Question 2

College answer

Not available.

Discussion

The act of helping the trainees structure their answer by offering specific headings is laudable, as without it this question could have easily turned into a trap for people who misunderstood the depth of what is expected (for example, from reading the first sentence, one would not immediately develop the impression that one needs to discuss the risks. 

"Rationale for use" of TOE can probably be interpreted as "scenarios which call for the use of TOE instead of TTE", as that would make the greatest amount of sense. A "rationale for use" which includes all the various applications of cardiac sonography would not be a sensible way to answer. Thus:

• Superior resolution for imaging posterior cardiac structures
• Does not interfere with CPR
• Does not require an intact chest wall (thus, suitable for assessing patients with severe anterior chest wall burns, extensive rib fractures, and patients following cardiac surgery).

Data obtained

• Stuctural data:
  • Intracardiac shunts and septal defects
  • Valve structure and function
  • Vegetations
  • Aortic dissection
  • Intracardiac thrombus
  • Guidance for procedures, eg. ECMO cannula positioning
• Functional data:
  • Some contractility and systolic function data (though TTE is better for this)
  • Preload sensitivity (respiratory phasic size variation of the SVC)
  • Shunt flow 
  • Doppler analysis of pulmonary venous inflow
  • Cardiac tamponade effects
  • Cardiac motility and efficacy of resuscitation efforts during cardiac arrest

How it assists clinical management

• Directs haemodynamic management (eg. by identifying fluid responsive patients)
• Directs duration of antibiotic therapy (by identifying vegetation)
• Assesses the success of procedures (eg. TAVI, ECMO cannulation)
• Helps estimate risk of stroke prior to cardioversion of a patient in AF
• Assists decisionmaking in cardiac arrest (where LV wall movement are absent, the patient is  highly unlikely to achieve ROSC).

Associated risks

• 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.

Limitations

• Invasive
• Potential risk of cross-infection
• Probes are expensive and experts who can use them are even more expensive
• Many contraindications, eg. oral or oesophageal surgery, upper GI anastomosis, oesophageal stricture or diverticulum, severe coagulopathy, etc
• TTE is a better modality for assessment of the apex as well as LV and RV function