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Ann Thorac Surg 2001;72:S2214-S2218
© 2001 The Society of Thoracic Surgeons
a VA Boston Healthcare System, Harvard Medical School, Boston, Massachusetts, USA
* Address reprint requests to Dr Al-Tabbaa, Department of Surgery (112), VA Boston Healthcare System, 1400 VFW Parkway, West Roxbury, MA 02132, USA
e-mail: amer.al-tabbaa{at}med.va.gov
Presented at Monitoring and Improving Patient Safety During and Following Cardiac Surgery, San Diego, CA, May 5, 2001.
Abstract
Use of intraoperative echocardiography during open heart surgery, transesophageal probes, high-frequency transducers, and color Doppler imaging provide important diagnostic information to surgeons and anesthesiologists. Early detection of myocardial ischemia, assessment of valvular disorders, and the ability to monitor for intracardiac air are among the most important roles of intraoperative transesophageal echocardiography. Large prospective studies are necessary to evaluate whether these changes affect the outcome of patients undergoing coronary artery bypass grafting in terms of morbidity, mortality, hospital length of stay, and functional recovery. The application of new techniques such as contrast-enhanced transesophageal echocardiography helps to assess the adequacy of cardioplegia distribution and, thus, myocardial protection during cardiopulmonary bypass, which has a significant influence on outcomes as well.
The use of intraoperative echocardiography during open-heart surgery dates to the 1970s, when epicardial echocardiography first became available. However, it was not until the mid-1980s, with the development of transesophageal probes, high-frequency transducers, and color Doppler imaging, that this technique was able to provide important diagnostic information to surgeons and anesthesiologists. The early detection of myocardial ischemia, assessment of valvular disorders, and the ability to monitor for intracardiac air are among the most important roles of intraoperative transesophageal echocardiography (TEE). At our hospital, intraoperative TEE is performed on virtually all patients undergoing open heart surgery; other centers rely on TEE only for high-risk patients or valve surgery.
Safety
Intraoperative TEE has proved to be safe. The incidence of serious complications is less than 3% and the reported mortality rate associated with TEE is 0.01% to 0.03% [1]. There have been isolated case reports of dental injury, pharyngeal and laryngeal trauma, esophageal bleeding and perforation, respiratory distress, hemodynamic instability, arrhythmias, and transient bacteremia [1–3]. The respiratory and cardiovascular side effects are more likely in very small children when a probe of an appropriate size is not available. Vocal cord trauma has been reported in patients undergoing craniotomy in the sitting position. Esophageal and gastric complications are rare, although they can be lethal [2]. Urbanowicz and colleagues [4] demonstrated that an esophageal ultrasound probe, even when maximally flexed, almost never exerted a pressure on the esophageal mucosa enough to compromise capillary perfusion. Nevertheless, as evidenced in their and other reports, in patients with upper gastrointestinal tract and intrathoracic comorbidities severe injury can occur that is apparently ischemic in origin [2, 4]. Therefore TEE is often contraindicated in patients with a history of esophageal pathology or surgery [2].
Standardization
With the increase in use of TEE in the operating room, there has arisen a need for standardization of the terms and the technique used, to make observations and reports comparable and useful for clinical and research purposes. In 1996 the American Society of Anesthesiologists and the Society of Cardiovascular Anesthesiologists Task Force on Transesophageal Echocardiography [1] published the "Practice Guidelines for Perioperative Transesophageal Echocardiography." In this paper, the various indications for the use of intraoperative TEE were analyzed and classified into three different categories according to the strength of the data available in its support. Category I includes the strongest evidence support or expert support and the most likely to affect outcomes. Category III includes the weakest indications for TEE. In 1999 the Task Force [5] published the "ASE/SCA Guidelines For Performing a Comprehensive Intraoperative Multiplane Transesophageal Echocardiography Examination," with the objective of facilitating training, enhancing quality improvement, and facilitating communication between centers . They described the technique to obtain the 20 standard echocardiographic views that comprise a complete examination of the heart.
Validation
The interpretation of TEE images is subjective and highly dependent on the level of training of the ultrasonographer. There have been concerns about the accuracy of the readings done by the anesthesiologist in real time compared with the interpretation off-line of the same images in the echocardiography laboratory [6, 7]. Bergquist and colleagues [7] reported a moderate correlation of real-time estimates of left ventricular ejection fraction area with off-line quantification. Correlation was much higher when only recognition of normal and severe RWMA were compared.
