Transesophageal Echocardiography in Noncardiac Thoracic Surgery




Transesophageal Echocardiography in Noncardiac Thoracic Surgery



Breandan Sullivan, Eric Leiendecker



Abstract


Patients undergoing noncardiac thoracic surgery have become increasingly complex over time. Managing the hemodynamics of these patients is made easier and safer with appropriate, real-time information about cardiopulmonary function. There has been expansion of the role of transesophageal echocardiography (TEE) from cardiac surgery applications to the management of thoracic surgery patients, expansion limited largely by a lack of trained providers. TEE use is relatively safe, with most complications being minor and related to the insertion of the TEE probe, major complications can be reduced by proper patient screening and adherence to suggested indications. The benefit of using TEE is the providing of real-time, actionable, information that can influence the hemodynamic management of this increasingly complex patient population. Compared with traditional monitoring techniques, TEE is the only monitor that can provide a comprehensive assessment of biventricular and valvular function in addition to evaluation of the great vessels and estimation of pulmonary artery pressures—all of which can change rapidly in the course of thoracic surgery. In addition, there has grown a specific role in the performance of lung transplantation where TEE is used to evaluate the arterial and venous anastomosis and provide information regarding the patency of these to the surgical team. The use of TEE has been expanding in recent years to assist in the management of thoracic surgery patients and has been found to be not only be useful in this population, but also safe.


Keywords


TEE; echocardiography; thoracic surgery; lung ultrasound; lung transplant; intraoperative monitoring



Introduction


The use of transesophageal echocardiography (TEE), performed by the anesthesiologist, has become commonplace in cardiac surgery operating rooms in recent years. This has been especially prominent as the use of Swan-Ganz catheters has diminished at the same time. Outside of the cardiac surgery operating room the use of TEE has, thus far, largely been reserved for cases of unexplained hypotension/hypoxia/instability or so-called “rescue TEE.” However, this is changing, and more providers are electing to use TEE for hemodynamic monitoring in general surgery cases. The use of TEE in the thoracic surgery room is a natural evolution of its use in the cardiac surgery operating room because of TEE trained cardiac anesthesiologists often times providing the anesthetic for thoracic surgery patients, and the obvious interplay between the pulmonary and cardiovascular systems. In addition, as the surgical cases grow more complex and challenging, or rely on advanced therapies, such as extracorporeal membrane oxygenation (ECMO), there is an avenue to expand the use of TEE in this arena.


Thus far there is no consensus on indications for the use of TEE in thoracic surgery, save for the “rescue TEE,” like there is for its use in cardiac surgery. However, practice patterns are evolving in a way that make TEE a powerful tool for guiding management of this challenging patient population.



Indications for Transesophageal Echocardiography Use


The accepted guidelines by the Society of Cardiovascular Anesthesiologists published jointly with the American Society of Echocardiographers (ASE) state that the use of TEE in noncardiac surgery is indicated for patients who have known or suspected cardiovascular pathology that may impact the outcome of the surgery. The American Society of Anesthesiologists (ASA) expands on this to state that TEE may be indicated when the patient’s cardiovascular pathology may result in severe hemodynamic, pulmonary, or neurologic compromise.1 In addition, the ASA indicates that the use of TEE is warranted in cases of unexplained life-threatening hemodynamic compromise refractory to corrective measures.2 In cardiac surgery, the indications for TEE remain broad to include all patients undergoing open heart and in particular valvular surgeries and thoracic aortic procedures, while being indicated for select coronary artery bypass grafting (CABG) procedures. With the advent of transcatheter-based intracardiac procedures, the role of TEE has expanded to include procedural guidance during these procedures.


Beyond these, more indications for perioperative TEE are being pursued. There is growing use of TEE in the field of liver transplantation and the American Association for the Study of Liver Disease has issued a recommendation that TEE be used during orthotopic liver transplantation (OLT) to assess for the following: intracardiac chamber sizes, ventricular hypertrophy, systolic function, diastolic function, valvular function, and left ventricle (LV) outflow tract obstruction.3 Wax et al. conducted a survey of anesthesiologists at centers performing more than 40 OLTs per year and found TEE use at least occasionally in 86% of cases and 13% of respondents use TEE for every case.4 Furthermore, TEE findings during various phases of transplantation have been shown to be predictive of major adverse cardiac events (MACE) following surgery. For instance, the finding of intraoperative biventricular dysfunction was shown to be three times more likely than controls to suffer MACE and those with intracardiac thromboemboli were nearly five times more likely to suffer a cardiac event.5 Most institutions that perform liver transplantation require the providers to be ­certified in basic TEE certification.


