Transesophageal echocardiography and adult cardiac operations

CURRENT REVIEW

Transesophageal Echocardiography and Adult Cardiac Operations Alan J. Bryan, FRCS, Benico Barzilai, MD, and Nicholas T. Kouchoukos, MD Divisions of Cardiothoracic Surgery and Cardiology, Washington University School of Medicine, St Louis, Missouri

Transesophageal echocardiography (TEE) now is used widely as a monitoring technique during and after cardiac operations. Widespread adoption of the technique has provided a wealth of new information. This review analyzes the influence of TEE on the routine conduct of cardiac operations and on surgical decision making in specific areas. Its use in routine hemodynamic monitoring and problem solving, both intraoperatively and postoperatively, is discussed. Transesophageal echocardiography has a particular role in valve operations, in guiding

and assessing the immediate results of mitral valve repair. It also has found application in the grading and operative management of the severely atheromatous aorta, the diagnosis and management of aortic dissection, and other aspects of surgery of the thoracic aorta. In addition, management in specialized areas, such as cardiopulmonary transplantation and the insertion and monitoring of ventricular assist devices, have also been helped by the information provided by TEE.

n the past 10 years transesophageal echocardiography Iclinical (TEE) has developed rapidly, leading to its wide application [1, 2]. It is being used with increasing

isfactory for various reasons including the presence of chronic pulmonary disease, obesity, and, in particular the early postoperative period, the presence of chest tubes [7]. In contrast, with probe positioning before the commencement of the operation, TEE can be used to monitor the entire operative procedure with some element of consistency and without interruption of the surgical procedure or the sterile field [3]. In addition, postoperatively in the intensive care unit transesophageal echocardiography usually offers substantial advantages over transthoracic echocardiography from the point of view of image quality [7]. The potential limitations of TEE have lessened rapidly with technologic advances and the development of probes that incorporate color flow Doppler and biplane and multiplane imaging [1, 8]. However, imaging of the distal ascending aorta, which is screened by the trachea, and imaging of the left ventricular apex may be suboptimal [3]. In addition, there remains limited ability to quantify precisely valvular regurgitation or ventricular function without deriving ventricular volumes from complex geometric modeling [9]. The actual risks associated with the procedural aspects of TEE appear to be small [2], although attention should be paid to potential hazards associated with preexistent esophageal pathology [1]. The risk of esophageal perforation and bacteremia is small [10]. Any detrimental effects of prolonged concomitant endotracheal and esophageal intubation on pharyngeal or esophageal motor function are not quantified at present.

frequency during cardiac operations, not only intraoperatively but also in the early postoperative period [3, 4]. The expanding use of TEE in adult cardiac operations has provided a large amount of new information not available previously. This review summarizes and evaluates the current applications of TEE, and in particular, identifies situations where such information may be used to alter patient care and potentially lead to improved outcome. A description of techniques and equipment is beyond the scope of this review and detailed accounts have been presented elsewhere [2]. Utility a n d A d v a n t a g e s of T r a n s e s o p h a g e a l E c h o c a r d i o g r a p h y in R e l a t i o n to Operation The use of echocardiography during cardiac operations is not a new concept. Johnson and co-workers in 1972 [5] first described the use of this technique to evaluate the results of mitral valve operations. During the intervening years there have been many refinements in technology Some centers have used epicardial echocardiography widely in a variety of areas, not only to assess ventricular function, but also the adequacy of valve repair [3, 4] and to delineate patterns of atheroscierotic disease in the ascending aorta [6]). For surgeons the perceived disadvantages to the epicardial approach have been that the probe necessarily transgresses the sterile field, and inevitably leads to an interruption to the operative procedure. The obvious extension of this aspect is that it cannot be used for continuous monitoring [3, 4]. In the postoperative period standard transthoracic imaging can be unsatAddress reprint requests to Dr Kouchoukos,JewishHospitalat Washington University Medical Center, 216 N KingshighwayBlvd, St. Louis, MO 63110. © 1995 by The Society of Thoracic Surgeons

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Ventricular Function The standard techniques used intraoperatively for assessment of ventricular function continue to be electrocardiography and measurement of cardiac output by thermodilution techniques, and other hemodynamic data 0003-4975/95/$9.50 0003-4975(94)00818-R

