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Questions and Answers
What is the direction of growth of arterial thrombi from the point of attachment?
What type of thrombi forms in the sluggish venous circulation and contains more enmeshed erythrocytes?
What is the primary influencer of thrombus formation in the heart or arterial circulation?
Which of the following is a secondary disorder of hypercoagulability?
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What is the primary mechanism of venous thrombosis?
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What is the most significant clinical consequence of venous thrombi?
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What is the role of plasmin in fibrinolysis?
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What is the term for thrombi that form in heart chambers or in the aortic lumen?
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What is the primary mechanism by which turbulence contributes to thrombus formation?
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Where can thrombi develop in the cardiovascular system?
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What is the characteristic of arterial thrombi?
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What is the fate of a thrombus that breaks loose from the vascular surface?
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What is the role of t-PA in fibrinolysis?
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What is the characteristic of thrombi that have grossly and microscopically apparent laminations?
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What is the definition of hypercoagulability?
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What is Virchow's triad?
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What is the most common location of venous thrombi?
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Which of the following is a major initiator of thromboses?
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What is the term for a detached intravascular solid, liquid, or gaseous mass that is carried by the blood to a site distant from its point of origin?
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What is the most common consequence of thromboembolism?
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Which of the following types of thrombi rarely embolize?
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What is the incidence of pulmonary embolism in hospitalized patients?
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What is the cause of atrial mural thrombi in rheumatic heart disease?
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What is the approximate number of deaths per year in the United States due to pulmonary embolism?
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Study Notes
Venous Thrombosis (Phlebothrombosis)
- Most venous thrombi occur in the superficial or deep veins of the leg.
- Superficial venous thrombi usually occur in the saphenous system, particularly when there are varicosities.
- Superficial thrombi can cause local congestion, swelling, pain, and tenderness along the course of the involved vein.
- Deep thrombi in the larger leg veins at or above the knee joint are more serious because they may embolize.
- Deep venous thrombosis can occur with stasis or in a variety of hypercoagulable states.
Cardiac and Arterial Thrombosis
- Atherosclerosis is a major initiator of thromboses, because it is associated with loss of endothelial integrity and abnormal vascular flow.
- Cardiac mural thrombi can occur in the setting of myocardial infarction related to dyskinetic myocardial contraction and damage to the adjacent endocardium.
- Rheumatic heart disease can cause atrial mural thrombi due to mitral valve stenosis, followed by left atrial dilation and concurrent atrial fibrillation.
Embolism
- An embolus is a detached intravascular solid, liquid, or gaseous mass that is carried by the blood to a site distant from its point of origin.
- Virtually 99% of all emboli represent some part of a dislodged thrombus, hence the term thromboembolism.
- Rare forms of emboli include fat droplets, bubbles of air or nitrogen, atherosclerotic debris, tumor fragments, bits of bone marrow, or foreign bodies such as bullets.
- The consequences of thromboembolism include ischemic necrosis (infarction) of downstream tissue.
Pulmonary Thromboembolism
- Pulmonary embolism has an incidence of 20 to 25 per 100,000 hospitalized patients.
- Although the rate of fatal pulmonary emboli has declined from 6% to 2% over the last quarter century, pulmonary embolism still causes about 200,000 deaths per year in the United States.
Thrombosis Pathogenesis
- There are three primary influences on thrombus formation (called Virchow's triad): endothelial injury, stasis or turbulence of blood flow, and blood hypercoagulability.
- Endothelial injury is particularly important for thrombus formation occurring in the heart or in the arterial circulation.
- Alterations in normal blood flow, such as turbulence, contribute to arterial and cardiac thrombosis.
- Hypercoagulability is loosely defined as any alteration of the coagulation pathways that predisposes to thrombosis, and it can be divided into primary (genetic) and secondary (acquired) disorders.
Morphology
- Thrombi can develop anywhere in the cardiovascular system (e.g., in cardiac chambers, on valves, or in arteries, veins, or capillaries).
- The size and shape of a thrombus depend on the site of origin and the cause.
- Thrombi are focally attached to the underlying vascular surface; arterial thrombi tend to grow in a retrograde direction from the point of attachment, while venous thrombi extend in the direction of blood flow.
- Thrombi can have grossly (and microscopically) apparent laminations called lines of Zahn.
Fate of the Thrombus
- Thrombus can undergo propagation, embolization, dissolution, organization, and recanalization.
Clinical Correlations: Venous versus Arterial Thrombosis
- Thrombi are significant because they cause obstruction of arteries and veins and are potential sources of emboli.
- Venous thrombi can cause congestion and edema in vascular beds distal to an obstruction, but they are most worrisome for their capacity to embolize to the lungs and cause death.
- Arterial thrombi can embolize and even cause downstream tissue infarction, but their role in vascular obstruction at critical sites (e.g., coronary and cerebral vessels) is much more significant clinically.
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Description
This quiz covers the causes and effects of venous thrombosis, including superficial and deep thrombi in the leg veins, and their symptoms.
