Prof Gerry O’ Sullivan, Consultant Interventional Radiologist, National University Hospital, Galway, Ireland
Thrombosis is the formation of a blood clot, called a thrombus, in a blood vessel. The two broad classifications of thrombosis are venous and arterial, depending on whether the clot develops in the vein or an artery. Venous and arterial thrombosis are variations of similar pathologic mechanisms but there are differences in their morphology.
Arterial thrombosis occurs under high shear flow when platelet rich thrombi are formed around ruptured atherosclerotic plaques and damaged endothelium. Venous thrombosis occurs under low shear flow and mostly around intact endothelial wall. Venous thrombi are fibrin rich, encapsulating a large amount of red blood cells in addition to activated platelets.
Venous thromboembolism or VTE is a condition in which blood clots form most often in the deep veins of the leg, known as deep vein thrombosis or DVT, and can travel in the circulation and lodge in the lungs, known as pulmonary embolism or PE.
Together, DVT and PE make up VTE, which is the third most common cause of death after heart attack and stroke. Every year, there are approximately 10 million cases of VTE worldwide. In the U.S., there are approx. 250, 000 VTE-related deaths every year, while in Europe, there are approx. 544,000 VTE-related deaths every year. Up to 60 % of VTE cases occur during or after hospitalisation, making it a leading preventable cause of hospital death.
DVT can be associated with acute complications such as PE and longer-term complications such as post-thrombotic syndrome (PTS). PTS refers to symptoms and signs of chronic venous insufficiency that can develop following DVT and is a burdensome and costly complication. A combination of reflux due to valvular incompetence and venous hypertension due to thrombotic obstruction is thought to underlie the pathophysiology of PTS. Symptoms and signs of PTS may include leg pain, leg heaviness, vein dilation, edema, skin pigmentation and venous ulcers.
In addition to the disease burden, VTE can cause significant global economic burden. In the U.K., VTE costs the National Health Service £640 million per year, and in the U.S., diagnosis and treatment of VTE costs $15.5 billion per year.
The treatment of venous disease is gaining increasing importance among Interventional Physicians. While the arterial endovascular management of peripheral arterial disease has progressed rapidly in the past 2 decades, venous disease is at a relatively early stage of innovation.
Traditionally, primary treatment for DVT has focused on anticoagulation, rather than thrombus removal. Anticoagulation therapy does not remove existing thrombus but rather prevents the propagation of the thrombus.
Endovascular clot removal methods can provide immediate symptom relief and, by removing clot early, physicians can identify an underlying obstructive lesion that may require a stent. Current endovascular treatment methods involve catheter-directed thrombolysis (CDT), percutaneous mechanical thrombectomy (PMT), balloon venoplasty, iliac vein stenting, and manual aspiration.
Mechanical thrombectomy devices can be used when there is a contra-indication to fibrinolysis and/or anticoagulation or can be used in conjunction with lytic agents if no such contraindication exists.
The rationale to remove thrombus from the deep veins of patients with acute DVT is to restore patency, preserve valvular function and thereby avoid post-thrombotic morbidity. It has been repetitively shown in multiple trials that thrombolysis and/or thrombectomy improves the rate of patency of the iliofemoral venous segment.