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derived from pulmonary artery catheterization. The inability of these methods to determine directly end systolic and end diastolic volumes, ventricular filling and contractility, and the presence of valvular dysfunction, all of which can be determined readily by TEE, makes it a potentially attractive and powerful tool for monitoring overall cardiac performance intraoperatively. Transesophageal echocardiography has been widely used for analysis of segmental wall motion abnormalities, particularly in patients with ischemic heart disease [11]. It detects wall motion abnormalities very accurately and may be more sensitive than electrocardiographic monitoring for the detection of ischemia [12]. Biplane imaging for the detection of such wall motion abnormalities is more sensitive than single plane imaging [13]. In addition, several studies using segmental TEE have shown that dysfunctional segments demonstrate improved wall motion after revascularization, which appears to be maintained beyond the immediate postoperative period [13-151. Although the sensitivity of TEE in detecting such changes makes it a powerful research tool whether its routine use during myocardial revascularization procedures is justified or necessary is unresolved [16]. Apart from the subjective assessments of contractility that can be made with TEE, attempts have been made to derive objective hemodynamic data, in particular cardiac output. Earlier attempts to measure cardiac output using transthoracic pulsed Doppler echocardiography showed that stroke volume and cardiac output could be determined accurately noninvasively [17]. There have been a number of recent studies comparing hemodynamic data derived from TEE and conventional thermodilution techniques, although the degree of correlation found has not been consistent [18, 19]. Further advancements in technology are likely to make accurate monitoring of cardiac output by the transesophageal route possible. Hemodynamic monitoring of cardiac function using thermodilution techniques alone can be misleading. Reichert and colleagues [7] performed TEE in 60 consecutive hypotensive patients after cardiac operation. There was agreement between TEE and conventional hemodynamic monitoring as to the cause of hypotension in only 50% of patients. However, TEE identified tamponade in 2 patients and hypovolemia in 6 patients and prevented reoperation in 5 patients. More complex measures of left ventricular function may also be derived from TEE when combined with measurements of intraventricular pressure. O'Kelly and associates [20] have derived indices of left ventricular contractility, end systolic stress, and end systolic area. Other measurements, such as ejection fraction, can be determined by TEE, but because of the calculations required to derive left ventricular volumes, they are not of immediate practical value.

Intracardiac A i r After operations involving cardiotomy or aortotomy most cardiac surgeons follow a protocol for the removal of

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retained intracardiac air. Air can be seen without difficulty by TEE as "microbubbles.'" Orihashi and colleagues [21] have reported another form of air, "'pooled air," which was identified in all patients examined. This was observed primarily in the right superior pulmonary vein, the left atrium, the apex of the left ventricle, and the right coronary sinus of Valsalva. The incidence of retained intracardiac air is much more common after cardiac operations with a cardiotomy (79%) than after coronary artery bypass grafting (11%) [22]. However, a crucial question is whether there is an adverse effect on postoperative neuropsychologic function when intracardiac air, as viewed by TEE is not totally eliminated. Topol and co-workers [23] found no correlation between neurologic outcome and the concentration of microbubbles in a series of 82 patients. They suggested that vigorous maneuvers to attempt to remove all microbubbles may not be necessary. In contrast, Oka and colleagues [22] described the use of a complex series of TEE-guided clearing maneuvers but despite this protocol reported two adverse clinical outcomes in a series of 52 patients, which they attributed to retained air. Further studies using preoperative and postoperative neuropsychologic testing will be necessary to assess the role of retained air, and the influence of TEE-guided removal of air on postoperative neurologic function.