TEE is also used for monitoring purposes in some urologic surgeries. Recently, a published randomized controlled trial (RCT) compared TEE use during radical cystectomy to current standard of care. In that study, the authors randomized 80 patients and found that the cohort who had TEE-based monitoring received fewer central lines, had shorter durations of mechanical ventilation with fewer pulmonary complications, and showed a lower rate of cardiac arrhythmias.6 Of course, as is the pattern nationally, one limitation of this study is that only cardiac anesthesiologists with training in advanced perioperative TEE, rather than basic, were included as the primary anesthesiologists and these results may be because of anesthesiologists selection as opposed to TEE use per se. Regardless, this highlights the search for novel uses and recognition of the value of TEE as a monitoring tool. In other urologic surgeries, such as resection of renal cell carcinoma with tumor thrombus of the inferior vena cava, TEE is used to evaluate for tumor location and extension, need for cardiopulmonary bypass, and also as a monitor for tumor embolization during the procedure.7


In the emergency setting, point-of-care cardiac ultrasound (US) has been widely adopted in the setting of peri- and intracardiac arrest. Systematic reviews and meta-analysis have shown US to have a high level of accuracy for identifying reversible causes and an upwards of 95% accuracy for predicting short-term survival.8 Alternatively, the absence of cardiac activity on US is also highly predictive of the failure to achieve return of spontaneous circulation.9 In the operating room, the so-called “rescue TEE” has been a well-established tool to evaluate refractory hemodynamic instability. This is likely caused by the high accuracy of the images obtained despite ongoing resuscitation. Diagnoses such as pericardial tamponade, pulmonary embolism (PE), aortic dissection, biventricular dysfunction, and volume status are all accurately assessed using TEE.10 It is no surprise then that TEE during intraoperative cardiac arrests carries with it a similar benefit. This is largely because of the benefits stated previously regarding accuracy of imaging despite ongoing resuscitation.11 Of specific benefit to TEE over transthoracic echocardiography (TTE) is that accurate image acquisition is not impeded by ongoing cardiopulmonary resuscitation and requires no interruption of chest compressions.


Despite these multiple indications, some backed up with clear evidence, there exist no randomized trials of TEE as a monitor for noncardiac thoracic surgery. Regardless, it appears that TEE can be a powerful tool in aiding both the anesthesiologist and the surgeon in managing complex patients.



Transesophageal Echocardiography asa Monitor


The ASA first directly addressed the topic of “vigilance” in a 1992 panel at the annual meeting, and this concept has evolved to make up a large portion of how the specialty is viewed.12 This idea of vigilance in monitoring our patients in the operating room has driven countless technologic advancements seeking to allow physicians to better monitor, interpret, and respond to physiologic changes encountered (and ideally predicted) in the course of surgery. Classically, the pulmonary artery catheter (PAC) has represented the monitor of choice, though there has been growing interest in noninvasive cardiac output monitors, arterial waveform analysis, and TEE. At this time, however, the PAC remains the hemodynamic monitor most commonly used beyond the standard ASA required monitors. This use seems to persist despite lack of evidence for benefit of their use, and in at least one study potential for harm.


The goal of hemodynamic monitoring is to integrate information provided about patient variables into a plan of action that improves the outcome of the patient. In the case of PACs there has yet to be compelling evidence that supports their use in regards to improved outcomes. The Evaluation of Heart Failure and Pulmonary Artery Catheterization Effectiveness Trial (ESCAPE), published in 2005 randomized patients with heart failure to either receive a PAC to guide management or management based on clinical assessment. This study showed that patients receiving PACs were no more likely to be alive at 6 months, or did they have shorter hospitalizations.13 This finding is congruent with multiple reports from the critical care literature showing no apparent benefit to using PACs in patient management. These studies are in agreement with the 2003 publication evaluating the use of PACs in high-risk elderly patients undergoing noncardiac surgery which showed no improvement in 6-month mortality, and showed an increased rate of PE in the treatment group. Subgroup analysis of the sampled group even showed a possible increase in mortality in the group undergoing thoracic surgery, which should lend even more scrutiny to the use of PACs in thoracic surgery.14


