A transesophageal echocardiogram, or TEE (TOE in the United Kingdom and other countries such as Australia and New Zealand, reflecting the British English spelling transoesophageal), is an alternative way to perform an echocardiogram. A specialized probe containing an ultrasound transducer at its tip is passed into the patient's esophagus. This allows image and Doppler evaluation which can be recorded. It is commonly used during cardiac surgery and is an excellent modality for assessing the aorta, although there are some limitations.
It has several advantages and some disadvantages compared with a transthoracic echocardiogram (TTE).
Specialty medicine professional organizations recommend against using transesophageal echocardiography to detect cardiac sources of embolization after a patient's health care provider has identified a source of embolization and if that person would not change a patient's management as a result of getting more information. Such organizations further recommend that doctors and patients should avoid seeking transesophageal echocardiography only for the sake of protocol-driven testing and to agree to the test only if it is right for the individual patient.
The advantage of TEE over TTE is usually clearer images, especially of structures that are difficult to view transthoracically (through the chest wall). The explanation for this is that the heart rests directly upon the esophagus leaving only millimeters that the ultrasound beam has to travel. This reduces the attenuation (weakening) of the ultrasound signal, generating a stronger return signal, ultimately enhancing image and Doppler quality. Comparatively, transthoracic ultrasound must first traverse skin, fat, ribs and lungs before reflecting off the heart and back to the probe before an image can be created. All these structures, along with the increased distance the beam must travel, weaken the ultrasound signal thus degrading the image and Doppler quality.
In adults, several structures can be evaluated and imaged better with the TEE, including the aorta, pulmonary artery, valves of the heart, both atria, atrial septum, left atrial appendage, and coronary arteries. TEE has a very high sensitivity for locating a blood clot inside the left atrium.
TEE has several disadvantages, although they should be weighed against its significant benefits. The patient must follow the ASA NPO guidelines (usually not eat anything for eight hours and not drink anything for two hours prior to the procedure). Rather than one or two technicians, a TEE needs a team of medical personnel. It takes longer to perform a TEE than a TTE. It may be uncomfortable for the patient, who may require sedation or general anesthesia.
Before inserting the probe, mild to moderate sedation is induced in the patient to ease the discomfort and to decrease the gag reflex, thus making the ultrasound probe easier to pass into the esophagus. Mild or moderate sedation can be induced with medications such as midazolam (a benzodiazepine with sedating, amnesiac qualities), fentanyl (an opioid), or propofol (a sedative/general anesthetic, depending on dosage). Usually a local anesthetic spray is used for the back of the throat, such a xylocaine and/or a jelly/lubricant anesthetic for the esophagus. Children are anesthetized. Adults are sometimes anesthetized as well. Unlike the TTE, the TEE is considered an invasive procedure and is thus performed by physicians in the U.S., not sonographers.
In addition to use by cardiologists in outpatient and inpatient settings, TEE can be performed by a cardiac anesthesiologist to evaluate, diagnose, and treat patients in the perioperative period. Most commonly used during open heart procedures, if the patient's status warrants it, TEE can be used in the setting of any operation. TEE is very useful during many cardiac surgical procedures (e.g., mitral valve repair). It is actually an essential monitoring tool during this procedure. It helps to detect and quantify the disease preoperatively as well as to assess the results of surgery immediately after the procedure. If the repair is found to be inadequate, showing significant residual regurgitation, the surgeon can decide whether to go back to cardiopulmonary bypass to try to correct the defect. Aortic dissections are another important condition where TEE is very helpful. TEE can also help the surgeon during the insertion of a catheter for retrograde cardioplegia.
The transesophageal echocardiogram was first invented by Dr. Leon Frazin in 1974 while working at the Loyola University Stritch School of Medicine, Maywood, and Veterans Administration Hospital, Hines, Illinois. His early findings were published in 1976 in Circulation 
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