Thrombosis natural history, complications and prognosis
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Thrombosis Microchapters |
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Site of Thrombosis |
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Differentiating Thrombosis from other Diseases |
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Diagnosis |
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Treatment |
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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]
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Complications
A stable thrombus when dislodged from its place is called an embolus (pleural emboli). Without an infection, the thrombus may become detached and enter circulation as an embolus, finally lodging in and completely obstructing a blood vessel (an infarction). The effects of an infarction depend on where it occurs.
Most thrombi, however, become organized into fibrous tissue, and the thrombosed vessel is gradually recanalized. If a bacterial infection is present at the site of thrombosis, the thrombus may break down, spreading particles of infected material (septic embolus) throughout the circulatory system and setting up metastatic abscesses wherever they come to rest. This might cause pyemia.
The major outcomes of thrombosis are death, recurrence, post-thrombotic syndrome and major bleeding due to anticoagulation. Thrombosis is also associated with impaired quality of life, particularly when post-thrombotic syndrome develops. Death occurs within one month of an episode in about 6% of those with deep venous thrombosis and 10% of those with pulmonary embolism.
Prognosis
Thrombus formation can have one of five outcomes: propagation, embolization, dissolution, organization and organization with recanalization.
- Propagation of a thrombus occurs towards the direction of the heart. This means that it is anterograde in veins or retrograde in arteries.
- Embolization occurs when the thrombus breaks free from the vascular wall and becomes mobile. A venous emboli (most likely from deep venous thrombosis in the lower extremities) will travel through the systemic circulation, reach the right side of the heart, and travel through the pulmonary artery resulting in a pulmonary embolism. On the other hand, arterial thrombosis resulting from hypertension or atherosclerosis can become mobile and the resulting emboli can occlude any artery or arteriole downstream of the thrombus formation. This means that cerebral stroke, myocardial infarction, or any other organ can be affected.
- Dissolution occurs when fibrinolytic mechanisms break up the thrombus and blood flow is restored to the vessel. This may be aided by drugs (for example after occlusion of a coronary artery). The best response to fibrinolytic drugs is within a couple of hours, before the fibrin meshwork of the thrombus has been fully developed.
- Organization and recanalization involves the ingrowth of smooth muscle cells, fibroblasts and endothelium into the fibrin-rich thrombus. If recanalization proceeds it provides capillary-sized channels through the thrombus for continuity of blood flow through the entire thrombus but may not restore sufficient blood flow for the metabolic needs of the downstream tissue.