Transoesophageal Echocardiography

TOE - An Introduction

Stripped of pretension, transoesophageal echocardiography is gastroscopy with attitude! The gastroscope has been extensively modified, with fibreoptic elements replaced by electronic components including an exquisitely engineered ultrasound transducer. However, the controls are still very similar to those of a gastroscope - the most obvious controls are two prominent knobs, the larger of which retroflexes or anteflexes the tip of the probe. The smaller knob is used to provide a little lateral flexion.

The first TOE probes could only visualise the heart in cross section (or "short axis", at ninety degrees to the long axis of the 'gastroscope'); then came biplane probes where the axis of visualisation could be rotated ninety degrees into a "long axis" view. Now we have multiplane probes with the potential for a one-hundred and eighty degree view of the heart.

The major advantage of TOE over the less invasive and less expensive transthoracic echo (TTE) is that much clearer visualisation of the heart is almost always possible with TOE. With TTE, interference is generated by chest wall and lung components. Nevertheless, the two diagnostic modalities should be regarded as complementary rather than sworn enemies - TOE has several limitations, not the least of which is its impaired ability to visualise the ventricles and ventricular outflow tracts in patients with prosthetic valves.

Why do TOE?

Important indications include:

Determination of LV preload intra-operatively, or even in intensive care. TOE is also invaluable in diagnosing the cause of 'acute haemodynamic compromise', especially in the critically ill
Watching for intra-operative myocardial ischaemia
Assessment of the adequacy of a valve repair while the patient is still on the cardiothoracic 'table'.
In addition, the severity of aortic atherosclerosis (atheroma) can be assessed prior to aortic cannulation for cardiopulmonary bypass!
Investigation of a possible cardiac embolic source (notably patent foramen ovale, interatrial septal aneurysm, spontaneous contrast, and intracardiac thrombi)
Assessment of valvular heart disease, particularly native valve disease; this is particularly relevant in the critically ill patient with possible infective endocarditis. Assessment of regurgitant lesions is perhaps more apt, as assessment of stenosed valves is less reliable. Valvular vegetations that were invisible on TTE are often easily seen. TOE is the investigation of choice in looking for valve ring abscesses complicating infective endocarditis.
Investigation of intra- and para-cardiac masses.
TOE is often the investigation of choice for aortic disease, especially aortic dissection.
In the hands of experts, TOE is invaluable in the assessment of congenital heart disease, both pre- and intra-operatively.
In neurosurgery, TOE can be used to detect air embolism.
Prior to cardioversion, the presence of thrombus in the left atrium can be detected.
Newer uses for TOE are being found, practically on a daily basis.

When is TOE less valuable?

There is much argument about the softer indications for TOE. It should probably not be used for:

Assessment of minor degrees of valvular regurgitation
Definitive quantification of stenotic lesions {?}
Mitral valve prolapse (unless associated with substantial mitral regurgitation)
Assessment of ventricular function or outflow tract assessment in the presence of a non-tissue valve prosthesis.

Contraindications to TOE

The most telling and important contra-indication to TOE is when you should be doing something else, that is, resuscitating the patient! In other words, don't let your enthusiasm for investigation stand in the way of your patient care. (This also applies to that near-anachronistic device, the pulmonary artery catheter).

Other contra-indications include:

The patient who hasn't fasted for four to six hours
Anyone with an unstable cervical spine. Remember that in TOE, you flex the neck to introduce the probe, and this is a sure fire way of 'pithing' a patient with a fractured odontoid peg, or severe atlanto-axial subluxation;
Patients with oesophageal disease. This includes severe oesophagitis, oesophageal strictures, and oesophageal varices. The rare disasters reported with TOE have usually been related to damage inflicted on a patient with oesophageal disease, for example torrential bleeding following inadvisable TOE on someone with advanced oesophageal carcinoma. TOE should not be performed if there is any history of previous oesophageal surgery.
Previous mediastinal irradiation should make you re-assess the indication for TOE. Think hard!
The unco-operative patient. TOE + meshugge patient = a recipe for disaster. Sedation may well make things worse, unless you go the whole hog, and slip in an endotracheal tube, with all that this entails.
It's clearly silly to perform TOE in someone with upper gastrointestinal bleeding, and one should think long and hard before contemplating TOE in a patient who has recently had upper GIT surgery. Remember that you are blindly introducing a firm object into the upper gastrointestinal tract.

TOE Training

Ideally the practitioner should be conversant with upper gastrointestinal endoscopy, with perhaps thirty or forty gastroscopies under their belt! Becoming proficient at TOE up to an expert level requires supervised training for a year or more; a lot of TOE is predicated on profound knowledge of the anatomy of the heart and surrounding structures. The AHA, ASE and ACC all more-or-less agree on these issues. In addition, the practitioner should have hepatitis B vaccination with a documented antibody response.

Probably the most important aspect of training is ongoing, repeated correlation of the TOE with the corresponding anatomy. The practitioner should become intimately familiar with all aspects of cardiac anatomy, and the relationship of the heart to surrounding structures. In the spirit of this injunction, we have tried to relate TOE pictures and anatomy throughout this tutorial, although it isn't of course a substitute for hands-on experience under the supervision of an expert!

The ten rules of TOE

Here are a few 'rules' that we consider fairly important. Feel free to differ! People who perform TEE under general anaesthesia or deep sedation may find some of our rules inappropriate, but we believe that even in such circumstances, they hold good.

The Ten Golden Rules

1. Enlist the patient's help (with good explanation and anaesthesia)

2. Perform a thorough clinical assessment before TOE

3. List what you want to know before the TOE!

4. Only use sedation if you *must* (and you have a pulse oximeter on the patient, and a good lawyer on your side)! Don't let the patient drive for 24 hours after sedation.

5. Work systematically from 'stern to stem', basing your assessment on a thorough knowledge of normal anatomy, and of the host of potential pitfalls!

6. Videotape everything (tapes are cheap, errors are expensive) with sound (for your comments)

7. Tell the patient what's going on, and what went on.

8. Use Doppler sparingly

9. Don't over-assess regurgitation, or under-assess stenosis

10. Correlate with TTE, and then go back and this time take another look at the history!