|Year : 2020 | Volume
| Issue : 1 | Page : 8-12
Computed tomography as an alternative to transesophageal echocardiography: A review of the literature in light of COVID-19
Michael J Accavitti, Sorin Danciu
Department of Cardiology, Advocate Illinois Masonic Medical Center, Chicago, IL, USA
|Date of Submission||29-Apr-2020|
|Date of Acceptance||02-May-2020|
|Date of Web Publication||16-Jun-2020|
Dr. Michael J Accavitti
C/O Department of Cardiology, 836 W Wellington Ave, Chicago 60657, IL
Source of Support: None, Conflict of Interest: None
During the outbreak of coronavirus disease 2019 (COVID-19) in the spring of 2020, the CDC recommended health-care providers limit performing aerosol-producing procedures when possible. Transesophageal echocardiography (TEE) is a procedure used frequently for both procedural and nonprocedural cardiac imaging. The performance of a TEE requires not only for physicians and staff to be physically close to the mouths of potentially infected patients, but also involves aerosol generating activities such as airway suctioning. In addition, intubation with TEE probe can cause coughing. Cardiac computed tomography (CT) is an imaging modality that does not increase COVID-19 exposure risk to cardiology staff and physicians. In this article, we review the most common indications for TEE and discuss the data supporting the viability of using cardiac CT as an alternative to TEE.
Keywords: Computed tomography, coronavirus, transesophageal echocardiography
|How to cite this article:|
Accavitti MJ, Danciu S. Computed tomography as an alternative to transesophageal echocardiography: A review of the literature in light of COVID-19. Ann Clin Cardiol 2020;2:8-12
|How to cite this URL:|
Accavitti MJ, Danciu S. Computed tomography as an alternative to transesophageal echocardiography: A review of the literature in light of COVID-19. Ann Clin Cardiol [serial online] 2020 [cited 2020 Nov 28];2:8-12. Available from: http://www.onlineacc.org/text.asp?2020/2/1/8/286471
| Introduction|| |
Transesophageal echocardiography (TEE) is a frequently performed cardiac imaging procedure; indications for TEE are diverse and include data acquisition as well as procedural guidance. In the spring of 2020, coronavirus disease 2019 (COVID-19), a novel coronavirus, became a global pandemic infecting millions of people through physical contact and exposure to respiratory droplets. Medical workers are at a particularly increased risk for transmission given the need for proximity to patients and the performance of aerosol-generating procedures. In April 2020, the American Society of Echocardiography (ASE) provided a statement on the protection of patients and service providers during the COVID-19 outbreak. The ASE statement recommends “TEEs should be postponed or canceled if an alternative imaging modality can provide necessary information.” We endeavor in this article to review the most common nonprocedural indications for TEE and review the available literature supporting the use of cardiac computed tomography (CT) in its place.
| Data Acquisition|| |
The authors performed a thorough, though not exhaustive, review of available literature. When available, we favored meta-analyses and head-to-head trials. Sources cited in guidelines and appropriate use documents were also favored. Additional resources were discovered using the PubMed search portal in April 2020.
| Study Protocols|| |
We would like to make a special note that many of these studies rely on particular CT acquisition and contrast administration protocols. Although this is not the focus of this article, studies cited herein may not have achieved their results with standard CT angiography (CTA) protocols, and translation to clinical practice may require modifications to standard protocols.
| Exclusion of Left Atrial Appendage Thrombus|| |
Assessment of left atrial appendage thrombus using cardiac CT is a well-studied method. A 2013 meta-analysis demonstrated a mean sensitivity of 96% and a specificity of 92% for the detection of thrombus. This led to an excellent negative predictive value, 99%, but a suboptimal positive predictive value, 41%. The introduction of a double-phase CT protocol drastically improved specificity to 92%, reducing error secondary to nonuniform opacification of the appendage [Figure 1]. As the primary concern for imaging the left atrial appendage is to rule out the presence of a thrombus prior to cardioversion, the excellent negative predictive value for cardiac CT makes it a viable alternative modality in the place of TEE.
