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Not to be confused with aneurysm
In medicine, an embolism (plural embolisms; from the Greek ἐμβολισμός "insertion") is the event of lodging of an embolusinto a narrow capillary vessel of an arterial bed which causes a blockage (vascular occlusion) in a distant part of the body.
Embolization is a procedure that purposely creates such a lodging and occlusion of specific blood vessels with thrombo-emboli in order to deprive tumors (or other pathologic processes) of their perfusion (blood supply).
There are different types of embolism, some of which are listed below.
Arterial or venousEdit
Embolism can be classified as whether it enters the circulation in arteries or veins. Arterial embolism are those that follow and, if not dissolved on the way, lodge in a more distal part of the systemic circulation. Sometimes, multiple classifications apply; for instance a pulmonary embolism is classified as an arterial embolism as well, in the sense that the clot follows the pulmonary artery carrying deoxygenated blood away from the heart. However, pulmonary embolism is generally classified as a form of venous embolism, because the embolus forms in veins, e.g. deep vein thrombosis.
Main article: Arterial embolismArterial embolism can cause vessel occlusion in any part of the body. It is a major cause of infarction (which may also be caused by e.g. arterial compression, rupture or pathological vasoconstriction).
Emboli of cardiac origin are also frequently encountered in clinical practice. Thrombus formation within the atrium in valvular disease occurs mainly in patients with mitral valvedisease, and especially in those with mitral valve stenosis with atrial fibrillation (AF). In the absence of AF, pure mitral regurgitation has low incidence of thromboembolism. Absolute risk of emboli in idiopathic AF depends on other risk factors such as increasing age, hypertension, diabetes, recent heart failure, or previous stroke. Thrombus formation can also take place within the ventricles, and it occurs in approximately 30% of anterior-wall myocardial infarctions, compared with only 5% of inferior ones. Some other risk factors are poor ejection fraction (<35%), size of infarct, and the presence of AF. In the first three months after infarction, left-ventricle aneurysms have a 10% risk of embolization.
Patients with prosthetic valves also carry a significant increase in risk of thromboembolism. Risk varies, based on the valve type (bioprosthetic or mechanical); the position (mitral or aortic); and the presence of other factors such as AF, left-ventricular dysfunction, and previous emboli.
Further information: Pulmonary embolismAssuming a normal circulation, a thrombus or other embolus formed in a systemic vein will always impact in the lungs, after passing through the right side of the heart. This forms a pulmonary embolism that can be a complication of deep-vein thrombosis. Note that, contrary to popular belief, the most common site of origin of pulmonary emboli are the femoral veins, not the deep veins of the calf. Deep veins of the calf are the most common site of thrombi, not emboli origin.
Paradoxical (venous to arterial)Edit
In paradoxical embolism, also known as crossed embolism, an embolus from the veins crosses to the arterial blood system. This is generally found only with heart problems such as septal defects (holes in the cardiac septum) between the atria or ventricles. The most common such abnormality is patent foramen ovale, occurring in about 25 % of the adult population, but here the defect functions as a valve which is normally closed, because pressure is slightly higher in the left side of the heart. In certain circumstances, e.g. if patient is coughing just when an embolus is passing, passage to the arterial system may occur.
The direction of the embolus can be one of two types:
In anterograde embolism, the movement of emboli is in the direction of blood flow. In retrograde embolism, however, the emboli move in opposition to the blood flow direction; this is usually significant only in blood vessels with low pressure (veins) or with emboli of high weight.