Transesophageal echocardiography has been compared to other techniques in its ability to detect ischemia and to assess ventricular function. Multiple reviews have compared TEE with electrocardiography (ECG) and use of pulmonary artery catheters for detection of ischemia [8–12]. Konstadt and colleagues [10] determined that TEE can accurately assess left ventricular filling and ejection when compared with epicardial echocardiography. The literature consistently reports that regional wall motion abnormalities (RWMA) precede ST changes and increase in left ventricular filling pressures in the presence of ischemia [9, 11, 12].
Assessment of myocardial injury during and following cardiac surgery
Left ventricular systolic function
Tennant and Wiggers [13] described the relationship between myocardial perfusion and regional wall motion in 1935 using an open-chest animal model. Since then, several investigators have demonstrated that RWMA follow the onset of ischemia in 10 to 15 seconds. We also know the pathophysiologic mechanisms that lead to these RWMA. These include hypoxia, regional acidosis, and impairment of the delivery of calcium to the contractile elements of the myocardial cell [8]. The incidence of perioperative acute myocardial infarction in patients undergoing coronary artery bypass grafting (CABG) has been reported to be as high as 21% [14]. It makes sense then that real-time monitoring of myocardial contractility will prove to be a sensitive means to detect ischemia and could direct the pharmacologic or surgical approach to its treatment. Intraoperative echocardiography allows this level of monitoring.
The ability to evaluate the left ventricular function with TEE was one of the factors that favored the use of the technique in the operating room. Early reports validate the accuracy of TEE for this purpose as mentioned above [6, 7]. However, most of these studies were performed using older technology (monoplane TEE), which fails to interrogate the left ventricle (LV) as a three-dimensional structure. Modern technology allows extensive qualitative and quantitative analysis of the LV. Several approaches have been used to quantify left ventricular systolic performance. M-mode echocardiography, Doppler, and two-dimensional echocardiography have all been used to develop formulas that can calculate linear (fractional shortening), two-dimensional (fractional area change), and three-dimensional (ejection fraction) indices of LV systolic function [15, 16]. The ejection fraction (EF) continues to be the most widely used index of LV systolic function. All systolic indices are dependent on preload and afterload. A pitfall of calculating EF as opposed to linear and two-dimensional indexes is that the degree of error can be magnified because of the three-dimensional nature [15]. Some authors have reported that subjective qualitative estimates of EF are as precise as, or even superior to, quantitative measurements [17, 18]. By using the modern multiplane echo probes, the examiner can integrate several windows of interrogation of the LV when estimating global LV function. This approach is quick, is reproducible among experienced echocardiographers, and may in fact reflect more accurately the architecture of the LV.
Multiplane TEE allows examination of the LV from different echocardiographic windows. This permits accurate description of the location and extent of RWMA. Patients undergoing CABG were assigned to Category II when undergoing monitoring for ischemia. The use of TEE to evaluate myocardial perfusion, coronary artery anatomy, or graft patency were considered to be Category III indications [1]. The Subcommittee on Quantification of the American Society of Echocardiography (ASE) recommends the use of a 16-segment model that consists of six segments at the basal level, six segments at the midpapillary level, and four segments at the apical level. The echocardiographer can correlate each segment with the coronary artery that most frequently provides its blood supply. The recommended qualitative grading scale for wall motion is as follows: 1 = normal (>30% thickening), 2 = mild hypokinesis (10% to 30% thickening), 3 = severe hypokinesis (<10% thickening), 4 = akinesis (no thickening), and 5 = dyskinesis (paradoxical movement during systole) [5].
As mentioned above, impairment in coronary perfusion triggers the ischemic metabolic cascades that very rapidly result in wall motion abnormalities in the segments involved. We have presented evidence in this review that TEE is a sensitive means of detecting perioperative ischemia in real-time by detection of new RWMA (76%) [7]. Several authors [7, 9] define a new RWMA as an increase by two or more points for at least one segment for more than 1 minute. Some of the studies addressing the accuracy of online detection of ischemia were done with older technology (eg, biplane TEE probes); therefore we suspect that the sensitivity of multiplane TEE for detecting new ischemic episodes might be higher. Including mild RWMA (hypokinesis) as a criterion for the diagnosis of ischemia increases the sensitivity but decreases the specificity of TEE [11]. It is important to recognize that not every RWMA represents ischemia. Loading conditions, conduction abnormalities, ventricular pacing, and myocarditis are nonischemic causes for RWMA [9]. Regional variation also exists. The basal segment of the interventricular septum (membranous septum) is usually hypokinetic compared with its midpapillary and apical segments.
