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A transesophageal echocardiogram (TEE; also spelled transoesophageal echocardiogram; TOE in British English) 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).

Details

thumb|Transesophageal echocardiography diagram

TEE is a semi-invasive procedure in that the probe must enter the body but does not require surgical (i.e., invasive) cutting for this procedure.

Before inserting the probe, mild to moderate sedation is induced in the patient to ease the discomfort and to decrease the gag reflex.

Usually a local anesthetic spray (e.g., lidocaine, benzocaine, xylocaine) is used for the back of the throat or as a jelly/lubricant anesthetic for the esophagus.

Sedation and anesthesia are required to make the procedure tolerable and safer, as biting the probe, coughing, vomiting, and patient movement would drastically reduce the value of the procedure.

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).

Children are anesthetized. Adults are sometimes anesthetized as well if moderate sedation is unsuccessful.

Due to the procedure being invasive, sonographers do not perform this procedure unlike transthoracic echo.

Once adequate sedation and anesthesia are achieved, the probe is passed through the mouth and into the esophagus.

From here, the protocol used for the procedure is highly variable.

As the study could be terminated any second (e.g., respiratory compromise, hypotension, intolerance to the probe) the structures of particular interest could be visualized first. For example, if the TEE is ordered to look for

mitral regurgitation then the mitral valve may be fully inspected first. At the completion of the study, the probe is removed and patient is monitored for recovery from sedation.

Advantages

The advantage of TEE over TTE is usually clearer images, especially of structures that are difficult to view transthoracically (through the chest wall). This difficulty with TTE is exemplified with obesity and COPD, as both of these can drastically limit both the window available and the quality of the images obtained through those windows. 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 is also frequently used concurrently with cardiac surgery to provide immediate visualization, inspection, and monitoring of the patient throughout the procedure. Its intraoperative utility includes real-time hemodynamic monitoring by the cardiac anesthesiologist, evaluation of relevant cardiac pathologies before and after surgical repair, and immediate assessment of the success of surgical interventions after cardiopulmonary bypass. TEE can also evaluate for unintended complications from surgery, for example unintended injury to cardiac valves, the aorta, or other structures during the procedure.

Disadvantages

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 sonographer, a TEE needs a team of medical personnel of at least one nurse to monitor/administer sedation and a physician to perform the procedure (a third physician/sonographer can be used to push buttons on the ultrasound machine). It takes longer to perform a TEE than a TTE. It may be uncomfortable for the patient, who may require general anesthesia at the extreme to perform a TEE safely. Due to being an invasive procedure often involving sedation, it is more technically difficult to perform and requires experience to do it well while maintaining safety.

TEE is limited to available anatomy. For example, if the patient has esophageal varices, esophageal stricture, Barrett's esophagus, or other esophageal or stomach problems then this can increase the risk of a TEE significantly.

Performing an esophagogastroduodenoscopy (EGD) beforehand may be necessary to visualize the anatomy for safety, which exposes the patient to a second procedure.

The anatomy may result in prohibitive risk.

With transthoracic echo, numerous measurements are taken to aid in diagnosis and grading of diseases.

These normal ranges are not as well defined for TEE and so there is less accepted standards (e.g., left atrial enlargement).

Some risks are associated with the procedure, such as esophageal perforation around 1 in 10,000, and adverse reactions to the medication.

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.

Diseases

While TEE can be used to answer many questions that a transthoracic echo can answer, the TEE is used for some diseases in particular.

  • Infective endocarditis to get better quality images of the affected valve and better plan surgery, or need for surgery
  • Aortic root abscess, which generally is not visible on transthoracic echo
  • Eccentric mitral regurgitation can be better appreciated on TEE due to Coandă effect
  • Left atrial appendage thrombus and evaluation, follow up, and insertion of a left atrial appendage occlusion device
  • Evaluation for patent foramen ovale and atrial septal defect after a stroke, and insertion of a PFO/ASD plug
  • Monitoring during a procedure to cross the interatrial septum safely without poking the needle through an undesired structure
  • During cardiothoracic surgery for numerous procedures including immediately before and after replacement of a valve

References

  • Virtual TEE – online interactive learning resource
  • TEE online simulator, interactive