In light of this evidence showing that pulmonary artery (PA) catheters are not beneficial in managing heart failure and high-risk patients, then a natural question is “Of what benefit would echocardiography be?” This is an especially pointed question considering the large variability seen in the literature comparing PACs and TEE in one simple monitoring modality: measuring cardiac output. Su et al.15 in 2002 did a direct comparison of esophageal Doppler and PACs in patients undergoing CABG surgery and found an excellent linear correlation between cardiac output values obtained with a PAC and that with TEE. There are retrospective studies comparing the two which showed lower levels of correlation though these have their limitations sufficient to say that with qualified users TEE can get similar values as that of PACs. More recently, there has been an emphasis on noninvasive cardiac output monitors, which appear promising. At least one group compared one device (LIDCO) to TEE and PAC during the prebypass phase of surgical aortic valve replacement for aortic stenosis and found a high degree of reliability in the device for trending cardiac output.16 There are many more groups currently evaluating these devices and how they respond under various physiologic conditions during different phases of cardiac surgery.


Despite the results however, there is information that TEE provides the physician that a PAC or noninvasive cardiac output monitors would not provide. TEE is the only monitor that can provide instantaneous feedback about valve pathology or ventricular function. While the other monitors can provide the cardiac output, TEE has the ability to show the physician how that cardiac output is generated and if there are wall motion abnormalities or diastolic dysfunction. TEE is crucial in evaluating for pericardial disease and effusion, which goes undetected on PACs and other monitors. In addition, in the case of lung transplant TEE can provide information on the pulmonary venous anastomosis, and also indicate the function of the right ventricle (RV). In thoracic aortic surgery, TEE will evaluate for dissection and aneurysm which will of course go unnoticed on other monitors.


Clearly, there are other monitors that may provide useful information. However, the effect of these monitors (PACs) are dubious at best while some provide only very limited information (noninvasive cardiac output monitors). TEE, however, despite no RCT to validate its effect on patient outcomes, provides robust information that can help guide not only patient management by the anesthesiologist, but also surgical planning and execution with a low level of risk.



Risks of Transesophageal Echocardiography


Certainly the use of TEE carries great potential benefit, although we would be remiss if we did not speak about the potential harm of TEE use. The vast majority of the inherent risk of TEE use is related to the insertion of the echocardiogram probe into the oropharynx, around the base of the tongue, and subsequently into the esophagus. The complication that is most worrisome is direct damage to the esophagus. There are multiple reports of esophageal perforation associated with the insertion of the TEE probe. Reportedly, these most feared complications happen in 0.03% to 0.09% in large case series. The majority of these injuries (54.3%) occur in the thoracic esophagus with smaller proportions occurring in the pharyngeal or cervical regions (11.8% and 20.6%, respectively). The majority of these patients in one case series underwent repair of the perforation, though with a significant mortality of (28%) as the direct result of their injuries.17


Although damage to the esophagus is very worrisome, this remains a safe procedure, especially so when the patient is anesthetized in the intraoperative setting. One large case series of intraoperative TEE was done in 2001 and included over 7000 patients. These authors showed an incidence of esophageal injury of 0.01% and of upper gastrointestinal bleeding of 0.03%. In addition, they showed a low mortality rate associated with TEE of 0%. From this case series, we also see that the more common complications that arise tend to be relatively minor with odynophagia occurring in 0.1% of cases and dental injuries occurring in 0.03%.18 More recently in 2007, Piercy et al. evaluated roughly 10,000 cardiac surgical patients and found similar rates of major complications with an incidence of about 1/1000.19


In light of these potential complications, which are nonzero risks, it is important to discuss safety surrounding the use of TEE and ways to avoid these potentially devastating complications. First, as with any procedure in medicine, safety begins with the physician performing a detailed history and physical exam. Largely, this interview and exam will focus on elucidating potential gastrointestinal pathology that would prevent a barrier to passing the TEE probe. A history of esophageal or stomach surgery, or a history of difficulty swallowing should raise the physician’s suspicion of possible complications. If an interview elicits evidence of significant, noninvestigated, dysphagia then a barium swallow test remains the gold standard method of investigation to confirm or refute the presence of esophageal strictures or diverticula which otherwise might result in complications.20 In addition, some attention must be given to questioning the benefit of placing the TEE probe. As discussed earlier, this can be a powerful tool that can lead in certain conditions to a change in surgical planning. However, the possibility of this must be weighed against the potential chance of causing a complication.