Valve Operations The accuracy of TEE in the assessment of native valve dysfunction and prosthetic valve function has been clearly established [1]. The use of TEE intraoperatively as an aid to surgical decision making in valvular heart disease is increasing. The aortic valve is not often amenable to repair and the majority of operations involve prosthetic valve replacement. However, intraoperative assessment of the aortic valve by TEE may show mild to moderate degrees of leakage that indicate that antegrade cardioplegic administration may be ineffective. Transesophageal echocardiography may be helpful during aortic valve replacement, both for sizing the valve annulus and confirming satisfactory valve function after implantation [24]. Similarly Kouchoukos and colleagues [25] have found intraoperative TEE useful in assessing the feasibility of and confirming satisfactory valve function after operation in relation to pulmonary autograft replacement of the aortic valve. In the presence of endocarditis of the aortic valve, TEE is clearly superior to transthoracic imaging in terms of its morphologic accuracy [26] and has been used intraoperatively to locate abscess cavities (Fig 1). In addition, intracardiac fistulas can be located and their closure or persistence after repair can be confirmed [27]. Because the mitral valve is commonly amenable to surgical repair, the use of intraoperative echocardiography to define accurately the cause of the valve dysfunction (Fig 2), and to assess the immediate results of repair should provide important information. First, what degree of regurgitation at the time of operation, particularly when the valve dysfunction is ischemic in Origin, requires

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Fig 1. View of the aortic root in a patient with bacterial endocarditis. An abscess cavity is clearly visualized (A). Accurate morphologic data may aid both the planning of the required operation and intraoperative localization of abscess cavities.

repair [28]? Second, how does it compare with other methods of assessment of a satisfactory mitral repair [29]? Third, what is the impact of an apparently unsatisfactory result by TEE on operative outcome and the need for reintervention [28, 30-34]? Last, does the use of TEE actually have a positive effect on overall patient survival and functional status [28]? Prebypass imaging by TEE may either dissuade or encourage the surgeon to perform a mitral valve procedure. Sheikh and colleagues [28] reported that a mitral valve procedure was not performed in 11% of patients where one was planned preoperatively using intraoperative TEE. In another study from the same group evaluating a consecutive series of 154 patients undergoing valve operation, some change in the procedure was prompted by TEE in 19% of patients [31]. This is of particular relevance in operations in patients with recent infarction or acute ischemic syndromes, where the degree of mitral regurgitation may vary temporally. In terms of assessing the immediate results of mitral valve repair using TEE and other methods, Moulijn and co-workers [29] compared passive filling of the flaccid left ventricle with TEE, as indices of mitral valve competence intraoperatively, against postoperative left ventricular angiography in 27 patients undergoing mitral repair. They found that TEE was no better a predictor of residual mitral regurgitation after repair than filling of the flaccid left ventricle. However, they acknowledged that filling of the flaccid left ventricle was an entirely subjective measurement. In contrast, Dahm and colleagues [33] demonstrated significant mitral regurgitation requiring further operation by TEE in 3 of 30 patients undergoing mitral repair that was not detected by filling of the flaccid left ventricle. After repair, intraoperative TEE identifies residual mitral regurgitation requiring further surgical intervention, which can occur in up to 16% of patients [28-34]. Transesophageal echocardiography can demonstrate the struc-

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tural defect responsible for the residual regurgitation that appears to be more common in those with anterior leaflet prolapse [32]. In addition, identification of systolic anterior motion after mitral repair and its correction by partial or complete annuloplasty ring removal has been possible with TEE guidance [35]. Jebara and associates [36] have developed the "sliding leaflet technique" to avoid systolic anterior motion in those judged to be at risk, and have documented excellent results supported by TEE monitoring. Sheikh and colleagues [28] found that patients with residual (2+) mitral regurgitation after bypass TEE were at much higher risk of dying (50%) in the early postoperative period. Fix and co-workers [37] found that mild to moderate residual regurgitation (1+ to 2 +) did not confer increased morbidity and mortality, but did increase the risk of late reoperation. These investigators [37] suggest that their low threshold for further operation to correct residual regurgitation may explain the different findings of these two studies. Although the data are not conclusive, the advantages of the use of intraoperative TEE in mitral valve repair suggest that it is equal or superior to other techniques. It not only allows appropriate selection of patients for repair but can confirm the adequacy of repair. Where significant residual regurgitation exists, an aggressive approach to additional operation to correct this appears to be supported by improved patient outcome and reduced risk of reoperation. Transesophageal echocardiography is useful for assessing the tricuspid valve after repair. As with the mitral valve, where there is doubt about the severity of the valvular regurgitation preoperatively, TEE may indicate that repair is unnecessary in up to 10% of those patients in which it had been planned [33, 34]. Similarly, unsatisfactory degrees of regurgitation after repair may prompt further surgical intervention. Techniques have been devised that allow adjustments of the tricuspid annulo-

Fig 2. Mitral valve anatomy off'unction and dysfunction can be visualized clearly. Localized prolapse (P) of the posterior leaflet is demonstrated clearly, allowing successful treatment by quadrangular resection and ring annuloplasty.

