Pulmonary Embolism

Topic Overview

What is pulmonary embolism?

Pulmonary embolism is the sudden blockage of a major blood vessel (artery) in the lung, usually by a blood clot . In most cases, the clots are small and are not deadly, but they can damage the lung. But if the clot is large and stops blood flow to the lung, it can be deadly. Quick treatment could save your life or reduce the risk of future problems.

What are the symptoms?

The most common symptoms are:

• Sudden shortness of breath.
• Sharp chest pain that is worse when you cough or take a deep breath.
• A cough that brings up pink, foamy mucus.

Pulmonary embolism can also cause more general symptoms. For example, you may feel anxious or on edge, sweat a lot, feel lightheaded or faint, or have a fast heart rate or palpitations.

If you have symptoms like these, you need to see a doctor right away, especially if they are sudden and severe.

What causes pulmonary embolism?

In most cases, pulmonary embolism is caused by a blood clot in the leg that breaks loose and travels to the lungs. A blood clot in a vein close to the skin is not likely to cause problems. But having blood clots in deep veins (deep vein thrombosis) can lead to pulmonary embolism.

Other things can block an artery, such as tumors, air bubbles, amniotic fluid, or fat that is released into the blood vessels when a bone is broken. But these are rare.

What increases your risk of pulmonary embolism?

Anything that makes you more likely to form blood clots increases your risk of pulmonary embolism. Some people are born with blood that clots too quickly. Other things that can increase your risk include:

• Being inactive for long periods. This can happen when you have to stay in bed after surgery or a serious illness, or when you sit for a long time on a flight or car trip.
• Recent surgery that involved the legs or belly.
• Some diseases, such as cancer, heart failure, stroke, or a severe infection.
• Pregnancy and childbirth (especially if you had a cesarean section).
• Taking birth control pills or hormone therapy.
• Smoking.

You are also at higher risk for blood clots if you are an older adult (especially older than 70) or extremely overweight (obese).

How is pulmonary embolism diagnosed?

It may be hard to diagnose pulmonary embolism, because the symptoms are like those of many other problems, such as a heart attack, a panic attack, or pneumonia. A doctor will start by doing a physical exam and asking questions about your past health and your symptoms. This helps the doctor decide if you are at high risk for pulmonary embolism.

Based on your risk, you might have tests to look for blood clots or rule out other causes of your symptoms. Common tests include blood tests, ultrasound, spiral CT scan, electrocardiogram (EKG), and MRI.

How is it treated?

Doctors usually treat pulmonary embolism with medicines called anticoagulants. They are often called blood thinners, but they don't really thin the blood. They help prevent new clots and keep existing clots from growing.

At first, the doctor may give you a shot of heparin, a blood thinner that works quickly. Then you may take warfarin (such as Coumadin), a blood thinner that you take as a pill. Most people take warfarin for a few months. People at high risk for blood clots may need it for the rest of their lives.

If symptoms are severe and life-threatening, "clot-busting" drugs called thrombolytics may be used. These medicines can dissolve clots quickly, but they increase the risk of serious bleeding. Another option is surgery to remove the clot (embolectomy).

Some people can't take blood thinners, or they form clots in spite of taking the medicine. To prevent future problems, they may have a filter put into the large vein (vena cava) that carries blood from the lower body to the heart. A vena cava filter helps keep blood clots from reaching the lungs.

If you have had pulmonary embolism once, you are more likely to have it again. Blood thinners can help reduce your risk, but they increase your risk of bleeding. If your doctor prescribes blood thinners, be sure you understand how to take your medicine safely, and see your doctor for regular blood tests.

You can reduce your risk of pulmonary embolism by doing things that help prevent blood clots in your legs.

• Avoid sitting for long periods. Get up and walk around every hour or so, or flex your feet often.
• Get moving as soon as you can after surgery.
• When you travel, drink extra fluids. But avoid drinks with alcohol or caffeine.
• Wear compression stockings if you are at high risk.
• If you take blood thinners, take them just the way your doctor tells you to.

