What is an embolus? In its most general form an embolus is a mass that travels in the blood stream from one area of the body to another. Emboli are usually small pieces of blood clot.
Once they travel to a small enough vessel, emboli will lodge and prevent further blood flow. One of the most common spots for emboli to lodge is in the blood vessels going from the heart to the lung, aka, the pulmonary arteries and their respective branches.When an emboli lodges in the pulmonary vasculature it is called a pulmonary embolus.
Nearly all pulmonary emboli break off from blood clots in the deep veins of the leg. These "mother" clots are known as deep venous thrombosi.
A significant percentage of pulmonary emboli do not cause any signs or symptoms. Often times they are so small that the rest of the lung is able to compensate for the decreased blood flow.
However, if the pulmonary embolus is large, or there are multiple pulmonary emboli the lung may not be able to oxygenate the blood as well as it normally does. When this occurs the patient may feel short of breath. Some patients have chest pain and a cough. Most patients with significant sized pulmonary emboli have an increased heart rate as well.
If the pulmonary emboli is massive the right side of the heart may have to pump against extremely elevated pressures leading to right heart failure. Abnormal heart rates and death can occur if treatment is not initiated quickly.
It is important to check for leg pain or swelling since most pulmonary emboli come from blood clots in the deep veins of the lower leg. However, some patients with pulmonary emboli may have no symptoms of a blood clot in their lower extremities.
There are two ways to diagnose a pulmonary embolism. The first way is to do a contrast enhanced CT scan of the chest. If a pulmonary embolus is present there will be dark areas in the arteries. These dark areas are a result of contrast flowing around, or being completely blocked by embolus material.
Some patients may not be able to handle the contrast required during the CT scan (ie: patients with renal failure, allergic reactions to iodine, etc). These patients can undergo an alternative study known as a ventilation-perfusion scan.
In this study a radioactive substance is injected intravenously at the same time the patient inhales a radioactive gas. The intravenous component measures arterial perfusion and the inhalational component measures ventilation. Any areas of ventilation and perfusion "mismatch" may represent a region of lung affected by a pulmonary embolus.
An additional blood study that is often ordered is a "d-dimer". D-dimers are fibrin degradation products from blood clots. This test is only useful if there is a low probability of pulmonary embolism; if the result is normal, it essentially rules out a pulmonary embolus. However, an abnormal result is by no means conclusive of a PE, and additional studies (ie: CT or ventilation perfusion scanning) must be done. In other words, a d-dimer test is highly sensitive, but not specific for pulmonary emboli.
Anticoagulation to prevent clots from growing is the mainstay of treatment for pulmonary embolism. For minor pulmonary emboli, subcutaneous low molecular weight heparins like enoxaparin (Lovenox®) or intravenous unfractionated heparin are used to anticoagulate the patient. This is generally followed by at least several months of warfarin (Coumadin®).
The period of time the patient should be on warfarin depends on the etiology of the pulmonary embolism. If the patient has a known risk factor for embolic disease such as trauma or surgery they should be anticoagulated for 3 months. If they have an idiopathic pulmonary embolism (ie: no known reason for the clot) then anticoagulation should be at least 6 months in duration. A recurrence of an idiopathic pulmonary embolus warrants anticoagulation for at least a year.
Patients with massive pulmonary emboli that cause heart failure and/or abnormal heart rhythms should be considered for thrombolytic therapies. The medications commonly used for thrombolysis include alteplase and streptokinase.
Thrombolytic therapy may not be an option in patients with a significant bleeding risk. These patients may have to undergo specialized surgical or mechanical procedures to remove the clot manually.
Pulmonary emboli are blood clots that travel to the vessels in the lung. Most are asymptomatic; however, large or multiple pulmonary emboli can cause shortness of breath, tachycardia (ie: rapid heart rate), cough, right sided heart failure, cardiac arrhythmias and potentially death if left untreated. Diagnosis is based on CT and/or ventilation perfusion scans. Treatment for non-massive pulmonary emboli is anticoagulation with heparin followed by warfarin. Massive pulmonary emboli can be treated with thrombolytic medications, but surgical interventions may also be necessary in some patients.
(1) Kearon C, Kahn SR, Agnelli G, et al. Antithrombotic therapy for venous thromboembolic disease: American College of Chest Physicians Evidence-Based Clinical Practice Guidelines (8th Edition). Chest. 2008 Jun;133(6 Suppl):454S-545S.
(3) Ho WK. Deep vein thrombosis--risks and diagnosis. Aust Fam Physician. 2010 Jun-Jul;39(6):468-74.
(4) McRae S. Pulmonary embolism. Aust Fam Physician. 2010 Jun-Jul;39(6):462-6.
(5) Flynn JA. Oxford American Handbook of Clinical Medicine (Oxford American Handbooks of Medicine). First Edition. Oxford University Press, 2007.
(6) Kumar V, Abbas AK, Fausto N. Robbins and Cotran Pathologic Basis of Disease. Seventh Edition. Philadelphia: Elsevier Saunders, 2004.