Perioperative transoesophageal echocardiography: past, present & future

Transoesophageal echocardiography (TOE) has transformed the lives of cardiac anaesthetists. Whilst historically respected by their peers, they always remained in the shadow of the cardiac surgeon. The surgeon has always been able to detect aortic atheroma just by feeling the aorta, pronounce on left ventricular function by looking at the right ventricle, and assess the adequacy of mitral valve repair, despite cardioplegia-induced asystole. If the anaesthetists wanted TOE to play with and use for teaching that was fine, but acquiring images of what the heart was actually doing in real time was irrelevant. Over time, the magic wand of TOE has brought about a transformation in which the cardiac surgeon and anaesthetist now work as a team of equals in assessing the patient intra- and postoperatively. In our institution, the cardiac surgeons have changed so radically that they will now not operate without reliable peri-operative TOE. They (and we) also require that TOE is available postoperatively to assess the patient with unsatisfactory haemodynamics who has not responded to simple corrective measures. Many studies report changes in either surgical or medical management as a result of peri-operative TOE. Changes to the surgical plan have been reported in up to 27% of cases before bypass, and in 2% after bypass. There is a significant incidence of new findings that have been missed in the preoperative assessment 1-5. The audit of Skinner et al., in this issue of Anaesthesia, shows that despite what appears to be an adequate work-up, intra-operative TOE unearths new findings in 6% of cases and changes the surgical plan in 68% of these: 4% of cases overall 6. Interestingly, 50% of Skinner et al.’s new findings were unrelated to the listed pathology. We find it disturbing that in 46 patients who had had a pre-operative echocardiogram, and who had unexpected new intra-operative TOE findings, the discrepancy was due to an error in the pre-operative study in 20 (44%). Errors were defined as either an inadequate pre-operative echocardiogram dataset, or misinterpretation of the images. In a further 14, limitations of transthoracic echocardiography (TTE) accounted for the discrepancy. Like Skinner et al., we too have experienced patients who have been misdiagnosed or in whom disease progression has changed the findings. Examples of this include significant aortic stenosis discovered during routine coronary surgery, and significant tricuspid regurgitation discovered during routine mitral repair surgery. It is important to remember that TOE almost always gives clearer images than TTE. This is particularly the case in a patient with poor TTE windows. It is also worth mentioning that it is easier to get good quality TOE pictures, particularly the transgastric views, in an anaesthetised patient than in one undergoing conscious sedation. Transthoracic echocardiography is generally regarded as superior for assessing the aortic valve gradient as Doppler alignment is easier to achieve. It is accepted that intra-operative TOE underestimates the severity of mitral regurgitation, and this assessment should be done by TTE or TOE pre-operatively. However, intra-operative volume loading plus vasopressors to increase systolic pressure has been shown to reflect the true degree of regurgitation. Mitral regurgitation can also be underestimated pre-operatively by TTE under resting conditions or when sedated for TOE 7, 8. Ideally, TTE should be performed with exercise as this is more clinically relevant. Then there is the consideration of consent, or lack of it, upon which both Skinner et al. and Klein et al. touch. Can one commit a patient, for example, to lifelong warfarin therapy or a potential re-operation in the future, by adding a valve replacement without counselling? Should we be telling patients pre-operatively that in the event of a new discovery, we will do what is necessary, or should we give them the option of being woken up without undergoing the additional procedure – a decision that has clinical, psychological and financial implications? Patients may also have preconceived ideas about their procedure and unanticipated changes to surgery might impede their attitude to recovery. Such issues could largely be avoided by performing pre-operative TTE or TOE in every case. However, Skinner et al.’s findings suggest this will not entirely resolve the problem, and there is cost associated with performing pre-operative echocardiography in every patient. Peri-operative TOE is now undertaken in the majority of centres in the UK, Europe and the USA. Until recently, category-1 indications for intra-operative use were limited to valve repair, congenital lesion repair, hypertrophic obstructive cardiomyopathy, endocarditis and aortic dissection. Coronary artery surgery for patients with poor ventricular function was a category-2b indication 9. Recent recommendations from both European and American bodies have indicated that TOE should be used in all elective and emergency cardiac operations unless contraindicated and have upgraded the use in coronary artery surgery to 2a 10-12. The results of Skinner et al.’s study, and the other studies mentioned, further support its routine use in all cases where there isn’t a contraindication, because of the common occurrence of significant new pre-bypass TOE findings that influence the surgical plan. It is notable that in both Skinner et al.’s and Klein et al.’s studies, TOE was utilised in only 40–45% of cases, and was presumably largely restricted to the then category-1 and -2a indications. We suspect that re-audit in 2012 would reveal far higher rates of use. In addition to pre-bypass diagnosis, TOE provides assistance after bypass. It provides a rational basis for decision making during weaning from bypass, chiefly the need for inotropes and vasopressors, intra-aortic balloon pumps, and volume replacement. It allows assessment of the adequacy of surgery, including adequacy of valve repair, prosthesis performance and paravalvular leaks in valve replacements, and wall motion abnormalities in both on- and off pump coronary artery surgery. In our opinion, the increasing age and