Transesophageal echocardiogram

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.[3]

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. (Ref: https://www.asecho.org/wp-content/uploads/2014/05/2013_Performing-Comprehensive-TEE.pdf)

TEE has several disadvantages, although they should be weighed against its significant benefits. The patient must follow the ASA NPO guidelines[4] (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 requiring 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[5] around 1 in 10,000,[6] 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.[7] 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.[7]

Most TEE probes contain a two-dimensional ultrasound crystal. This permits rotation of the 2-D echo plane without physical movement of the probe. This is often referred to the "angle" and varies between 0° and 180° (flipped image of 0°). For any given position of the probe in the body, different angles permit viewing structures more optimally.

The angle can be adjusted with buttons or a dial, and this varies with the specific probe and ultrasound machine.

The probes often have one or two degrees of freedom:

• Flexion or retroflexion can point the crystal superiorly or inferiorly, respectively
• Left and right flexion tilts the probe left and right

These two degrees are typically adjusted using dials on the handle of the probe. A third degree is axial rotation of the probe (clockwise or counter-clockwise) and is present regardless of the other two degrees of freedom. A fourth degree is the translation of the probe long its axis to permit passing through the mouth, into the esophagus, and into the stomach.

The combination of these four degrees of freedom permit 2-D, color, and Doppler echo of practically every structure in the heart.

The midesophageal view is positioned posterior from the left atrium and at 0° this provides for a long-axis four chamber view.

At 0°, the long-axis four chamber view can be obtained with slight retroflexion of the probe. However, slight rotation and insertion may be needed to better visualize the right heart and tricuspid valve.

At 45°, the short-axis view of the aortic valve can be obtained. At this angle, a short-axis view of the right ventricle can be seen to visualize the right atrium, tricuspid valve, right ventricle, and pulmonary valve in a single view.

At 90°, the probe can be rotated clockwise to obtain the "bicaval view" in which the right atrial and both the inferior and superior vena cava can be viewed.

At 135°, the long-axis view of the aortic valve can be obtained.

The left atrial appendage, with proper probe positioning, can be visualized at all angles and often visualized at 0*, 45°, 90°, and 135° to adequately rule out a thrombus.

• 
  0° four chamber
• 
  45° aortic valve short-axis
• 
  90° two chamber
• 
  135° aortic valve long-axis

Pushing the TEE probe past the gastroesophageal junction into the stomach and flexing the probe (pointing it toward the superior) yields a short-axis view of the heart.

At 0°, the short-axis of the left ventricle can be obtained to see wall motion in the basal, mid, and distal sections.

If the probe is rotated clockwise, then the right heart and tricuspid valve can be visualized.

It is in the transgastric position that is best used to quantify the aortic valve with pulse- and continuous-wave Doppler as this is the best view to be best coaxial with the valve.

Pulling back of the TEE probe higher into the esophagus reveals the aortic arch. Typically, in the midesophageal view the probe is rotated until the descending aorta is visualized. Pulling back the probe permits visualization of the aorta and any atheromatous plaques within the aorta. Short axis visualization at 0° allows for descending aorta size measurements. Further pulling back will eventually reach the aorta arch and clockwise rotation will bring the arch into view. Continuous visualization of the aorta to the arch level can visualize coarctation of the aorta.

• 
  Aortic arch