Frequently Asked Questions

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Cause

Pulmonary embolism is caused by a blocked artery in the lungs. The most common cause of such a blockage is a blood clot that forms in a deep vein in the leg and travels to the lungs, where it becomes lodged in a smaller lung artery.

Over 95% of blood clots that cause pulmonary embolism are formed in the deep leg veins.¹ Clots also can form in the deep veins of the arms or pelvis.

Occasionally blood clots develop in surface veins, but these clots rarely lead to pulmonary embolism.

In rare cases, pulmonary embolism may be caused by other substances, including:²

• Small masses of infectious material.
• Fat, which can be released into the bloodstream after some types of bone fractures, surgery, trauma, or severe burns.
• Air bubbles from trauma, surgery, or medical procedures.
• Amniotic fluid from normal or complicated pregnancy and childbirth (very rare).
• Tumors caused by rapidly growing cancer cells.
• Foreign substances-such as a catheter that can break off during a medical procedure, talc, mercury, iodine, cotton, or the growth of tapeworm larvae.

Symptoms

The symptoms of pulmonary embolism may include:

• Shortness of breath that may occur suddenly.
• Sudden, sharp chest pain that may become worse with deep breathing or coughing.
• Rapid heart rate.
• Rapid breathing.
• Sweating.
• Anxiety.
• Coughing up blood or pink, foamy mucus.
• Fainting.
• Heart palpitations.
• Signs of shock.

Pulmonary embolism may be difficult to diagnose because its symptoms may occur with or are similar to other conditions, such as a heart attack, a panic attack, or pneumonia. Also, some people with pulmonary embolism do not have symptoms.

See a list of other conditions with similar symptoms.

What Happens

If a large blood clot blocks the artery in the lung, blood flow may be completely stopped, causing sudden death. A smaller clot reduces the blood flow and may cause damage to lung tissue. But if the clot dissolves on its own, it may not cause any major problems.

Symptoms of pulmonary embolism usually begin suddenly. Reduced blood flow to one or both lungs can cause shortness of breath and a rapid heart rate. Inflammation of the tissue covering the lungs and chest wall (pleura) can cause sharp chest pain.

Without treatment, pulmonary embolism is likely to come back.

Complications of pulmonary embolism

Complications of pulmonary embolism may include:

• Cardiac arrest and sudden death.
• Shock.
• Abnormal heart rhythms.
• Death of part of the lung, called pulmonary infarction.
• A buildup of fluid (pleural effusion) between the outside lining of the lungs and the inner lining of the chest cavity.
• Paradoxical embolism.
• Pulmonary hypertension.

Doctors will consider aggressive steps when they are treating a large, life-threatening pulmonary embolism. Death caused by pulmonary embolism usually occurs within 30 minutes of the onset of symptoms.³

Chronic or recurring pulmonary embolism

Blood clots that cause pulmonary embolism may dissolve on their own. But if you have had pulmonary embolism, you have an increased risk of a repeat episode if you do not receive treatment. If pulmonary embolism is diagnosed promptly, treatment with anticoagulant medicines (usually heparin and warfarin) may prevent new blood clots from forming.

The risk of having another pulmonary embolism caused by something other than blood clots varies. Substances that are reabsorbed into the body, such as air, fat, or amniotic fluid, usually do not increase the risk of having another episode. Cancer increases the risk of blood clots.

Having multiple episodes of pulmonary embolism can severely reduce blood flow through the lungs and heart. Over time, this increases blood pressure in the lungs (pulmonary hypertension), eventually leading to right-sided heart failure and possibly death.

What Increases Your Risk

Having a blood clot in the deep vein of your leg and having a previous pulmonary embolism are the two greatest risk factors for pulmonary embolism.

For more information on risk factors for blood clots in the legs, see the topic Deep Vein Thrombosis.

