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Invited Commentary

Department of Cardiology Royal Melbourne Hospital Grattan Street Parkville 3050, Australia

Intraoperative Echocardiography: An Echocardiographer's Perspective

The article by Morris and colleagues describing Westmead's early experience in intraoperative echocardiography (IOE) is a timely contribution to the current debate in Australia on this topic. Increasingly, anesthetists are using IOE to monitor cardiac performance during critical periods in cardiac operations such as the time of weaning from bypass, in addition to its traditional use in assessing the adequacy of the surgical procedure (usually mitral valve repair). This has raised the obvious questions: (1) when is IOE indicated, (2) who should perform and interpret the IOE, and (3) who takes ultimate responsibility for decision-making based upon the findings?

The organization of echocardiographic services at Westmead is quite different to that at most other Australian cardiac surgical centres in that all echocardiography is performed through the department of nuclear medicine and ultrasound rather than through the department of cardiology. This structure undoubtedly facilitates the training of noncardiologists in echocardiography and assisted in the establishment of their perioperative echocardiography service. It could be argued, however, that the ultrasonic examination of the heart, which is a dynamic pump rather than a macroscopically static structure like most other organs, is best performed and interpreted by those with the best understanding of the nuances of ultrasonic manifestations of cardiac hemodynamics. Such people are not necessarily cardiologists but they should spend a large proportion of their time working solely in echocardiography rather than general ultrasonography.

One of the points raised by cardiac anesthetists in support of their call for increased access to facilities for IOE is that it is invaluable in guiding the weaning from cardiopulmonary bypass of patients with no conventional indication for IOE. The Westmead report actually does not support this proposition. Only 199 of over 700 cases were studied intraoperatively. Ninety-five of these were for coronary bypass grafting alone. Therefore, up to 500 bypass patients were managed without IOE. Unfortunately, no indication is given as to how the 95 were chosen for monitoring by IOE.

Another point of contention is the role of prebypass IOE in the decision-making process for the operation. While the sizing of valve prostheses when no other indication is present for a separate preoperative transesophageal echocardiogram (TEE) is certainly a sensible use of the modality, some of the other indications given really represent an inadequate preoperative evaluation. Last minute decisions contradicting careful preoperative evaluation are usually wrong. Two examples should illustrate this principle.

First, the case of a patient presenting for bypass surgery with mitral regurgitation. It should be possible to adequately assess the severity and etiology by transthoracic echocardiography (TTE). If there is doubt about the severity after TTE, then TEE is indicated rather than prebypass IOE as the severity of functional mitral regurgitation can be altered substantially by the hemodynamic changes associated with anesthesia. In addition, the careful, unhurried assessment of mitral regurgitation by all available echocardiographic modalities avoids precipitous decision-making based solely on the size of the color jet that many operators use as their sole criterion for assessment of regurgitant severity. Not only is this criterion exquisitely sensitive to machine factors, but also to hemodynamic changes, which are at their most profound in the operating room.

Second, the evaluation of incidental aortic stenosis in bypass patients is far better assessed by TTE than IOE or TEE. Although planimetry of the valve can be helpful, Doppler evaluation of the transvalvular gradient is the most useful parameter for patients with all but the most severe left ventricular dysfunction. Steerable continuous-wave Doppler from the transgastric view may achieve adequate alignment with flow to measure a reliable gradient, but this is not possible in all patients due to the confinement of the transducer within the gastrointestinal tract. By contrast, transthoracic assessment of aortic valve gradient utilizes multiple echocardiographic windows to ensure adequate alignment to flow. In my experience, IOE has either confirmed the TTE findings or been incorrect.

Assessment of aortic dissection can be undertaken in the operating room just as well as in the emergency department, but often the information provided by the TEE is required before the decision is made to take the patient to theater. Acute aortic disease is a difficult study and should be performed only by the most experienced operators; be they cardiologist or cardiac anesthetist.

As with the prebypass IOE, the evaluation of the adequacy of a mitral valve repair, septal myomectomy or repair of congenital heart disease is not a job for the occasional operator. The evaluation is often complicated by hemodynamic instability, surgically created ultrasonic artefacts, and pressure for a quick response. While most cases turn out to be straightforward, this is not the time to find that one has been promoted beyond one's level of competence. It is therefore imperative that training and quality assurance measures as well as appropriate back up are in place whenever IOE is to be undertaken, as seems to be the case of Westmead.

One interesting feature of the Westmead experience is their use of automated border detection and Color Kinesis in the assessment of left ventricular function. While the use of these technologies has been well validated (mainly in TTE), they are not always easy to apply in a given patient and are subject to various artefacts. In particular, the assessment of regional wall motion by Color Kinesis cannot correct for translation motion of the heart during the cardiac cycle and may therefore be misleading if the underlying two-dimensional image is not carefully evaluated to exclude this possibility. The drawbacks of this approach are underlined by the fact that it has not become a widely used tool in stress echocardiography where assessment of regional wall motion is the essence of the study. Thus, while automated boundary detection may be a useful adjunct to visual assessment, the reading of a fractional area change measurement from the bottom of the screen cannot yet replace the experienced observer. A more useful aid (again borrowed from stress echocardiography) is to digitally store cineloop that can then be displayed side-by-side with current images for direct comparison.

In Australia, as elsewhere, financial considerations forced upon the medical profession by Government needs to be addressed. The routine use of IOE for bypass surgery will increase the cost of this Medicare item several hundred fold over and above its traditional use. The relatively high Medicare schedule fee pertaining to IOE relates both to the high capital cost of the equipment that is tied up for considerable periods of time and also to the considerable commitment of the cardiologist who must make himself available at short notice for the procedure and who would not otherwise be involved in the operation. This is quite a different situation to the use of IOE by an anesthetist who is already involved and present in the theater. The Federal Government has made it clear that the total funds available for echocardiography are fixed and blowouts in one item number will lead to reductions in the schedule fee for all echocardiographic services. It is, therefore, the position of The Cardiac Society of Australia and New Zealand that a separate item number be established in the anesthetic portion of the schedule for routine monitoring.

There is no doubt that IOE has a great potential to make cardiac surgery safer. In its traditional role, IOE is already established as an integral part of some surgical procedures. It is, however, a demanding discipline and difficulties crop up at unexpected times. It is, therefore, imperative that centers utilizing IOE establish adequate levels of training, quality control, and back up for less experienced operators. Within each institution, the most appropriate operator for the procedure being undertaken must be employed with excellent communication between all members of the team caring for the patient.

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