Safe handling of the TEE probe is a must. Once the proper screening is done, safe handling by the physician is the last line of defense in preventing a complication. Once the patient is adequately anesthetized, important as the passage of the TEE can be a strong stimulus, intubation of the esophagus can occur under direct visualization or blindly. Under direct visualization, the jaw may be thrust and tongue pulled out to expose the oropharynx through which the probe may be guided, or if done blindly one hand may insert the probe while the other guides it along the back of the tongue and into the esophagus. Occasionally, there is difficulty in passing the TEE probe necessitating direct laryngoscopy to expose the esophagus through which the probe may be inserted. In small patients or those with dysphagia, one consideration would be the use of a pediatric TEE probe, as this has a smaller bore and theoretically is less likely to cause trauma. The probe should be lubricated to reduce friction and an inserted probe should always be unlocked and in a neutral position when inserted or removed (Fig. 55.1).


image
• Fig. 55.1 Comparison of adult and pediatric transesophageal echocardiography probes with ruler for reference. 3D, Three-dimensional; TEE, transesophageal echocardiography. (From Hui L, Sahn DJ. Instrumentation for transesophageal echocardiography. In: Wong P, Miller-Hance W (eds). Transesophageal Echocardiography for Congenital Heart Disease. Springer: London; 2014:Fig. 2.11.)


Intraoperative Hemodynamic Exam


TEE is the only monitor that can provide real-time, immediate assessment of biventricular function, valve function, volume status, wall motion, or presence of effusion. To obtain all requisite information, the standard 28 views should be the minimum exam performed.1 Although these guidelines recommend views obtained, they do not indicate timing of the examination or how often it should be repeated. In addition, there is no current recommendation for how TEE should be used for ongoing monitoring following the completion of the initial exam. It seems reasonable to continue to monitor ventricular function looking for alterations in wall motion, global function, and filling (Table 55.1).



Table 55.1










































Intraoperative Hemodynamic Assessment can Place Patients Into Specific Profiles, the Management of Which Will Differ
Hemodynamic Assessment Left Ventricular Contractility Filling (Left Ventricular End-Diastolic Volume) Diastolic Function Right Ventricular Contractility
Normal Normal Normal Normal Normal
Left ventricular failure Decreased Increased Normal or decreased Normal
Vasoplegia Increased or normal Normal or decreased Normal Normal
Hypovolemia Normal or increased Decreased Normal Normal
Right ventricular failure Normal Decreased Normal Decreased


Image


Following the exam, the probe may be left in the midesophageal four-chamber (ME-4C) position as a monitor. This will provide real-time evaluation of biventricular function, which may change dramatically during periods of thoracic surgery. One-lung ventilation or selective clamping of the pulmonary artery (PA) may severely increase the afterload on the RV, causing dysfunction. Clamping of the atrial cuff to perform anastomoses may result in coronary occlusion and regional wall motion abnormalities. All of these complications can be readily observed on TEE of basic examination images (Fig. 55.2).


image
• Fig. 55.2 Cross-sectional images of the suggested 16 views (approximate angle is indicated top right) of the transesophageal echocardiography. AMVL, anterior mitral valve leaflet; Ao, aorta; AV, aortic valve; IAS, intra-atrial septum; IVC, inferior vena cava; L, left coronary cusp; LA, left atrium; LAX, long axis; LPA, left pulmonary artery; LV, left ventricle; ME, mid-esophageal; MPA, main pulmonary artery; MV, mitral valve; N, non-coronary cusp; PM & AL, posteromedial and anterolateral papillary muscles; PMVL, posterior mitral valve leaflet; R, right coronary cusp; RA, right atrium; RPA, right pulmonary artery; RV, right ventricle; SAX, short axis; SVC, superior vena cava; TG, transgastric; TV, tricuspid valve. (From Fayad A, et al: Perioperative transesophageal echocardiography for non-cardiac surgery. Can J Anaesth. 2018 April; 65(4): 381–398.)