Risk factors for developing clots include having slowed blood flow, abnormal clotting, and a blood vessel injury.

Slowed blood flow

When blood does not circulate normally, clots are more likely to develop. Reduced circulation may result from:

• Long-term bed rest, such as if you are confined to bed after an operation, injury, or serious illness.
• Traveling and sitting for a long time, especially when traveling long distances by airplane.⁴
• Leg paralysis. When you use your muscles, the muscles contract, and that squeezes the blood vessels in and around the muscles. The squeezing helps the blood move back toward the heart. Paralysis can reduce circulation because the muscles cannot contract.

Abnormal clotting

Some people have blood that clots too easily or too quickly. People with this problem are more likely to form larger clots that can break loose and travel to the lungs. Conditions that may cause increased clotting include:

• Inherited factors. Some people have an inherited tendency to develop blood clots that can lead to pulmonary embolism.
• Cancer.
• Heart failure.
• Serious burns.
• Severe infections.
• Use of birth control pills or other medicines that contain estrogen or estrogen-like hormones, such as those some women take for hormone replacement therapy during menopause.²
• Heavy smoking.

Injury to the blood vessel wall

Blood is more likely to clot in veins and arteries shortly after they are injured. Injury to a vein can be caused by:

• Major surgery involving the legs, abdomen, or pelvis.
• A tube (catheter) placed in a large vein of the body (central venous catheter).

Other risk factors include:

• Pregnancy. A woman's risk for developing blood clots increases both during pregnancy and shortly after delivery.
• Age. As people get older (especially older than age 70), they are more likely to develop blood clots.
• Weight. Being overweight increases the risk for developing clots.
• Not taking anticoagulant medicine as prescribed.

When To Call a Doctor

Call 911 or other emergency services immediately if you think you have symptoms of pulmonary embolism. Symptoms include:

• Sudden shortness of breath.
• Sharp chest pain that sometimes becomes worse with deep breathing or coughing.
• Rapid pulse or palpitations.
• Sweating.
• Anxiety.
• A cough that may produce bloody mucus or blood.
• Fainting.

Call your doctor right away if you have symptoms of a blood clot in the leg. These symptoms may include:

• Swelling in a leg that may make it noticeably larger than the other leg. Swelling may also appear as a swollen ridge along a blood vessel that you can feel.
• Skin that is red and warm to the touch.
• Pain or tenderness in the calf or thigh. Some people only notice pain when standing or walking.

Blood clots in the deep veins of the leg are the most common cause of pulmonary embolism. For more information on these types of blood clots, see the topic Deep Vein Thrombosis.

Watchful Waiting

If you think you may have pulmonary embolism, call your doctor or go to the emergency room at the nearest hospital. Watchful waiting is not appropriate for pulmonary embolism.

Who To See

Health professionals who can diagnose pulmonary embolism include:

• An emergency room doctor.
• An internal medicine doctor (internist).
• A family medicine doctor.
• A nurse practitioner or physician assistant.
• A pulmonologist.
• A cardiologist.
• A surgeon. This is most often a general surgeon, an orthopedic (bone) surgeon, or a vascular (vein) surgeon.
• An obstetrician (if pulmonary embolism is pregnancy-related).

To prepare for your appointment, see the topic Making the Most of Your Appointment.

Exams and Tests

Diagnosing pulmonary embolism is difficult because there are so many other medical conditions that can cause similar symptoms, such as a heart attack or an anxiety attack.

Diagnosis depends on an accurate and thorough medical history and ruling out other conditions. Your doctor will need to know about your symptoms and risk factors for pulmonary embolism, such as having recent surgery or having a prior history or family history of blood clots. This information, combined with a careful physical exam, will point to the initial tests that are best suited to diagnose a deep vein thrombosis or pulmonary embolism.

