Transoesophageal Echocardiography
Transoesophageal echocardiography (TOE) uses a miniaturised multiplane 3 to 7 MHz phased array transducer mounted at the tip of a flexible gastroscope like probe. The probe is introduced into the oesophagus and stomach to image the heart and thoracic aorta from behind, with the transducer separated from the heart only by the oesophageal wall.
The close position avoids the chest wall, ribs and lungs, giving high resolution images of posterior structures (left atrium, left atrial appendage, interatrial septum, pulmonary veins, mitral valve, aortic valve and root, prosthetic valves, descending thoracic aorta). Multiplane imaging rotates the image plane from 0 to 180 degrees.
The usual views are mid-oesophageal (four chamber, two chamber, long axis, aortic valve short axis and long axis, bicaval, left atrial appendage), transgastric (short axis of the left ventricle, long axis) and the deep transgastric and aortic views. Three dimensional TOE gives a surgeon's view of the mitral valve.
The patient is under topical pharyngeal anaesthesia with or without conscious sedation (midazolam, with or without an opioid or propofol). The examination takes 15 to 30 minutes, plus preparation and recovery of 1 to 2 hours.
TOE is used when TTE is non-diagnostic or when better visualisation of posterior structures is needed, and in the operating room and interventional laboratory for monitoring and control of procedures. It has a sensitivity of 90 to 100% for left atrial appendage thrombus, over 90% for vegetations (versus 60 to 70% for TTE), and about 98 to 99% for aortic dissection.
The complication rate is low: major complications occur in under 1 in 1000 (oesophageal perforation 0.01%, bleeding, arrhythmia, aspiration, laryngospasm, respiratory depression), and mortality is about 0.01%. Minor complications (sore throat, transient hypotension, mouth or lip injury) are more frequent.
Indications. Suspected infective endocarditis with negative or non-diagnostic TTE, prosthetic valve endocarditis, and suspected abscess or fistula. Source of embolism (left atrial appendage thrombus, patent foramen ovale, atrial septal aneurysm, aortic arch atheroma, valve masses) in unexplained stroke or transient ischaemic attack.
Before cardioversion in atrial fibrillation of unknown duration or inadequately anticoagulated, and before catheter ablation, to exclude left atrial thrombus. Assessment of mitral valve disease and suitability for repair or percutaneous intervention (edge-to-edge repair, balloon valvuloplasty). Prosthetic valve dysfunction (thrombosis, pannus, dehiscence, paravalvular leak).
Suspected aortic dissection, intramural haematoma, traumatic aortic injury, or aortic atheroma (when CT is not possible or the patient is unstable). Congenital heart disease in adults (atrial septal defect, sinus venosus defect).
Control of catheter based interventions (closure of atrial septal defect or patent foramen ovale, left atrial appendage occlusion, transcatheter aortic valve implantation, mitral intervention) and cardiac surgery (pre- and post-bypass monitoring, repair assessment). Intraoperative haemodynamic monitoring in cardiac and high risk non-cardiac surgery.
Unexplained haemodynamic instability in the intensive care unit when TTE is inadequate. Cardiac arrest in selected settings (during resuscitation).
Contraindications and precautions. Absolute: oesophageal stricture, tumour, perforation, laceration, diverticulum (Zenker), recent oesophageal surgery, active upper gastrointestinal bleeding, and an uncooperative patient or an unprotected airway in a patient who cannot be sedated safely.
Relative: oesophageal varices (especially with recent banding), previous oesophagectomy or gastric surgery, radiation to the mediastinum, severe cervical spine disease (atlantoaxial instability), coagulopathy or thrombocytopenia, dysphagia of unknown cause, hiatus hernia (large), and symptomatic or unstable cardiopulmonary conditions. The patient must fast for at least 4 to 6 hours.
Dentures are removed and the history is taken for dysphagia, odynophagia, previous oesophageal disease, and allergy to local anaesthetic and sedation drugs. Written consent is obtained. Monitoring includes pulse oximetry, blood pressure, electrocardiogram, and supplemental oxygen. A bite guard is used. Antibiotic prophylaxis is not routinely needed.
Anticoagulation is checked (the international normalised ratio is not usually needed unless there is a bleeding risk).
Preparation and technique. The patient lies in the left lateral decubitus position. Lidocaine spray or gel is applied to the pharynx, and sedation is titrated for comfort while keeping the patient responsive.
The lubricated probe is passed over the tongue and into the oesophagus with a bite block in place, advancing gently without force (the patient is asked to swallow, and the neck is flexed). Views are obtained in a systematic order, with the transducer advanced and withdrawn and the multiplane angle rotated.
The left atrial appendage is examined at several angles (0, 45, 90 and 135 degrees) for thrombus, spontaneous echo contrast (smoke) and emptying velocity. Bubble contrast (agitated saline) with Valsalva identifies right to left shunting.
The probe is withdrawn after the study with suction of the pharynx, and the patient is monitored until fully awake and then kept nil by mouth until the throat anaesthesia wears off (1 to 2 hours), with an escort for the outpatient.