Transesophageal Echocardiography Assessment of the Right Ventricle


In his 1821 work “A Treatise on Diseases of the Chest” RT Laennec pontificates that “All diseases which give rise to severe and long-continued dyspnœa produced, almost necessarily, hypertrophia or dilatation of the heart, through the constant efforts the organ is called on to perform, to propel the blood into the lungs against the resistance opposed to it by the cause of the dyspnœa.”21 Suffice to say that this physiology certainly has not changed in the nearly 200 years following his publication. Luckily, we have learned more about this physiology and the effect it has on the patient and their life. It is relatively common knowledge that pulmonary hypertension (PH) can accompany and mirror the development of severe pulmonary disease. In one series of patients undergoing workup for lung transplantation, 49% were found on right heart catheterization to have mean pulmonary artery pressure (MPAP) of at least 25 mm Hg, after eliminating those with postcapillary PH, the authors concluded that 36% of their cohort had precapillary PH. In addition, these same patients tended to have lower fraction of expiratory volume in 1 second values and higher rates of hypoxemia with lower 6-minute walk test performances. In other words, in more progressive disease, there is elevation of PAPs.22 The reason for this rise in PAP is likely multifactorial, resulting from a combination of hypoxia, hypercapnea, and parenchymal damage leading to loss of pulmonary vessels.23 Patients with interstitial lung disease (ILD) display a similar relationship between PH and severity of pulmonary disease, albeit with greater variability. Similar to chronic obstructive pulmonary disease (COPD), PH resulting from ILD carries a significant reduction in life expectancy urging some authors to conclude that these patients should be promptly listed for transplantation.24


Regardless of the etiology, this increase in RV afterload can result in varying degrees of dysfunction of the RV. Predominantly, this effect takes the form of hypertrophy of the RV with preserved systolic function, largely attributable to the slow rise in PA pressures allowing the RV to remodel. In fact, up to two-thirds of patients with COPD have evidence of this RV remodeling on autopsy.25 Hilde and partners in 2013 showed compelling evidence that even minimal elevations of pulmonary vascular resistance and MPAP resulted in RV remodeling, dilation, and subsequently reduced RV systolic function. In addition, these investigators showed a distinct relationship between MPAP and worsening RV ­performance indices.26


Anatomically, the RV differs from the LV in its shape and structure. Instead of a thick-walled, round structure, the RV is a thin-walled conical structure that wraps around the LV septum. This structure can functionally be divided into three parts. The inlet is bordered by the tricuspid annulus, the chordae and the associated papillary muscles, the apex is made of heavily trabeculated muscle and the outlet which is essentially the smooth muscle RV outflow tract (RVOT). The function of the RV is largely dependent on systemic venous return providing preload and resistance of the balance between the pulmonary vessels providing RV afterload. These forces combine with the intrinsic contractility of the RV free wall and interventricular septum to generate RV output. RV stroke work requires much less work compared with the LV, as is evident from the pressure volume loops of the RV. These loops display a lack of isovolumetric contraction and show lower peak systolic pressures as well as simply existing at higher baseline volume levels.27 This makes the RV relatively sensitive to physiologic perturbations.


To adequately evaluate the RV, the physician must obtain multiple views of this chamber to perform Doppler measurements, as well as anatomic measurements. These views are best obtained in the ME-4C, mid-esophageal RV inflow-outflow (MERV in-out), transgastric short axis (TG-SAX), and the transgastric RV inflow-outflow (TGRV ­in-out) (Fig. 55.3).


image
• Fig. 55.3 The midesophageal right ventricular (RV) inflow-outflow and the transgastric RV inflow view that will be used in the tricuspid annular plane systolic excursion and RVs measurements. ATML, anterior valve leaflet; AV, aortic valve; AW, anterior wall; LA, left atrium; PA, pulmonary artery; PTVL, posterior valve leaflet; PW, pericardial wall; RA, right atrium; RV, right ventricle; RVOT, right ventricular outflow tract. (Reproduced with permission from pie.med.utoronto.ca/tee.)