Tests that are often done if you have shortness of breath or chest pain include:

• A chest X-ray. Results may rule out an enlarged heart or pneumonia as a cause of your symptoms. If the chest X-ray is normal, you may need further testing.
• Electrocardiogram (EKG, ECG). The electrical activity of the heart is recorded with this test. EKG results will help rule out a possible heart attack.
• Arterial blood gas analysis. A sudden drop in the blood oxygen level may suggest a pulmonary embolism.

Further testing may include:¹

• D-dimer. A D-dimer blood test measures a substance that is released when a blood clot breaks up. D-dimer levels are usually high in people with pulmonary embolism.
• Spiral (helical) computed tomography. This test is used commonly in most hospitals to check for pulmonary embolism.
• Ventilation-perfusion scanning. This test scans for abnormal blood flow through the lungs after a radioactive tracer has been injected and you breathe a radioactive gas.
• Pulmonary angiogram. A pulmonary angiogram (also called a pulmonary arteriogram) is the most accurate way to diagnose pulmonary embolism. This test is not available at some smaller hospitals and is more invasive than other testing.
• Computed tomography (CT) angiogram. A CT angiogram uses a special dye and a series of X-rays to produce pictures of blood vessels. It can be done to look for a pulmonary embolism or for a blood clot that may cause a pulmonary embolism.
• Doppler ultrasound. A Doppler ultrasound test uses reflected sound waves to determine whether a blood clot is present in the large veins of the legs.
• Echocardiogram (echo). This test detects abnormalities in the size or function of the heart's right ventricle, which may be an indicator of pulmonary embolism.
• Magnetic resonance imaging (MRI). This test may be used to view clots in the deep veins and lungs.

After your doctor has determined that you have a pulmonary embolism, other tests can help guide treatment and suggest how well you will recover. These tests may include:

• A blood test to check the level of the hormone brain natriuretic peptide (BNP). Higher levels of BNP mean your heart is under increased stress.
• A blood test to look at the level of the protein troponin. Higher levels of troponin can mean there is damage to your heart muscle.

Treatment Overview

Treatment of pulmonary embolism focuses on preventing future pulmonary embolism by using anticoagulant medicines. Anticoagulants prevent existing blood clots from growing larger and help prevent new ones from developing.

If symptoms are severe and life-threatening, immediate and sometimes aggressive treatment is needed. Aggressive treatment may include thrombolytic medicines, which can dissolve a blood clot quickly but also increase the risk of severe bleeding. Another option for life-threatening, large pulmonary embolism is surgical removal of the clot, called an embolectomy. This surgery is only available at a few large hospitals.

Some people may also benefit from having a vena cava filter inserted into the large central vein of the body. This filter can help prevent blood clots from reaching the lungs. It is used when anticoagulants are not an option, when clots form despite anticoagulant use, or when there is an increased risk of death or a severely restricted lifestyle if another pulmonary embolism occurs.

Prevention

Daily use of anticoagulant medicines may help prevent recurring pulmonary embolism by stopping new blood clots from forming and stopping existing clots from growing.

The risk of forming another blood clot is highest in the weeks after the first episode of pulmonary embolism. This risk decreases over time. But the risk remains high for months and sometimes years, depending upon what caused the pulmonary embolism. People with recurrent blood clots and/or pulmonary embolism may have to take anticoagulants daily for the rest of their lives.⁵ Anticoagulant medicines also are often used for people who are not active due to illness or injury, or people who are having surgery on the legs, abdomen, or pelvis.⁶

Other preventive methods may also be used, such as:

• Getting you moving shortly after surgery.
• Wearing compression stockings to help prevent leg deep vein thrombosis if you are at increased risk for this condition.

Aspirin may reduce the risk of forming blood clots.⁷ Aspirin, however, is not adequate for treating pulmonary embolism.

