Embolism

An embolism is the sudden blockage of a blood vessel by a blood clot that has been brought to that location by the bloodstream. The clot, called an embolus, from the Greek word meaning plug, is a blood clot that has formed inside the circulatory system and is floating in the bloodstream. It will remain on the move until it encounters a blood vessel too small for it to fit through, where it will plug the vessel and prevent any further circulation of blood through it. The plural of embolism is emboli.

A blood clot that forms in a given location and remains there is called a thrombus, from the Greek word for clot.

An embolism is named by the location in which the clot lodges. A pulmonary embolism is an embolus that has plugged a blood vessel, usually an artery, in one of the lungs. A coronary embolism is obscuring the channel in one of the coronary arteries, which feed the heart muscle. A cerebral embolism lodges in a blood vessel in the brain and perhaps precipitates a stroke.

Of the three general categories of emboli—coronary (arterial), cerebral (gas), and pulmonary—pulmonary emboli are the most common.

In coronary (arterial) emboli, blood flow is blocked at the junction of major arteries, most often at the groin, knee, or thigh. Arterial emboli are generally a complication of heart disease. An arterial embolism in the brain (cerebral embolism) causes stroke, which can be fatal. An estimated 5 to 14% of all strokes are caused by cerebral emboli. Arterial emboli to the extremities can lead to tissue death and amputation of the affected limb if not treated effectively within hours. Intestines and kidneys can also suffer damage from emboli.

Cerebral (gas) emboli result from the compression of respiratory gases into the blood and other tissues due to rapid changes in environmental pressure, for example, while flying or scuba diving. As external pressure decreases, gases (like nitrogen) which are dissolved in the blood and other tissues become small bubbles that can block blood flow and cause organ damage.

In a pulmonary embolism, a common illness, blood flow is blocked at a pulmonary artery. When emboli block the main pulmonary artery and in cases where there are no initial symptoms, a pulmonary embolism can quickly become fatal. According to the American Heart Association, an estimated 600, 000 people in the United States develop pulmonary emboli annually and 60, 000 people die from it each year.

Common symptoms of a pulmonary embolism include:

• Labored breathing, sometimes accompanied by chest pain,
• A rapid pulse,
• A cough that may produce sputum,
• A low-grade fever, and
• Fluid build-up in the lungs.

Less common symptoms include:

• Coughing up blood,
• Pain caused by movement or breathing,
• Leg swelling,
• Bluish skin,
• Fainting, and
• Swollen neck veins.

Symptoms of an coronary embolism include:

• Severe pain in the area of the embolism,
• Pale, bluish cool skin,
• Numbness,
• Tingling, and
• Muscular weakness or paralysis.

Risk factors for coronary and pulmonary emboli include: prolonged bed rest, surgery, childbirth, heart attack, stroke, congestive heart failure, cancer, obesity, a broken hip or leg, oral contraceptives, sickle cell anemia, chest trauma, certain congenital heart defects, and old age. Risk factors for cerebral emboli include: scuba diving, amateur airplane flight, exercise, injury, obesity, dehydration, excessive alcohol, colds, and medications such as narcotics and antihistamines.

A pulmonary embolism is difficult to diagnose, with less than 10% of patients who die from a pulmonary embolism being diagnosed with the condition. More than 90% of cases of pulmonary emboli are complications of deep vein thrombosis, blood clots in the deep vein of the leg or pelvis.

Arterial emboli are usually a complication of heart disease where blood clots form in the heart’s chambers. Gas emboli are caused by rapid changes in environmental pressure that could happen when flying or scuba diving. A pulmonary embolism is caused by blood clots that travel through the blood stream to the lungs and block a pulmonary artery. More than 90% of the cases of pulmonary embolism are a complication of deep vein thrombosis, which typically occurs in patients who have had orthopedic surgery and in patients with cancer and other chronic illnesses like congestive heart failure.

When an embolus plugs a blood vessel, the tissues that are bathed by the blood in the vessel will die when the blood supply is cut off. Death of tissue resulting from the lack of blood is called an infarct. If the embolism is in a coronary artery and the infarct is in the heart muscle it is a heart attack. The seriousness of the attack is determined by which vessel the clot blocks and how much of the heart muscle is infracted (that is, the deadening of the muscle as a result of loss of blood).

The same situation applies to other organs. A cerebral embolism can cause brain damage and bring about a stroke. A pulmonary embolism causes damage to the lung tissue that can be serious. Any of these embolisms can be fatal and must be treated quickly.

An embolism can be diagnosed through the patient’s history, a physical examination, and diagnostic tests. For coronary emboli, cardiac ultrasound and/or arteriography are ordered. For a pulmonary embolism, a chest x ray, lung scan, pulmonary angiography, electrocardiography, arterial blood gas measurements, and venography or venous ultrasound could be ordered.

Patients with emboli require immediate hospitalization. They are generally treated with clot-dissolving and/or clot-preventing drugs. Thrombolytic therapy to dissolve blood clots is the definitive treatment for a very severe pulmonary embolism. Streptokinase, urokinase, and recombinant tissue plasminogen activator (TPA) are used. Heparin is the anticoagulant drug of choice for preventing formation of blood clots. Warfarin (Coumadin^®), an oral anticoagulant, is sometimes used concurrently and is usually continued after the hospitalization.

What causes most emboli to form is not known. Some may form after surgery if air gets into the bloodstream.