From the ME-4C view a good assessment of RV function and size can be made. In this view the RV and LV are clearly observed and the relationship of one chamber to the other can be seen. In the ME-4C view, it is easy to obtain quantification of the end-diastolic area (EDA), as well as the end-systolic area (ESA). The fractional area of change (FAC) is then defined as: (RVEDA-RVESA/RVEDA)×100. These areas are obtained by pausing the frame at the requisite point in the cardiac cycle, taking care to ensure the RV is not foreshortened and includes the apex. It is then possible to trace to RV chamber, including the trabeculae.28 The normal value for an RV FAC is at least 35% with values under this being indicative of varying degrees of right ventricular systolic dysfunction. One limitation of this method is the likely exclusion of the RVOT which contributes at least something to the RV systolic function. The benefit, however, is that this method takes into account both longitudinal, as well as free wall contraction, thus ensuring that FAC correlates well with ejection fraction (EF) elucidated through magnetic resonance imaging (MRI).29,30


Also from the ME-4C view it is possible to assess RV size and shape, and relationship to the LV. The RV should appear more wedge-like as opposed to the rounded LV, with its size being roughly two-thirds that of the LV. The dilated RV will make up progressively more of the apex of the heart, as well as approach the same size as the LV. At end diastole, the areas of the two chambers are easily measured and any RV:LV ratio over 1 indicates severe dilation. As the RV dilates and becomes overloaded with pressure and/or volume, the interventricular septum shifts leftward and in the TG-SAX view will appear flattened with the LV appearing D-shaped. This shift results in two detrimental effects resulting in decreased cardiac output. First, the shift of the septum into the LV decreases this chamber size, reducing the LV end diastolic volume (LVEDV) and thus stroke volume. Second, the shift of the intraventricular septum reduces the contractility of the septum, a force that the RV depends on for its systolic performance.30


Also in the ME-4C view, many physicians will attempt to measure the systolic excursion of the tricuspid valve (TV), otherwise referred to as tricuspid annular plane systolic excursion (TAPSE). This has a been a long validated method for assessing RV function in the TTE, though it has been thought to be somewhat limited in the TEE because of its dependence on obtaining a view in which the motion mode (MMode) Doppler beam could be in good alignment with the TV motion. However, there are some ways to overcome this perceived limitation and obtain a reliable TAPSE measurement.31 Some physicians choose to make up for the poor alignment in postprocessing of the images and conducting nonlabeled measurements of the distance the tricuspid annulus moves in the cardiac cycle. Although onerous, this is one method to compensate for poor Doppler alignment. On modern machines, there is an adaptation of the traditional MMode called “anatomic MMode” corrects transducer position relative to the plane being measured. Korshin and colleagues in 2018 found that when in the TGRV in-out, anatomic MMode gave high precision and reproducibility with strong correlation to the TAPSE measured on TTE. The same method certainly can be used in the ME-4C view though with lower agreement with that of TTE.32 Although the TAPSE is widely accepted as a marker of RV performance, it is important to note how specific disease states, that are especially relevant in thoracic surgery, can influence the prognostic and clinical effect of the TAPSE measurement. Multiple investigators have shown that TAPSE correlates with survival in patients with congestive heart failure (CHF), with one series of over 1500 patients showing a cutoff of 15.9 mm, which means that in patients with CHF who have a TAPSE of less than 15.9 mm, there is poorer prognosis than those with a higher TAPSE value. Follow-up work has demonstrated that lower TAPSE values correlate with an increase in hospitalization rates and morbidity as well. In patients with COPD, the TAPSE has also been shown to correlate with poorer prognosis and higher morbidity as well (Table 55.2).33



Table 55.2





















These Methods of Right Ventricular Evaluation can Give Information Regarding the Performance of the Right Ventricle
Measure Measurement Normal Value
Tricuspid annular plane systolic excursion

Image

Measured in motion mode as distance between nadir and peak travel of lateral annulus of tidal volume >1.6 cm
Fractional area of change

Image

((EDA – ESA)/EDA) × 100 >35%
Longitudinal strain

Image

(Length in Systole – Length in Diastole)/Length in Diastole) More negative than –20

EDA, End-diastolic area; ESA, end-systolic area.