You are at higher risk for blood clots when you are traveling because of long periods of inactivity.⁸ To help prevent blood clots during travel:⁹

• Wear compression stockings if you are at risk for deep vein thrombosis.
• Get up and walk around every half hour to an hour.
• Pump your feet up and down by pulling your toes up toward your knees then pointing them down.
• Drink extra fluids.
• Wear loose-fitting clothes that are not tight around your waist or your legs.
• Avoid drinks that have alcohol or caffeine in them, because they cause you to lose fluids. Caffeine is found in coffee, tea, and many sodas.
• Take a dose of low-molecular-weight heparin (LMWH) if your doctor recommends it because you are at high risk for blood clots.

Home Treatment

Home treatment is not recommended for initial treatment for pulmonary embolism. But it is important for preventing additional clots from developing and causing a deep vein thrombosis, which can lead to recurring pulmonary embolism.

Measures that reduce your risk for developing a deep vein thrombosis include the following:

• Exercise. Keep blood moving in your legs by pointing your toes up toward your head so that your calves are stretched, then relaxing. Repeat. This exercise is especially important when you are sitting for long periods of time, for example, on long driving trips or airplane flights.
• Get up out of bed as soon as possible after an illness or surgery. It is very important to get moving as soon as you are able. If you cannot get out of bed, do the leg exercises described above every hour to keep the blood moving through your legs.
• Quit smoking. This is especially important if you are using any medicines that contain estrogen, such as birth control pills.
• Wear compression stockings to help prevent leg deep vein thrombosis if you are at increased risk for this condition.

For more information on how to prevent clots from developing, see the topic Deep Vein Thrombosis.

Medications

Medicines can help prevent repeated episodes of pulmonary embolism by preventing new blood clots from forming or preventing existing clots from getting larger.

Medication Choices

Anticoagulants are prescribed when pulmonary embolism is diagnosed or strongly suspected. Normally, when an injury that causes bleeding occurs, the body sends out signals that cause the blood to clot at the wound. The clot naturally breaks down as the wound heals. A person who is prone to abnormal clotting has an imbalance between clot formation and clot breakdown. Anticoagulants prevent the production of certain proteins that are necessary for blood to clot. Although anticoagulants can prevent new clots from forming and prevent existing clots from getting larger, they do not break up or dissolve existing blood clots.

Heparin and warfarin are the two main types of anticoagulants used to treat pulmonary embolism.

Heparin

Heparin is an anticoagulant given by injection. It immediately affects the clotting system in your body. Oral anticoagulant medicine (warfarin) takes longer to start working.

• Initial treatment with a low-molecular-weight heparin (LMWH) usually is preferred because it can be given as an injection once or twice per day, and it may be given at home, allowing you to leave the hospital earlier. Blood tests are not usually needed to monitor LMWH's clotting effect.
• Unfractionated heparin is another form that can be used. It is given in the hospital. Unfractionated heparin is usually given continuously through your vein (intravenously, or IV), but can also be given as an injection under the skin. Frequent blood tests (usually every 6 hours) are required to monitor the clotting effects of this medicine.¹

Studies show that LMWH is more effective than unfractionated heparin for:¹⁰

• Reducing the risk of another pulmonary embolism.
• Lowering the risk of death 3 to 6 months after starting treatment.

Both forms of heparin can cause severe bleeding in some people. But if bleeding occurs, unfractionated heparin can be stopped quickly, whereas LMWH has to wear off.

Warfarin(such as Coumadin)

Warfarin is an anticoagulant that is taken in pill form. It is usually started while a person is still being treated with heparin because it takes several days for warfarin to build up to a level that's effective. When the warfarin is at a proper level, heparin is discontinued and treatment with warfarin continues. Studies show that warfarin reduces the risk of another blood clot.¹¹

Typically, warfarin is given for at least 3 to 6 months or longer after pulmonary embolism to reduce the risk of having another blood clot. Treatment with anticoagulants may continue throughout your life if the risk of having another pulmonary embolism remains high.

