Transoesophageal echocardiography

A standard transoesophageal echocardiography (TOE, or TEE in US English) is a type of ultrasound using an endoscopic transducer, which is advanced into the oesophagus, offering generally superior visualisation of the great vessels and posterior cardiac structures than the standard transthoracic approach (TTE). TOE is most frequently used in specialities such as anaesthesia, cardiology, and critical care, for evaluation of cardiac and aortic structure.

Terminology

Transducer manipulation is more complex than with a transthoracic probe, and the following terminology defines the adjustments one may make to obtain long, short, and 4-chamber axis images of the heart ⁴:

• movement of the probe from the oesophagus to the stomach is "advancing" (more distal in the gastrointestinal tract) and back to the oesophagus is "retracting"
• in the anteroposterior axis, anterior flexion is "anteflexion" and posterior flexion is "retroflexion"
• manual rotation of the probe clockwise is "turning to the right" and anticlockwise is "turning to the right"
• one may also flex the tip in the coronal plane, which is referred to as "flexing to the right/left" respectively
• the imaging plane, or multiplane angle, can be rotated from 0 degrees to 180 degrees, with movement from lower to higher numerical degrees being referred to as "rotating forward" and higher to lower being "rotating backward"

Indications

Indications for TOE include the evaluation of cardiac and aortic structure and function in situations such as ²:

• transthoracic echocardiography is non-diagnostic (or has a high probability of being non-diagnostic, and is deferred)
  • pathology which involves the left atrial appendage or aorta
    • thoracic aortic dissection
    • intracardiac thrombi
  • prosthetic heart valves
  • paravalvular abscess
  • mechanically ventilated patients
  • chest wall injuries
  • unfavorable body habitus
• perioperative, continuous hemodynamic monitoring
• procedural guidance
  • catheter guidance in extracorporeal membrane oxygenation
• cardiopulmonary failure and circulatory shock
  • rapid assessment of hemodynamics and needs for resuscitation

Contraindications

• oesophageal pathology
  • varices, strictures, bleeding
• coagulopathy
• thrombocytopenia

Procedure

Preprocedural evaluation

Typically performed in an intubated, sedated patient (although examination with the use of topical anaesthesia and low-dose analgesia is possible, with or without the use of opioid adjuncts). A bite block is placed, the jaw mobilised anterocaudally, and the probe is inserted into the oropharynx, guided by either fingers or a laryngoscope ⁸.

Comprehensive protocol

A comprehensive exam utilises four different positions in the alimentary tract; the upper oesophagus, midoesophagus, transgastric, and deep transgastric levels ¹. The midoesophageal level is usually found between 30 and 35 cm from the oropharynx where one may visualise the left atrium in the near field, a common reference point; to find the upper oesophageal position, one retracts until the aortic arch is visualised, whereas advancing to the rugae of the stomach with subsequent anteflexion will bring one to the transgastric position.

Common views from these levels and the multiplane angles which are required to achieve them are as follows (with some relevant anatomical examples):

• midoesophageal position
  • five chamber view (0°)
    • both atria, ventricles, left ventricular outflow tract and aortic valve, mitral and tricuspid valves
  • four chamber view (0°)
  • mitral commissural view (60°)
    • left atrium, mitral valve, left ventricle, posteromedial and anterolateral papillary muscles
  • two chamber view (90°)
    • left atrium, mitral valve, left ventricle (anterior and inferior walls)
  • long axis (LAX) view (120°)
    • left ventricle (anteroseptal and inferolateral walls), aortic and mitral valves
  • aortic valve (AV) long axis view
    • sinuses of Valsalva, ascending aorta (1 cm past the sinotubular junction)
  • ascending aorta LAX view (90°)
    • right pulmonary artery, ascending aorta
  • ascending aorta SAX view (0°)
    • ascending aorta, right pulmonary artery, superior vena cava
  • right pulmonary vein view
  • aortic valve (AV) SAX view (30-45°)
    • aortic valve, coronary ostia
  • right ventricular (RV) inflow-outflow view (75°)
    • right atrium, tricuspid valve, right ventricular outflow tract, pulmonic valve
  • bicaval view (90-100°)
    • requires rotation to the right from e.g. a two chamber view
    • interatrial septum, right atrium, superior vena cava, inferior vena cava
  • left atrial appendage view
• upper oesophageal position
  • aortic arch long axis (LAX) view (0°)
    • proximal and distal arch
  • aortic arch short axis (SAX) view (90°)
    • aortic arch, pulmonic valve, main pulmonary artery
• transgastric position
  • basal short axis (SAX) view (0°)
    • left ventricle, mitral valve and commissures
  • mid short axis view (0°)
    • left ventricle, papillary muscles
  • long axis (LAX) view (120°)
  • two chamber view
    • left ventricle (inferior and anterior walls)
  • right ventricular inflow view
    • tricuspid valve, right ventricle (anterior and posterior walls)
• deep transgastric position
  • long axis view (0°)
    • left ventricular outflow tract, aortic valve

Focussed protocols

Abbreviated protocols using a select number of the above views are used in different settings, including basic perioperative evaluation and hemodynamic instability in a critically ill patient. These protocols include:

• the basic perioperative transoesophageal exam (PTE) 
  • scope of practice limited to non-diagnostic monitoring within the customary practice of anaesthesia ⁵
  • able to recognise specific diagnoses that may require advanced imaging skills
• resuscitative transoesphageal echocardiography
  • encompasses the use of TOE in cardiopulmonary arrest
    • also guidance of procedures in the periarrest phase
  • also allows differentiation between shock subtypes, replacing invasive procedures such as catheterization of the pulmonary artery
  • successful use as a point of care exam by emergency physicians for ECMO initiation and in arrest ⁴