comorbidity of patients undergoing valvular and revascularisation procedures makes TOE an invaluable asset as part of our monitoring armamentarium. It allows us to fill the patient optimally and relate optimal function to a value of central venous or pulmonary artery pressure that we can then use on the intensive care unit. This is particularly important in hypertensive patients and those with ventricular dysfunction, whether systolic or diastolic, in whom venous pressure does not reflect intracardiac volume 12-15. Transoesophageal echocardiography is the investigation of choice on the cardiac intensive care unit (and general units are catching on) as a diagnostic tool for the haemodynamically unstable patient; a category-1 indication. It is invaluable in determining the cause of haemodynamic failure and it has taught us much we did not previously realise. Among other things it has taught us to appreciate the fragility and afterload sensitivity of the right ventricle, that left ventricular outflow tract obstruction is common and can occur in otherwise normal hearts, and that hypovolaemia can occur in the presence of a high central venous pressure 16-18. The pulmonary artery catheter, although out of favour, should not be discarded just yet: TOE provides an assessment of filling that can be related to the pulmonary artery pressure but using TOE to measure pulmonary artery wedge pressure may be inaccurate 19. Transoesophageal echocardiography allows targeted early re-operation for cardiac tamponade, while decreasing the number of unnecessary re-operations for medical causes of hypotension. This has implications for both patients and trust finances, the latter important in the present climate 13, 20. The development of a disposable probe designed for 48 hours of continuous use will, we think, be very helpful for the development of TOE as a ‘routine’ monitor on intensive care units. Accurate diagnosis is essential if the patient is to receive the correct operation the first time and avoid further surgery later. Pre-operative misdiagnosis results in modification of surgery, often without consent. Whilst the traditional role of the anaesthetist is not as a diagnostician, we have become exactly that. Anaesthetists now make decisions during the procedure that result in changes to the operative plan. It is imperative that one can back up findings that lead to a change of surgery with objective evidence of training and experience; this is a governance issue. Changing surgeons’ minds when they have planned a procedure is not an easy task and it is not undertaken lightly! The introduction of real-time three dimensional (3D) TOE is a significant addition to the diagnostic armamentarium. In assessing the mitral valve there is no doubt that it adds valuable information, especially for the surgeon who can understand the pictures! In transcutaneous aortic valve implantation and Mitraclip® insertion, the spatial assessment that 3D TOE allows is invaluable. Quantification of regurgitation and localisation of residual regurgitation after valve repair or replacement are areas in which 3D is superior to 2D. The role of 3D echocardiography in evaluating the left ventricle has not been as widely accepted, though evidence shows it is more accurate and removes some of the geometrical assumptions behind 2D assessment 21. Three dimensional assessment of the left ventricle is time-consuming and requires sequential beat analysis with ventilation interrupted during acquisition, but it provides more reproducible and accurate assessment of left ventricular volumes and ejection fraction than 2D. Right ventricular volume reconstruction with TTE and TOE shows promise, but is not yet readily available for TOE. Though 3D equipment is more expensive, the cost may decrease with time and more widespread use. Further training in 3D echocardiography is required, even for 2D experts. Current recommendations are that 3D TTE and TOE should be routinely incorporated into assessment of the mitral and aortic valves, including all interventional procedures on either valve, and for left ventricular volume and ejection fraction assessment 22. This leads us on to the importance of training. Miller et al. published a study emphasising the need for training, showing that it improves accuracy of reporting regardless of the sonographer’s base speciality 23. We now have a UK examination in peri-operative TOE which was instituted in 2003 as a result of collaboration between the Association of Cardiothoracic Anaesthetists (ACTA) and the British Society of Echocardiography (BSE). There is also a European examination which ACTA has set up with our European counterparts, EACTA 24. In addition, there is collaboration between ACTA, BSE and the Intensive Care Society to institute a formal training programme and examination for intensivists 25. Training competencies are in the process of being agreed upon, and accreditation will be based on TTE with basic and advanced levels. In every case, there is a balance of risks to be assessed. The risk of major complications, notably perforation of the oesophagus, is between 1:1000 and 1:10 000. No deaths have been reported from this in the literature to date. Minor complications, e.g. sore throat and odynophagia, are common and can be minimised by using a laryngoscope for placement 26-29. A recent study by Tan et al. demonstrates that there is a significant increase in tracheal cuff pressure after insertion of the TOE probe and recommends routine monitoring of cuff pressure after insertion 30. The only absolute contraindication to a TOE in many clinicians’ eyes, ourselves included, is an oesophagectomy 10! In summary, cardiac anaesthetists have developed the use of TOE both in theatre and the intensive care unit. They provide a diagnostic service and training. Peri-operative TOE should compliment accurate pre-operative work up, but should not be a replacement for it. Nevertheless, disease does progress; it is thus inevitable there will always be a small minority in whom new findings occur at surgery. In our opinion, peri-operative 2D and 3D TOE should be used in all cardiac surgical cases, unless strongly contraindicated. No external funding and no competing interests declared.