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PH-CV07

Deep vein thrombosis

How the calf muscle pump and venous valves return blood from the legs, why stasis, vessel injury and a clotting tendency combine to form a clot in a deep vein, and how that clot causes a swollen leg and can travel to the lungs.

By the end, you can

  • Describe the deep veins of the leg and how the calf muscle pump and valves return blood.
  • Explain Virchow’s triad and relate common risk factors to each component.
  • Explain how a thrombus forms in a valve pocket and grows along the vein.
  • Relate leg swelling, pain and warmth to venous obstruction and inflammation.
  • Explain pulmonary embolism and the post-thrombotic syndrome as consequences.
  • Recognise the classic appearances, scores and tests of DVT, and explain how anticoagulants and other treatments act on its mechanism.

What it is

Deep vein thrombosis (DVT) is a blood clot (thrombus) in a deep vein, most often in the calf or thigh. With pulmonary embolism it makes up venous thromboembolism (VTE). Clots in the calf veins alone are called distal; those reaching the popliteal vein or above are proximal and more likely to embolise.

2 types to tell apart
Distal (calf) DVT
Confined to the calf veins; many dissolve, but some extend upwards.
Proximal DVT
Involves the popliteal, femoral or iliac veins; larger and more likely to cause pulmonary embolism.

Normal function

Pumping blood up the leg

Blood from the calf drains into deep veins running with the arteries: the , and . They join behind the knee as the , which continues up the thigh as the . Superficial veins such as the drain into them.

Standing, blood must rise a metre or more against gravity. Each step contracts the calf muscles, such as , which squeeze the deep veins and drive blood upwards: the calf muscle pump. One-way valves stop it falling back.

Blood normally stays liquid because endothelium releases anticoagulant signals and because flow keeps clotting factors moving. Small clots that do form are dissolved by the fibrinolytic system.

Point to it on the model