Left ventricular diastolic function
Evaluating LV diastolic performance is complicated and of limited utility in the intraoperative setting. Virtually every echocardiographic technology has been used in an attempt to measure LV diastolic function. Currently, Doppler spectral analysis of the transmitral and pulmonary venous flows is used to assess LV diastolic function [15]. However, for two different measurements of LV diastolic function to be comparable, similar preload and afterload conditions must exist. Therefore, at this time, intraoperative assessment of diastolic function is impractical.
Hemodynamics/volume status
Intraoperative TEE has been used extensively to monitor for hemodynamic changes, and can complement the use of invasive hemodynamic monitors such as pulmonary artery catheters (PAC). In the laboratory, calculation of hemodynamic variables that are usually measured by other means (eg, pulmonary artery catheters) has been achieved [1]. In addition, TEE enhances the diagnosis of hemodynamic disturbances and often time directs the clinician in the implementation of appropriate corrective measures [1, 19]. When evaluating the influence of TEE on intraoperative decision making, Bergquist and colleagues [19] reported that TEE was the single most important guiding monitor in 17% of instances. When considering all of the various interventions, fluid administration was influenced the most (30%) by TEE, followed by PAC (7%). Because preload is physiologically determined by sarcomere length, a variable that is more accurately estimated by volume than by pressure measurements, it would make sense that TEE and PAC data would complement each other [1].
The ASA/SCA task force classifies an increased risk of hemodynamic complications during the perioperative period as a Category II indication for perioperative TEE. The risk of perioperative hemodynamic complications is determined by conditions related to the patient, procedure, and clinical setting. Emergent use of perioperative TEE to determine the cause of acute, persistent, life-threatening hemodynamic disturbances in which ventricular function and its determinants are uncertain and have not responded to treatment is a Category I indication [1].
Mitral regurgitation
When evaluating for ischemia after cardiopulmonary bypass (CPB) it is important to interrogate the mitral valve. Balu and colleagues [20] report that 60 of 1,530 patients (4%) diagnosed with coronary artery disease (CAD) by angiography had mitral regurgitation that could not be assigned to any structural abnormality, leaving ischemic heart disease as the possible cause. Mitral regurgitation in CAD can occur acutely during a myocardial infarction or can develop chronically due to ischemia-induced papillary muscle dysfunction. Inferior and posterior RWMA are associated with mitral regurgitation. This can be explained by the blood supply to the posteromedial papillary muscle, which is provided by branches of either the right coronary artery or the left circumflex as opposed to the anterolateral papillary muscle, which receives a dual blood supply [21, 22].
Assessment of viability
Intraoperative echocardiography as a field is expanding. Several groups of investigators are making efforts to develop and to incorporate new techniques and technology into the routine examination. It is worth mentioning some of those techniques here. Sonicated echo–contrast injections have been used to enhance the detection of new RWMA and to evaluate the distribution of cardioplegia (myocardial perfusion) during CABG [23, 24]. Aronson and colleagues [25] reported on the use of intraoperative, low-dose dobutamine echocardiography to assess myocardial viability before surgery and to evaluate the adequacy of myocardial revascularization. Dobutamine stress echocardiography is a good technique to differentiate between hibernating (chronic ischemia), stunned (acute ischemia-reperfusion), and nonviable myocardium (infarcted). This differentiation appears to be important in planning the medical or surgical interventions that will best suit a particular patient. It may also be a significant prognostic factor both before and after revascularization. Color kinesis technology based on automated border detection appears to be promising in aiding the detection of RWMA and evaluation of global LV systolic function [9, 16]. However, it is still in its development stage and is highly dependent on operator skill. The availability of digital imaging and side-by-side comparison of recorded base line versus real-time images using cine-loop technology may enhance the accuracy of online detection of new RWMA [7, 26].
Prognostic value and impact on decision making and outcomes of intraoperative TEE during CABG
Bergquist and colleagues [19] studied the influence of TEE on intraoperative decision making as compared with use of ECG, arterial and pulmonary artery catheters in 75 patients undergoing CABG. They found that TEE was the single most important guiding factor in 17% of the 584 interventions recorded. The majority of the interventions influenced by TEE involved fluid administration or antiischemic therapy. An additional 43% of interventions were based on supportive data from TEE monitoring. Other therapies guided by TEE included vasopressor or inotrope administration, and vasodilator therapy. Critical events that were influenced by TEE occurred in 2 of 75 patients (3%). One patient required emergent return to CPB to repair a graft that kinked upon chest closure; the second patient required the addition of retrograde cardioplegia when a previously unrecognized aortic insufficiency was diagnosed.