For those people with ongoing risk factors, such as cancer, anticoagulant treatment continues as long as those risk factors are present. Some people with inherited blood-clotting disorders or a history of recurrent deep vein thrombosis or pulmonary embolism may take oral anticoagulants for the rest of their lives.

Because warfarin can increase the risk of birth defects, pregnant women with pulmonary embolism are limited to taking heparin. A few days after the baby is born, a woman can switch from heparin to warfarin.

Thrombolytics

Clot-dissolving (thrombolytic) medicines are not commonly used to treat pulmonary embolism. Although they can quickly dissolve a blood clot, thrombolytics also greatly increase the risk of serious bleeding. They are occasionally used to treat a life-threatening pulmonary embolism.

What To Think About

After pulmonary embolism is diagnosed, a doctor considers:

• Whether anticoagulant medicines are appropriate.
• How long anticoagulants should be used.

If you have recently had a major stroke, surgery, or active internal bleeding, you usually cannot take anticoagulant or thrombolytic medicines. A vena cava filter may help to reduce the risk of another pulmonary embolism in this case.

It's important that you keep the following safety tips in mind when taking warfarin.

Safety tips for anticoagulants

• Take the medicine at the same time each day.
• Check with your doctor before using over-the-counter drugs, especially ones that contain aspirin.
• Tell any new health professionals that you are taking medicine that affects how your blood clots.
• Be alert for signs of bleeding, and call the doctor immediately if any of the following symptoms occur:
  • Blood in your urine, or red stools, or black stools that look like tar
  • Nosebleeds that are hard to stop
  • Spitting up blood
  • New, excessive, or prolonged vaginal bleeding
  • Frequent, severe bruising or tiny red or purple spots on the skin
• Talk to your doctor about medicines you are taking to find out how often you should have blood tests.

If you take warfarin (such as Coumadin):

• Get regular blood tests to ensure that you are taking the right amount of medicine.
• Eat a balanced diet. It is most important to maintain a consistent level of vitamin K foods in your diet. Vitamin K can interfere with the action of warfarin, making it more likely that your blood will clot. For more information, see:

  Anticoagulants: Vitamin K and your diet.

• Avoid excessive use of alcohol. If you drink, do so only in moderation. Chronic drinking may cause liver damage and increase the effect of warfarin.
• Don't use tobacco of any kind.
• Avoid activities that have a high risk for injury, such as skiing, football, or other contact sports. If you are taking warfarin, an injury could result in excessive bleeding.
• Wear a seat belt anytime you are traveling in a car.

Preventing minor bleeding while taking anticoagulants

You may find it helpful to use the following items to lower your risk of bleeding:

• An electric razor
• A soft-bristled toothbrush and waxed floss
• Protective clothing, such as gloves and shoes
• Nonslip mats in the tub and shower

Surgery

Surgical removal of a clot is called an embolectomy. This type of treatment for pulmonary embolism is rarely used. It is considered for people who cannot have other kinds of treatment or those whose clot is so dangerous that they cannot wait for medicine to work. An embolectomy also may be an option for a person whose condition is stable but who shows signs of significant reduced blood flow in the pulmonary artery.

What to Think About

Surgery increases the risk of forming new blood clots that can cause another pulmonary embolism.

Other Treatment

Some people cannot take anticoagulant medicines, or they continue to develop blood clots despite taking the medicines. If surgery or medicines are not options, other methods of preventing pulmonary embolism may be considered, such as a vena cava filter.

Other Treatment Choices

A vena cava filter may be inserted in the large central vein that passes through the abdomen and returns blood from the body to the heart (vena cava). This filter can prevent blood clots in the leg or pelvic veins from traveling to the lungs and heart. These filters may be permanent or removable.

Studies have shown that vena cava filters help prevent pulmonary embolism. But they may be most effective when combined with anticoagulant therapy.