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plasty under echocardiographic control after discontinuation of cardiopulmonary bypass. The ends of the annuloplasty sutures are passed through the right atrial free wall [34] and are tied when tricuspid regurgitation is minimal or absent by TEE. This technique may be the ideal method for optimizing the results of tricuspid annuloplasty. The use of TEE as an aid to decision making in the surgical treatment of hypertrophic obstructive cardiomyopathy has been reported by several groups [38, 39]. Marwick and co-workers [38] reported the use of TEE in a series of 50 patients where persistent outflow tract gradients after initial septal myectomy prompted additional myectomy in 10 patients (20°) with satisfactory results in the early postoperative period. Grigg and associates [39] studied a group of 32 patients with hypertrophic obstructive cardiomyopathy who, when compared to a control group, demonstrated a significantly longer length of mitral valve leaflets and abnormal mitral leaflet coaptation. Transesophageal echocardiography confirmed a satisfactory myectomy in all but 1 patient.

Aortic Operations Transesophageal echocardiography as a diagnostic aid in the management of acute aortic dissection represents a major advance, because not only is it rapidly and easily performed at the bedside with minimal morbidity, but it also has a high degree of diagnostic accuracy [40, 41] (Fig 3). It provides precise anatomic data from the proximal ascending aorta, the arch, and the proximal descending thoracic aorta, and also provides information about the presence and degree of aortic insufficiency. Many centers now regard it as the single investigation required before proceeding to operation [42]. Adachi and colleagues [41] recently reported accurate diagnosis in 44 of 45 patients (98%) with acute aortic dissection. Erbel and associates [43] in their study attributed the low rate of in-hospital mortality before operation to rapid investigation by TEE and initiation of treatment. This study also suggested that certain features noted by TEE (ie, fluid extravasation or patent false lumen) implied a higher operative risk. Thrombus in the false lumen was regarded as a good prognostic sign. In some cases where TEE is not diagnostic for acute dissection, computed tomography, magnetic resonance imaging, or aortography may be necessary to maximize diagnostic accuracy [44]. Intraoperatively, TEE can confirm satisfactory aortic valve function when valve resuspension has been performed, and when cardiopulmonary bypass is instituted retrogradely through the femoral artery it can confirm satisfactory flow to the great vessels [45]. Transesophageal echocardiography is also useful for serial studies, in combination with magnetic resonance imaging and computed tomography, to study postoperative changes in the thoracic and abdominal aorta that can occur when residual dissection is present [44, 46]. Transesophageal echocardiography has been used during resection of thoracic aneurysms to monitor myo-

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Fig 3. Transesophageal echocardiography often can visualize clearly an acute dissection in the ascending aorta, allowing the operation to proceed expeditiously.

cardial function. A study by Imagawa and associates [47] using intraoperative transesophageal monitoring found that hemodynamic stability was achieved more effectively with left heart bypass rather than with simple aortic clamping. Another potential use of TEE has been to monitor the degree of left ventricular distention and the need for venting during operations on the descending thoracic and thoracoabdominal aorta during cooling and rewarming for hypothermic circulatory arrest (N Kouchoukos, unpublished observation). Severe atheromatous disease of the ascending aorta can represent a problem in patients who require myocardial revascularization, particularly the elderly [48]. Patients with severe atheromatous disease are at higher risk of stroke and other atheroembolism and several groups [48-51] have developed strategies to reduce this risk by a combination of open removal of protruding atheromas or replacement of the severely diseased ascending aorta and aortic arch. Transesophageal echocardiography appears to be useful in the detection and grading of atheroma in the aortic arch [49, 50]. Philips [52] and Black [53] and their colleagues have demonstrated that TEE may underestimate the severity of the disease when compared to that determined by epiaortic scanning in the mid and distal parts of the ascending aorta. C a r d i o p u l m o n a r y Transplantation There have been few studies reporting the use of TEE in patients undergoing cardiopulmonary transplantation. Transesophageal echocardiography has been reported to be useful in the assessment of donor heart function [54] when standard transthoracic imaging was unsatisfactory. Postoperative follow-up studies of patients after orthotopic transplantation using TEE have demonstrated excellent imaging of intraatrial anatomy and atrioventricular valve function [55, 56] and, in particular, accurate identification of left atrial thrombus and spontaneous atrial echo contrast that was, on occasion, accompanied

