The only question tagged as related to TOE in the cardiology revision section is Question 24 from the second paper of 2007, which asks the candidates to compare and contrast TTE and TOE in the evaluation of cardiac disease. In addition to this application, TOE has been compared to the PA catheter in the assessment of shock  (Question 5 from the second paper of 2003) and to the aortogram in the evaluation of aortic dissection (Question 20 from the first paper of 2005,  again in  Question 13 from the second paper of 2010, and again in Question 24 from the first paper of 2015).

Sources for this information

The college answer to Question 24 from the second paper of 2007  offered a table, which is a reasonable brief list of advantages and disadvantages.  It is offered below in an essentially unchanged form: minor refinements and adjustments were made, which were largely cosmetic in nature. The information regarding the application of one modality versus another in any given clinical setting is derived from the massive 2007 Appropriateness Criteria for Transthoracic and Transesophageal Echocardiography by

A Comparsion of TOE and TTE in the Assessment of Cardiac Disease
Category TTE TOE
Equipment
  • Small scale devices available
  • Bedside apparatus ranges from cheap hand-held probes (sub-$10K ) to professional equipment (ranging $70K- $150K)
  • Probes are easily replaceable when they break, as their cost is small
  • There is no cheap bedside option
  • Bedside apparatus is portable but still large and expensive  (ranging $70K- $150K)
  • Expensive probes need to be carefully protected from such threats as patient's teeth
Time lag to diagnosis
  • Instant diagnosis
  • Slight delay
Need for sedation
  • Usually unnecessay
  • Frequently necessary
Invasiveness
  • Non-invasive
  • Minimally invasive
Absolute contraindications
  • None
  • Severe left-sided rib fractures could be viewed as a relative contraindication
     
  • Oral or oesophageal surgery, anastomosis
  • Oesophageal stricture or diverticulum
  • Severe coagulopathy could be viewed as a relative contraindication
Factors affecting image quality
  • Body habitus
  • Mechanical ventilation
  • Patient position
  • Exposure of chest wall (eg. severe burn, or open chest in cardiothoracic theatre)
  • Most of the time image quality is good; most important factor affecting it is the experience of the operator
Infection control
  • Probe needs to be disinfected with surface-acting disinfectant agents (similar to any other patient contact instrument); it is usually not exposed to patient body fluids.
  • It cannot be subjected to autoclaving.
  • Disposable sleeves are available.
     
  • The probe must be disinfected thoroughly in a manner similar to the disinfection of endoscopy probes, as it is exposed to patient body fluids.
  • Protective sleeves are inappropriate.
  • Most probe designs factor in the need to be subjected to automated cleaning, and tolerate high temperatures.
  • The usual probe turnaround time is 20 minutes under ideal circumstances
Mortality and morbidity
  • Essentially, a benign and consequence-free procedure.
  • The greatest risks are misinterpretation of data (leading to inappropriate management) and inaccurate findings (due to operator inexperience).
  • No formal consent process is usually required (verbal / implied consent is sufficient)
  • Each procedure has a small but non-zero risk of major complications, including oesophageal perforation, endotracheal tube dislodgement, and death.
  • The nasogastric tube is often in the way, and ends up being removed. It then needs to be reinserted, with attendent complications.
  • In the non-intubated patient, the use of sedation carries its own risks.
Focused assessment of the cardiac arrest patient
  • The subcostal view does not interfere with CPR, but is a sub-optimal view.
  • Information derived from peri-arrest TTE is frequently useful and tends to change the management
  • Some prognostic interest: patients with absent LV wall movement are highly unlikely to succeed at ROSC (only ~2.4% will go on to ROSC).
  • Also does not interfere with CPR, but offers much better quality of images.
  • Likely to be the only option in perioperative cardiac arrest
  • Same as TTE, changes management in arrest and can offer some prognostic information.
Assessment of ventricular function
  • TTE is a better modality for assessment of LV and RV function as it includes the true cardiac apex
  • Multiple window directions enhance the ability to assess flow with Doppler
  • The cardiac apex is poorly seen with TOE.
  • There are fewer windows, and Doppler assessment of flow is incomplete
Assessment of aortic dissection
  • Descending and thoracic aorta is either impossible or difficult to image.
  • TOE is the US modiality of choice for aortic dissection
Assessment of valve function
  • Valve function can be assessed to a high degree of accuracy provided image quality is satisfactory.
  • Small vegetations cannot be excluded
  • Valve function can be assessed to a high degree of accuracy
  • Valve images are of sufficiently high quality to appreciate small vegetations
  • This is the modality of choice for infective endocarditis
Assessment of septal defects
  • Grossly, large defects and intracradiac shunts can be appreciated, but their quantitative assessment usually cannot be carried out
  • Intracardiac shunts and septal defects are well imaged. This is the modality of choice for such pathology.
Identification of intracardiac thrombi
  • Large LA and LV thrombi can be identified; small thrombi cannot be excluded.
  • All sorts of intracardiac thrombi can be identidfied; particularly the left atrial appendage is well visualised. This is the modality of choice for pre-cardioversion assessment of embolic risk.

References

Cheitlin, Melvin D., et al. "ACC/AHA/ASE 2003 guideline update for the clinical application of echocardiography." A Report of the American College of Cardiology/American Heart Association Task Force on Practice Guidelines (ACC/AHA/ASE Committee to Update the 1997 Guidelines for the Clinical Application of Echocardiography). American College of Cardiology Foundation and American Heart Association (2003).

Roscoe, Andrew, and Tim Strang. "Echocardiography in intensive care."Continuing Education in Anaesthesia, Critical Care & Pain 8.2 (2008): 46-49.

Douglas, Pamela S., et al. "ACCF/ASE/ACEP/ASNC/SCAI/SCCT/SCMR 2007 Appropriateness Criteria for Transthoracic and Transesophageal Echocardiography⁎: A Report of the American College of Cardiology Foundation Quality Strategic Directions Committee Appropriateness Criteria Working Group, American Society of Echocardiography, American College of Emergency Physicians, American Society of Nuclear Cardiology, Society for Cardiovascular Angiography and Interventions, Society of Cardiovascular Computed Tomography, and the Society for ...." Journal of the American College of Cardiology 50.2 (2007): 187-204.