While in the ME-4C view, the physician can focus on the RV by moving it to the center of the field and ensuring to limit foreshortening as much as possible. Most new TEE machines are capable of directly measuring the contraction of myocardial muscle fibers by measuring the displacement of these muscle speckles through the cardiac cycle. By doing so, it is possible to accurately quantify the longitudinal contraction as it happens from the TV annulus to the infundibulum (or RVOT). Although an in-depth discussion of this technology is well beyond the capacity of this chapter, we will briefly review it. What are termed “speckles” are actually specific patterns of interference within the myocardium, these “speckles” are then able to be tracked over time to create a measurement of strain (strain = [length in systole ‒ length in diastole]/length in diastole). Thus as the RV free wall contracts longitudinally from the TV annulus to infundibulum. Given this, the strain measurement will be reported as a negative value with a cutoff of ‒20 or more negative being normal. Values less negative than ‒20 are considered abnormal. Two measurements of the RV can be obtained using this technique: global longitudinal strain (GLS) and free wall strain (FWS). Although both measures give a measure of longitudinal contraction, the GLS is the average value of all RV segments (3 free wall + the septum), whereas the FWS ignores the septal contribution. This technique is not angle dependent as in TAPSE; however, there is limitation when out of plane contraction is happening. This can be ameliorated by using new three-dimensional (3D) software that will measure “strain area” as opposed to longitudinal strain.34


The application of 3D technology to imaging the RV is relatively new, at least in the intraoperative setting. As with many RV measurements, there was concern about reproducibility and accuracy compared with TTE or MRI when extrapolating to the TEE and intraoperative setting. However, this has proven to be a valuable tool for evaluating the RV for both size and function. Fusini et al. reported a case series of 150 patients undergoing valve procedures in which the authors acquired 3D volumetric sets, which were then analyzed for RV end-systolic volume (ESV), RV end-diastolic volume (EDV), and RVEF, as well as two-dimensional (2D) measurements of FAC and TAPSE. Adequate data were acquired in 92.7% of patients and the 3D EF of these patients displayed high levels of correlation with both 2D FAC, as well as TAPSE, both of which have previously been validated compared to MRI.35 Subsequent work has confirmed not only the feasibility of acquiring 3D data of the RV, but also the reproducibility between observers. In addition, these data sets were again found to correlate well with 2D, TTE, and MRI measurements of RV function.36


As the RV dilates, there is outward force applied to the TV annulus. This force changes the ellipsoid TV into a more round shape, which results in the leaflets being pulled apart leading to poor coaptation and tricuspid regurgitation (TR). It is not uncommon to see this sequence evolve acutely from pressure overload, as happens in PE, resulting in even minimal elevations of MPAP. Importantly, the degree of TR does not necessarily correlate with the degree of RV dysfunction. As the RV dilates and the function decreases the force generated will be lessened leading to a reduction in TR velocity and jet size, making this a relatively poor marker of RV performance.37,38



Patent Foramen Ovale


Although generally benign, patent foramen ovale (PFO) has been implicated in stroke and hypoxemia. Under normal loading conditions, the LA pressure exceeds that of the RA, creating a left to right shunt. With the rare exception, this is generally very well tolerated and inconsequential. With elevated right atrial (RA) pressure, there exists the possibility to reverse this intracardiac shunt from the RA through the PFO into the left atrium (LA). In the case of stroke, there are several mechanisms by which PFO is thought to be implicated. First, the PFO may serve as the path of least resistance with right to left shunting and this flow may carry with it embolic material, such as microemboli, air, or thrombus. Second, in a certain portion of patients, the PFO is associated with atrial septum aneurysm which may serve as the nidus for thrombus formation. These septal aneurysms are rare in the general population; however, they are reported on autopsy in a disproportionately high portion of patients who suffered stroke. Although somewhat peripherally related, PFO may predispose patients to atrial arrhythmias which in of themselves raise the risk of stroke.39 Regardless of the mechanism, stroke can be a potentially devastating complication of noncardiac surgery. Unfortunately, this complication is much more prevalent in patients with preexisting atrial septal defect (ASD) or PFO. In one case series of over 600,000 noncardiac surgeries in patients who had preoperative echocardiograms, roughly 9000 patients were found to have a PFO or ASD. Over 40,000 strokes occurred perioperatively; however, 35% of those with a preexisting PFO/ASD suffered stroke compared with 6% of those with intact atrial septums.40


