peroneals

Question 6

How do DVT act when untreated?

Answer 6

Untreated, isolated calf clot has a 20-25% risk of propagating to more proximal veins. They resolve in about 65% of patients within 6 months. Clots in proximal veins take considerably longer to resolve.

Question 7

Describe the resolution of a clot

Answer 7

Clot resolves at different rates depending on the extent of the clot and which veins are involved. Clot in calf veins are usually quicker to improve or result than clot in the upper thigh or abdomen. As clot resolves, residual clot becomes adhered to the walls and are less likely to break loose and cause a pulmonary embolus

Question 8

what is superficial thrombophlebitis?

Answer 8

Superficial thrombophlebitis is thrombus within the superficial venous system. Patients may present with pain and induration, erythema around the vein and a tender and hardened cord along the course of the affected vein. In 12-23% of patients, there may be extension into the deep system through perforators, the SFJ and the SPJ.

Question 9

Describe the sonographic appearance of an acute DVT

Answer 9

The vein will be distended with hypoechoic or anechoic luminal clot in b-mode. Colour usually shows no flow spontaneously or with distal augmentation. A free-floating end of thrombus may be visible

Question 10

Describe the sonographic appearance of sub-acute thrombus

Answer 10

The thrombus will be more echogenic but may still remain hypoechoic. The free-floating thrombus is no longer visible. Patent channels may appear. The vein becomes small again. this is the most common time to see people in the outpatient setting.

Question 11

Describe the sonographic appearance of chronic thrombus

Answer 11

This thrombus develops in the months or years following an acute thrombus. The vein may become small in diameter. There may be wall thickening. Adhered clot is incorporated into the wall tissue. Revascularisation and inflammation associated with clot resolution may cause permanent damage to the vein wall and venous valves,. There is the potential of post-thrombotic disease developing.