Intraoperative tranoesophageal echocardiography (ITOE) is a relatively new application of TOE which began in the 1980-90’s, but but has now become firmly established in the operating room, particularly during cardiac anaesthesia.
The ITOE is an ideal perioperative investigation tool as it allows near continuous monitoring of cardiac function during anaesthesia, as well as the high quality of images not impeded by the surgical field or chest opening. In addition to monitoring cardiac function, ITOE is important for confirming preoperative diagnosis, sizing of valves (if not done prep), guiding cannulation (i.e. retrograde cannula into coronary sinus), weaning from bypass, and for detection of intraoperative complications such as LVF or new RWMA, RV failure, cardiac tamponade, or traumatic dissection.
ITOE showing severe MR prior to MVR.
Although there is little direct evidence ITOE improves outcomes, it has been shown to lead to many changs in management, particularly in high risk surgical patients.
The ITOE differs from standard ASE guidelines (see ASE Comprehensive TOE Guidelines 2013 and ASE Basic TOE Guidelines 2013) for several reasons:
- Limited time: it is not always possible to perform a complete study, and for ITOE it is all about speed. A more limited, focussed study may be performed due to time pressures.
- Variable loading conditions: Preload, afterload and contractility can potentially vary a lot during anaesthisia depending on the stage of operation, the drugs used, volume status, and cardiac bypass. For example, regurgitant lesions tend to reduce in size during episodes of hypotension, but can become much more marked with hypertension. Hence it is important to interpret the findings of an ITOE within the context of the patients HD status. It also doesn’t replace standard TOE or TTE.
- Certain artefacts are also common during operations, such as diathermy and intracardiac air.
Diathermy appears as colourful artifacts, that come and go with the buzzing! Care not to mistake them for regurgitant lesions!.
Intracardiac air is a frequent finding after open-heart procedures and may produce arrhythmias and wall motion abnormalities (especially of the inferior wall). This shows a deep gastric view of the LV being completely filled with microbubbles following reperfusion of a lung during lung transplantation.
When performing ITOE, key questions the anaesthetist and surgeons often want to know include:
- Pre bypass left and right ventricular function
- Aortic condition/plaque for aortic cannulation
- AR, and how much. If mild or greater, anterograde cardioplegia meant for the coronary arteries can instead regurgitate through the aortic valve into the LV, causing LV dilation. This can lead to increasing myocardial oxygen requirements and make operating conditions more difficult.
- Mechanism of valvular regurgitation. If not done preoperatively, then the ITOE is critical to identify the mechanism, location, and severity of valvular regurgitation lesions to allow decisions about, for example, mitral valve repair vs replacement.
- Annular size for sizing of valve replacements
- Paravalvular leaks post valve replacement. These are common, and usually close themselves (post protamine reversal of heparin), but can be torrential and life threatening requiring operative repair.
- Post cardiac bypass LV and RV function. Cardiac bypass effects biventricular function and loading conditions, and post pump cardiac function is often reduced. When weaning off the pump, important decisions about how much inotropic and fluid support the native heart will need as it is liberated from the bypass circuit.
A mid oesophageal 3d short axis view through aortic valve showing severe aortic stenosis prior to replacement.
In addition for the above uses, ITOE may add additional support in complex non cardiac surgery, in thoracic dissection and aortic and hepatic surgery, congenital heart disease, and in hypertrophic cardiomyopathy.
See also: Transoesophageal Echocardiography