Another possible outcome of a PFO and the creation of a right to left shunt is hypoxia. Through this shunt, venous blood can mix with arterial blood, leading to a hypoxemic mixture. This is in turn can result in PH.41 This mechanism has been implicated in some postthoracic surgery patients who develop hypoxia. Likely, this shunt results from increased RV afterload because of resection of pulmonary vascular beds, combined with some degree of fluid overload during surgery which can reduce RV function. These factors increase right-sided filling pressures creating the left to right shunt that contributes to hypoxia.42 In addition, intraoperatively, the RA pressure may acutely increase as a result of one-lung ventilation induced hypercarbia raising PAP, or following clamping of the PAs.


As stated previously, a PFO is a generally irrelevant condition that is present in varying rates depending on age. In their work from 1984, Hagen and colleagues examined the hearts of 965 patients on autopsy. They found that the incidence of PFO overall was 27.3% with a range from 34.3% in the first 3 decades of life to 20.2% in the ninth and 13th decade of life.43 These defects arise because of the failure of the primum and secundum to adhere, leaving a small passageway between the two chambers. Immediately after birth, the orifice in the muscular septum primum is covered by the mobile, more fibrous, septum secundum, and the sudden rise of LA pressure should force the two septal components against one another, allowing fusion over subsequent years. TEE with agitated saline performs well in detecting these lesions with sensitivity approaching 90% and specificity of roughly 91%.44


An examination intended to investigate for the presence of PFO will begin in the ME-4C view, however, 2D evaluation is unlikely to display a visually detectable PFO. The addition of color flow Doppler with the Nyquist limit of between 45 and 55cm/s will allow the physician to see evidence of flow across the septum, indicating shunting. To fully evaluate the septum for integrity, it must scan through the septum by increasing the omniplane from 0 to 130 degrees to ensure visualization of the entire structure. Ultimately, the highest sensitivity is obtained by the addition of contrast; in this setting this would be the addition of agitated saline to perform a “bubble study.” Under normal loading conditions, LA pressure is greater than RA pressure, which would prevent transit through an atrial septal defect if one existed. To overcome this, a Valsalva maneuver should be applied during injection of the agitated saline, the sudden release of the Valsalva will acutely raise the preload on the RA thus increasing the RA pressure. If a PFO exists, bubbles will be seen traversing the septum and appearing in the LA.


The decision on whether or not to close an intraoperatively identified PFO is somewhat unclear at this point. Largely, there is a paucity of data examining whether to close these defects when incidentally found during surgery, and even less data indicating the preferred method of closure. The clinical significance of these PFOs is unclear and the decision of whether or not to close them appears to be dependent on surgeon preference, probability of hypoxia, and whether or not there will be a deviation in the surgical plan to accomplish this closure.45 Those patients whose atria were already opened, mitral valve (MV) or TV repairs, and those who were younger or with prior history of stroke/transient ischemic attack were most likely to have their PFO repaired. However, there is some evidence that stroke rates increased following the repair of incidentally found PFOs.46 This is in contrast to closure of PFOs found in patients having cryptogenic strokes. In this patient population, percutaneous closure of the septal defect has led to a lower rate of recurrent strokes when compared to those who only received medical therapy.47


In summary, PFO are common defects that may increase the risk of stroke in the population, though closing incidentally found PFOs appear not to reduce this risk. Intraoperatively, PFO or ASD may result in right to left shunting as the RV loading conditions change which may result in hypoxia (Fig. 55.4).


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• Fig. 55.4 A: Two-dimensional imaging reveals the interatrial septum (IAS) with possible defect, B: color flow Doppler (CFD) confirms this defect and can show directionality of the shunt. C: An agitated saline study can readily show right to left shunting as the bubbles traverse the IAS quick than if they had cycled through the body first. D: Finally, three-dimensional imaging can provide highly resolute images of the defect. LA, left atrium; PFO, patent foramen ovale; RA, right atrium. (From Chen Z, Li C, Li Y, Tang H, Rao Li, Wang M. Concomitant coronary and pulmonary embolism associated with patent foramen ovale: a case report. Medicine. 2017;96; E9480.)

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Oct 6, 2021 | Posted by in ANESTHESIA | Comments Off on Transesophageal Echocardiography in Noncardiac Thoracic Surgery
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