What To Think About

Vena cava filters are not recommended as the first treatment for pulmonary embolism. But they may be considered if you:

• Continue to have pulmonary embolism despite taking anticoagulant medicine.
• Cannot take anticoagulants because of bleeding risk.
• Have an increased risk of death or a severely restricted lifestyle should another pulmonary embolism occur.

Vena cava filters may benefit people who have had a pulmonary embolism surgically removed (embolectomy) if another pulmonary embolism would likely be fatal or severely limit a person's lifestyle.

Vena cava filters can cause serious health problems if they become blocked with one or more blood clots.

Vena cava filters have not been shown to lower the death rate in people with pulmonary embolism.

Other Places To Get Help

Organizations

Related Information

• Deep Vein Thrombosis

References

Citations

1. Tapson VF (2008). Pulmonary embolism. In L Goldman, D Ausiello, eds., Cecil Medicine, 23rd ed., pp. 688-696. Philadelphia: Saunders Elsevier.

2. Task Force for the Diagnosis and Management of Acute Pulmonary Embolism, European Society of Cardiology (2008). Guidelines on the diagnosis and management of acute pulmonary embolism. European Heart Journal, 29: 2276-2315. Available online: http://www.escardio.org/guidelines-surveys/esc-guidelines/GuidelinesDocuments/guidelines-APE-FT.pdf.

3. American College of Obstetricians and Gynecologists (2007). Prevention of deep vein thrombosis and pulmonary embolism. ACOG Practice Bulletin No. 84. Obstetrics and Gynecology, 110(2): 429-440.

4. Lapostolle F, et al. (2001). Severe pulmonary embolism associated with air travel. New England Journal of Medicine, 345(11): 779-783.

5. Buller HR, et al. (2004). Antithrombotic therapy for venous thromboembolic disease: Seventh ACCP conference on antithrombotic and thrombolytic therapy. Chest, 126(3 Suppl): 401S-428S.

6. Kearon C, Hirsh J (2007). Pulmonary embolism section of Venous thromboembolism. In DC Dale, DD Federman, eds., ACP Medicine, section 1, chap. 18. New York: WebMD.

7. Pulmonary Embolism Prevention (PEP) Trial Collaborative Group (2002). Prevention of pulmonary embolism and deep vein thrombosis with low-dose aspirin: Pulmonary embolism prevention (PEP) trial. Lancet, 355(9212): 1295-1302.

8. Abramowicz M, ed. (2006). Advice for travelers. Treatment Guidelines from the Medical Letter, 4(45): 25-34.

9. Hirsch J, et al. (2008). Executive summary: American College of Chest Physicians evidence-based clinical practice guidelines (8th ed.). Chest, 133(6): 71-109.

10. McManus RJ, Fitzmaurice D (2007). Thromboembolism, search date September 2006. Online version of BMJ Clinical Evidence. Also available online: http://www.clinicalevidence.com.

11. Kearon CK, et al. (2003). Comparison of low-intensity warfarin therapy with conventional-intensity warfarin therapy for long-term prevention of recurrent venous thromboembolism. New England Journal of Medicine, 349(7): 631-639.

Other Works Consulted

• Agency for Healthcare Research and Quality (2003). Diagnosis and Treatment of Deep Venous Thrombosis and Pulmonary Embolism. Evidence Report/Technology Assessment No. 68. (AHRQ Publication No.03-E012). Rockville, MD: Agency for Healthcare Research and Quality.

• Fedullo PF (2008). Pulmonary embolism. In V Fuster et al., eds., Hurst's The Heart, 12th ed., pp. 1649-1672. New York: McGraw-Hill Medical.

• Tapson VF, Becker RC (2007). Venous thromboembolism. In EJ Topol et al., eds., Textbook of Cardiovascular Medicine, 3rd ed., pp. 1569-1584. Philadelphia: Lippincott Williams and Wilkins.

• Wood KE (2002). Major pulmonary embolism: Review of a pathophysiologic approach to the golden hour of hemodynamically significant pulmonary embolism. Chest, 121(3): 877-905.

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