How can transesophageal echocardiography (TEE) be used to image non-cardiac mediastinal structures in adult humans?

From the Guidelines

Transesophageal echocardiography (TEE) can be used to image non-cardiac mediastinal structures in adult humans by providing excellent visualization of the posterior mediastinum, including the descending thoracic aorta, pulmonary arteries, lymph nodes, esophageal lesions, and pleural spaces. The procedure involves inserting a specialized ultrasound probe into the esophagus, which allows for high-resolution imaging of these structures due to the proximity of the esophagus to the mediastinum 1. For optimal imaging, the patient should be sedated with medications like midazolam (1-5 mg IV) or propofol (initial dose 0.5-1 mg/kg followed by 25-75 mcg/kg/min) to ensure comfort during probe insertion and manipulation.

Key Considerations for TEE in Mediastinal Imaging

• Various probe positions and imaging planes can be used to visualize different structures: the upper esophageal position for the aortic arch and great vessels, mid-esophageal for lymph nodes and pulmonary vessels, and transgastric for inferior structures.
• TEE offers advantages over transthoracic echocardiography for mediastinal imaging due to the absence of interference from lung tissue and chest wall structures, providing higher resolution images 1.
• However, practitioners should be aware of potential blind spots, particularly in the anterior mediastinum, and recognize that TEE is invasive and requires sedation, making it less suitable as a first-line imaging modality for non-cardiac structures unless cardiac imaging is also needed 1.

Clinical Applications of TEE

• Detection and assessment of aortic dissection and other aortic pathologies
• Evaluation of valvular disorders including prosthetic valve function
• Evaluation of a variety of congenital heart diseases in both children and adults
• Use in patients with suspected cardiac trauma, in critically ill medical or surgical patients with unstable hemodynamics, and in patients whose clinical status necessitates echocardiographic assessment but in whom TTE studies are technically inadequate or non-diagnostic 1.

From the Research

Imaging Non-Cardiac Mediastinal Structures

Transesophageal echocardiography (TEE) can be used to image non-cardiac mediastinal structures in adult humans. The following are some key points to consider:

• TEE is performed in cases of a justified need to visualize structures that are poorly visible or invisible on transthoracic echocardiogram 2.
• Primary indications for TEE include an assessment of the thoracic aorta and other vessels 2.
• TEE can be used to evaluate the left atrium and left atrial appendage for the presence of thrombus prior to cardioversion and pulmonary vein isolation 3.
• TEE has been used in non-cardiac surgery to monitor hemodynamic parameters and to assess volume status, ventricular function, and valvular pathology 4, 5.
• TEE can be used to image non-cardiac mediastinal structures, such as the thoracic aorta, and to assess for pathology such as thrombus or aneurysm 2, 3.

Views and Settings

The following views and settings can be used to image non-cardiac mediastinal structures:

• Low transesophageal view (the probe is advanced approximately 30 cm from the teeth) 2.
• Mid transesophageal view (the probe is advanced approximately 30 cm from the teeth) 2.
• High transesophageal view (the probe is advanced approximately 25-30 cm from the teeth) 2.
• Transgastric subcardiac view (the probe is advanced approximately 35-40 cm from the teeth) 2.
• Transgastric five-chamber view (the probe is advanced deeper than in the subcardiac view and with a stronger anterior flexion of the probe) 2.
• Aortic view (the probe should be rotated at about 180°) 2.

Clinical Applications

TEE has several clinical applications in imaging non-cardiac mediastinal structures, including:

• Evaluation of the thoracic aorta for pathology such as thrombus or aneurysm 2, 3.
• Assessment of volume status and ventricular function in non-cardiac surgery 4, 5.
• Diagnosis of gross valvular pathology and pericardial tamponade 4, 5.
• Monitoring of cardiac output and response to therapy in non-cardiac surgery 4, 5.