Transesophageal Echocardiography

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Transesophageal echocardiography

Definition

Transesophageal echocardiography (TEE) is a diagnostic test in which an endoscope with an ultrasound transducer at its tip is inserted into the patient's esophagus by means of a catheter (thin tube). Sound waves are transmitted and received by the transducer to produce a clear image of the heart muscle and other parts of the heart.

Purpose

Since the esophagus is located directly behind the heart, transesophageal echocardiography provides a very clear image of the heart. It can provide information on the size of the heart, its pumping strength, and the location and extent of any damage to its tissues. TEE can also detect the presence of abnormal tissue growth around the heart valves. It is useful for identifying abnormalities in the pattern of blood flow, such as the backward flow of blood through partly closed heart valves (regurgitation). TEE is especially useful in cases in which conventional echocardiography (a test in which the transducer is moved across the patient's chest) cannot offer a good image, as when the patient is obese or has a thick chest wall. TEE is also used to monitor heart function during cardiac surgery; to detect blood clots in the left atrium of the heart; and to diagnose infections in pacemaker lead infections.

TEE is performed with portable devices and equipment, and it is safer and less expensive than aortography, an invasive procedure performed in a cardiac catheterization laboratory. TEE is less expensive than computed tomography and magnetic resonance imaging , two diagnostic imaging modalities commonly used for cardiac studies; in addition, it allows a more direct evaluation of the heart. Finally, results from a TEE examination are available within 15 minutes, which offers the physician another advantage over CT scans .

The convenience, safety, and promptness of TEE make it the diagnostic procedure of choice in patients suspected of aortic dissection, especially those who are in unstable condition. TEE can also be used for long-term follow-up of these patients.

Precautions

Transesophageal echocardiography should be performed only by physicians who have received the necessary postgraduate training. It is a highly specialized technique requiring advanced skills in interpreting results as well as performing the procedure.

TEE should not be performed in patients with dysphagia (difficulty swallowing), indications of gasteroesophageal disease, or injuries to the esophagus. Before the procedure, the patient should be asked about any drug allergies and current medications, since some medications may entail risks during the procedure. For example, patients on anticoagulant therapy are at risk for bleeding complications.

Patients should avoid consuming alcohol for a day or so before and after TEE, since alcohol may amplify the effects of the sedative used with the procedure.

Description

TEE uses the same principles as conventional echocardiography to produce images of the heart, namely high-frequency sound waves. TEE produces sharper images, however, because the transducer is positioned directly behind the heart, not on the chest wall as in conventional echocardiography.

A TEE examination generally lasts 15–30 minutes. The patient is given a mild sedative intravenously, and the back of the throat is sprayed with a local anesthetic in order to suppress the gag reflex. The patient is positioned on the left side. A special viewing tube called an endoscope, which contains a transducer at the tip, is inserted through the mouth and into the esophagus. The instrument is carefully moved until it is positioned directly next to the heart. Essentially a modified microphone, the transducer directs ultrasound waves into the heart, some of which are reflected (or echoed) back to the transducer. Tissues of different densities and blood all reflect ultrasound waves differently. These sound waves can be translated into an image of the heart, displayed on a monitor, or recorded on paper or tape. The transducer may be moved several times during the test to help the doctors get a better view of the heart.

TEE can be performed as an outpatient procedure in an echocardiography laboratory; as an inpatient procedure in an operating room; or as an emergency procedure in an intensive care unit or emergency department.

Preparation

The patient is asked not to eat or drink for six hours before the TEE examination. Patients who wear dentures must remove them before the test. The patient may be given a mild sedative intravenously before the procedure, and an anesthetic is sprayed into the back of the throat in order to suppress the gag reflex.

Aftercare

After the test, the patient must refrain from eating or drinking until the gag reflex has returned—otherwise, he or she may accidentally inhale some of the food or beverage. In addition, patients should not drive or operate heavy machinery for at least 10–12 hours if they have been given a sedative. They should avoid consuming alcohol for a day or so, since alcohol may amplify the effect of the sedative.

KEY TERMS

Aneurysm —A dilatation of the aorta or other artery, caused by a weakening of the vessel wall.

Aorta —The main artery of the circulatory system, conveying blood from the left ventricle of the heart.

Dissection —Separation of the layers of arterial tissue in the aorta, resulting from blood being forced out into the wall of the aorta through a tear in the innermost layer of tissue.

Dysphagia —Difficulty in swallowing.

Endoscope —An instrument used to visualize and examine the inside of a body cavity or organ.

Gag reflex —A normal reflex consisting of elevation of the palate, retraction of the tongue, and contraction of the throat muscles.

Regurgitation —The backward flow of blood through a partly closed valve.

Transducer —A device that converts electrical signals into ultrasound waves and the echoes back into electrical impulses.

Ultrasound —Sound waves at a frequency of 2–10 megahertz (mHz), often used for diagnostic imaging.

Complications

Transesophageal echocardiography may cause gagging and discomfort when the endoscope is inserted down into the throat. Patients may also experience a sore throat for a few days after the test. In rare cases, the procedure may cause bleeding or perforation of the esophagus, or an inflammatory condition known as infective endocarditis . The patient may also have an adverse reaction to the sedative or local anesthetic.

Results

A normal transesophageal echocardiogram shows a normal heart structure and normal patterns of blood flow through the valves and chambers of the heart.

In terms of abnormal findings, a transesophageal echocardiogram may show a number of abnormalities in the structure and function of the heart, such as thickening of the wall of the heart muscle (especially the left ventricle). Other abnormal findings may include aneurysms or dissections of the aorta; regurgitation; or blood clots in the left atrium of the heart.

Health care team roles

TEE is performed by a cardiologist trained and experienced in the applications of cardiac sonography. A cardiac ultrasonographer may assist during the procedure. Nurses are present during TEE to monitor the patient's vital signs . During cardiac surgery, TEE may be performed by the cardiac surgeon or by a cardiovascular anesthesiologist.

Resources

BOOKS

Faculty Members of the Yale University School of Medicine. The Patient's Book of Medical Tests. Boston and New York: Houghton Mifflin Company, 1997.

PERIODICALS

Lopez-Candales, Angel. "Assessing the Aorta with Transesophageal Echocardiography: Update on Imaging Capabilities with Today's Technology." Postgraduate Medicine 106, no. 4 (October 1, 1999): 157-172. Available online at <http://www.postgradmed.com/issues/1999/10_01_99/lopez.htm>.

Report by the American Society of Anesthesiologists and the Society of Cardiovascular Anesthesiologists Task Force on Transesophageal Echocardiography. "Practice Guidelines for Perioperative Transesophageal Echocardiography." Anesthesiology 84 (1996): 986-1006.

Rose, Verna L. "American College of Cardiology and American Heart Association address the use of echocardiography." American Family Physician 56 (October 7,1997): 1489-90.