Embolism

An embolism is the lodging of an, a blockage-causing piece of material, inside a. The embolus may be a blood clot, a globule , a bubble of  or other  , or. An embolism can cause partial or total blockage of in the affected vessel. Such a blockage (a ) may affect a part of the body distant from the origin of the embolus. An embolism in which the embolus is a piece of thrombus is called a thromboembolism.

An embolism is usually a pathological event, i.e., accompanying or. Sometimes it is created intentionally for a reason, such as to  or to kill a ous tumor by stopping its blood supply. Such therapy is called.

Classification
There are different types of embolism, some of which are listed below.

Embolism can be classified based on where it enters the circulation, either in or in. Arterial embolism are those that follow and, if not dissolved on the way, lodge in a more distal part of the. Sometimes, multiple classifications apply; for instance a is classified as an arterial embolism as well, in the sense that the clot follows the  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..

Arterial
can cause occlusion in any part of the body. It is a major cause of (tissue death from blockage of the blood supply).

An embolus lodging in the from either the  or a  will most likely be the cause of a  due to.

An arterial embolus might originate in the heart (from a thrombus in the, following or be a septic embolus resulting from ). Emboli of are frequently encountered in clinical practice. Thrombus formation within the atrium occurs mainly in patients with disease, and especially in those with   (narrowing), with  (AF). In the absence of AF, pure mitral regurgitation has a low incidence of thromboembolism.

The risk of emboli forming in AF depends on other risk factors such as age,, , recent , or previous. Thrombus formation can also take place within the, and it occurs in approximately 30% of anterior-wall s, 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 s have a 10% risk of emboli forming.

Patients with 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.

Emboli often have more serious consequences when they occur in the so-called "end circulation": areas of the body that have no redundant blood supply, such as the and.

Venous
Assuming a normal circulation, an embolus formed in a systemic will always impact in the lungs, after passing through the right side of the heart. This will form a that will result in a blockage of the  and can be a complication of. The most common sites of origin of pulmonary emboli are the. The deep veins of the calf are the most common sites of actual thrombi.

Paradoxical (venous to arterial)
In, 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, 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. Sometimes, for example if a patient coughs just when an embolus is passing, it might cross to the arterial system.

Direction
The direction of the embolus can be one of two types:
 * Anterograde
 * Retrograde

In anterograde embolism, the movement of emboli is in the direction of blood flow. In retrograde embolism, 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.

Etymology
The word embolism comes from the Greek ἐμβολισμός, meaning "interposition".