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by systemic embolization [55, 56]. The relatively high incidence of these findings suggests that anticoagulant therapy may be indicated in such patients to minimize the potential for embolization [55, 56]. Further studies using intraoperative and serial TEE are needed to examine the effect of modifications in surgical technique on variables such as tricuspid regurgitation and left atrial size and the development of intracardiac thrombus. Transesophageal echocardiography has proved valuable in imaging pulmonary vascular anastomoses after lung transplantation [57]. Satisfactory imaging of pulmonary vascular anastomoses after lung transplantation is usually not possible using transthoracic echo. Satisfactory TEE imaging of all of 14 pulmonary vein anastomoses and 7 right (100%) and 5 of 7 left (71%) pulmonary artery anastomoses was achieved by Hausmann and associates [57]. Thrombosis of one pulmonary venous anastomosis was diagnosed by TEE, and was successfully treated by thrombolysis; two pulmonary arterial anastomotic strictures were diagnosed by TEE and treated surgically.

Pediatric Operations Although intraoperative use of epicardial echocardiography has been pursued by several groups [58, 59], the application of TEE in the pediatric group has been limited by the large size of commercially available probes. With further technologic improvements and increasing experience, the applications for TEE have become more clearly defined in this population [59, 60] and has been thoroughly reviewed recently by others, although this is inevitably a rapidly developing area.

Postoperative Use of Transesophageal Echocardiography Transthoracic imaging in the early postoperative period can be difficult because of the presence of air and chest tubes in the mediastinum and hyperinflation of the lungs that make satisfactory images difficult to obtain [7]. Transesophageal echocardiography has rapidly become the diagnostic modality of choice to supplement basic hemodynamic monitoring postoperatively, particularly when there is an unexplained hemodynamic deterioration [7, 61]. Transesophageal echocardiography can prompt surgical reintervention in 10% to 66% of patients [7, 61]. This broad range can be explained by the variability between different surgical units in their application of mechanical circulatory support to postoperative patients with univentricular or biventricular failure. Transesophageal echocardiography can identify correctly atypical tamponade [62], and it may spare patients a thoracotomy when hemodynamic data suggests tamponade, but no evidence for tamponade is observed by TEE [7, 61]. Transesophageal echocardiography can also complement hemodynamic data for the assessment of hypovolemia or ventricular failure as a cause of hypotension and prompt appropriate intervention. The mortality of cardiac surgical patients who undergo TEE is high,

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around 50%, by virtue of the condition of the patients at the time of study [7]. Transesophageal echocardiography is also useful in serial monitoring of patients requiring mechanical circulatory support [63, 64]. In this situation it can visualize pericardial clot and the presence of intracardiac shunts. In addition, serial TEE studies assessing recovery of ventricular function can be used to predict successfully weaning from ventricular assist devices [63, 64]. Transesophageal echocardiography can be used to monitor accurately positioning of intraaortic balloon pumps in the thoracic aorta, particularly when antegrade placement is necessary because of atheroma in the descending aorta [65, 66]. Similarly, the ability of TEE to image intracardiac cannulas accurately has also led to its use to assist the positioning of atrial cannulas at the time of insertion of ventricular assist devices [67].

Conclusion The development of TEE as a diagnostic tool and its application to cardiovascular surgical patients has occurred rapidly. With increasing experience it is likely that additional areas of usefulness will be identified. It is important to differentiate between the information derived from TEE that has a definite influence on surgical decision making and the potential for improved patient outcome, from that where the derived data, although novel and interesting, does not actually influence decision making or outcome. In this review we have tried to draw this distinction and to highlight areas where further information is needed to assess the value of TEE in a particular area. It is clear that to practice effectively now and in the future and to offer optimal care to their patients, cardiac surgeons and anesthesiologists will require substantial training and expertise in the principles and practice of TEE.

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