Leung and colleagues [12] compared the significance of new RWMA against other monitors (ECG, systemic blood pressure, and pulmonary artery pressure) by using continuous TEE, Holter monitoring and hemodynamic measures before and after bypass and early postoperatively in the intensive care unit (ICU). The prevalence of ischemia when detected by TEE was higher consistently throughout the three periods. Neither prebypass TEE ischemia nor ECG ischemia in any of the three periods was predictive of poor outcome. In contrast postbypass TEE ischemia was predictive of outcome: 6 of 18 patients with postbypass TEE ischemia had adverse outcomes (two cardiac deaths, three myocardial infarctions, and one ventricular failure) compared with none of 32 patients without postbypass TEE ischemia.
Click and colleagues [27] published a review of all adult patients who had cardiac surgery with intraoperative TEE between 1993 and 1997 at the Mayo Clinic. New findings before and after CPB and alterations in the planned surgical procedure or management were documented prospectively. There were a total of 480 new pre-CPB findings in the 3,245 cases reviewed (15%). Newly discovered patent foramen ovale (PFO) accounted for 100 of the new pre-CPB findings. In 88 of those patients the surgeon elected to close the PFO in addition to the originally planned surgical procedure. In 96 patients intraoperative TEE assessment of the mitral valve found no significant structural or functional abnormality. The surgeon elected not to inspect the mitral valve in 95 of those patients, based on the intraoperative TEE. Overall, pre-CPB TEE had a significant impact in the surgical management of 14% of the patients. Post-CPB TEE produced new findings in 180 cases (6%). The most frequent was inadequate native valve repair; in 32 of these 53 patients the repair was revised or the valve was replaced immediately. When all types of procedures performed were considered, 2% of the patients were returned to CPB for corrections based on TEE. During the period of the study, only 9% of the patients undergoing CABG had intraoperative TEE; however, new post-CPB findings were reported in 8% of the patients in this group.
Mishra and colleagues [28] presented evidence of the usefulness of intraoperative TEE in formulating the surgical plan, guiding various hemodynamic interventions, and assessing the immediate results of surgery. They studied 5,016 adult patients who underwent cardiac surgery, 3,660 cases of CABG, and 1,356 cases involving valves, between 1993 and 1997 at the Escorts Heart Institute and Research Center in New Delhi. Pre-CPB TEE yielded new findings that either helped or modified the surgical plan in 27% and 12% of the cases respectively. The TEE-guided hemodynamic interventions occurred in 26% of the CABG and 10.47% of the valve procedures. Post-CPB TEE identified the need for graft revision in 0.8% of cases, intraaortic balloon pump in 0.8%, and revision of valve repair in 2.08%. For the entire series, 39% of the patients benefited from pre-CPB and 40% from post-CPB use of TEE.
Kato and colleagues [29] studied a series of 50 patients to determine the impact of TEE on the postoperative outcome in patients undergoing CABG. They found that post-CPB RWMA guided additional medical or surgical therapy, resulting in resolution of RWMA by the end of surgery in 11 of 15 patients (73%). These data include 4 patients with postoperative MI and 2 who died from cardiogenic shock.
Conclusion
Review of the literature confirms that intraoperative TEE is a safe and reliable technique when performed by trained clinicians. Several reports attest to the advantages of TEE over other monitors in detecting previously unrecognized anatomical abnormalities, new-onset RWMA, and complex hemodynamic disturbances. It is not surprising, therefore, that TEE appears to be the single most important monitoring technique in guiding the intraoperative formulation of medical and surgical therapy.
Large prospective studies are necessary to evaluate whether these changes affect the outcomes of patients undergoing CABG in terms of morbidity, mortality, hospital length of stay, and functional recovery. In the meantime, it appears that confirmation of successful revascularization and sparing patients from reoperation by correcting defective grafts and incomplete valvular repair before they leave the operating room has a positive effect.
Detecting the subset of open heart surgery patients who are most vulnerable to adverse outcomes remains a challenge to echocardiographers. It seems clear that the appearance of new RWMA after CPB strongly identifies patients at high risk. The application of new techniques such as contrast-enhanced TEE helps in assessing the adequacy of the distribution of cardioplegia and thus myocardial protection during CPB. This appears to have a significant influence on outcome as well.
Despite the limitations of TEE in the intraoperative setting, and the need for ongoing research and development, this technology remains a safe and reliable source of important information for the surgical team aiming to provide state-of-the-art care.
References
This article has been cited by other articles:
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  S. Matsushita, Y. Sakakibara, T. Imazuru, M. Noma, Y. Hiramatsu, O. Shigeta, T. Jikuya, and T. Mitsui High-frequency QRS potentials as a marker of myocardial dysfunction after cardiac surgery Ann. Thorac. Surg., April 1, 2004; 77(4): 1293 - 1297. [Abstract] [Full Text] [PDF]
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