|Figure 1: Computed tomography detection of left atrial appendage thrombus|
Click here to view
| Intracardiac Masses|| |
Intracardiac masses are often detected incidentally by routine echocardiography or on chest imaging performed for an unrelated indication. The most commonly detected mass is the atrial myxoma, representing 50% of all primary cardiac neoplasms. One goal of TEE in these patients is to identify a connecting stalk which is often too small to be identified on CT. Instead, CT provides excellent localization of the mass, with involvement of the interatrial septum and fossa ovalis offering a high degree of confidence in diagnosis. In a 2014 study, Shin et al. examined the sensitivity and specificity for the detection of myxoma on CT and found a result of 87% and 97%, respectively. TEE has a reported sensitivity of 100%. Because many of these masses are incidental findings and because transthoracic echocardiography is 95% sensitive for myxoma, further testing is most often indicated for verification and surgical planning. The high specificity and good ability to localize is thus beneficial for CT.
In contrast to myxoma, fibroelastomas are small (generally <10 mm), avascular collections of dense connective tissue representing 10% of all primary cardiac tumors. Over 90% occur on valve surfaces, more often on the aortic and mitral than the pulmonic or tricuspid. Echocardiography is quite sensitive to these tumors because of their motion relative to their attached valve. Because of their small size and mobility, they are not well visualized on CT, and studies of fibroelastoma being detected by CT remain limited to case reports.
Further types of masses are increasingly rare. Most malignant tumors found in the heart are of noncardiac origin. Published studies are generally collections of descriptions and common CT findings. For all masses, CT offers data such as size, location, and morphology, but compared to TEE, CT offers greater detail on tissue characteristics such as calcification or fat attenuation. Differentiation of the types of masses by CT does not appear to have been compared to TEE.
| Endocarditis|| |
Several studies have been undertaken to evaluate the usefulness of CT in patients with suspected endocarditis. Feuchtner et al. in their 2009 study directly compared the performance of TEE and cardiac CT to surgical findings. In that study, CT was found to be 97% sensitive and 88% specific. More recent investigation using three-dimensional reconstructions of TEE compared to CT found lower sensitivity for CT, only 72%. In particular, CT was less sensitive to small (defined as <10 mm) vegetations, which were diagnosed only 52.8% of the time. Larger (>10 mm) lesions were much more likely, 89.7%, to be detected [Figure 2].
Of the studies reviewed, the rates of detection of endocarditis varied, but the 72% noted above was lower than most. Size of vegetation plays a role in the detection of any modality, but CT appears to be more likely to miss small lesions, maybe owing to the lack of associated flow information. All studies seemed to support the poor sensitivity and specificity of CT for leaflet perforation, while detection of abscess is superior with CT. Unfortunately, transthoracic echocardiography demonstrates poor sensitivity for valvular perforation, meaning it offers little assistance as an adjunctive noninvasive technique to CT.
A 2012 study by Fagman et al. examined agreement in findings between TEE and CT in suspected prosthetic aortic valve endocarditis. TEE was found to be more sensitive compared to CT, 100% and 93%, respectively, but findings in general demonstrated good agreement [Figure 3]. CT may offer benefit in terms of diagnosis owing to the significant amount of artifact in the echocardiography of prosthetic valves.
|Figure 3: Bioprosthetic aortic valve endocarditis with leaflet perforation and large anterior pseudoaneurysm|
Click here to view
| Source of Embolus After Cerebrovascular Accident|| |
Distinct from examination for specific pathology, the performance of TEE to examine for a source of embolism in patients with cerebrovascular accident (CVA) is a separate indication in itself. A recent meta-analysis in the Journal of Neurology pooled 14 studies and demonstrated a pooled sensitivity of CTA (to a reference TEE) of 86% and a pooled specificity of 97.4%. The authors did note a significant amount of heterogeneity between studies that made their analysis more challenging.
For patients who suffered a CVA, TEE is most often used for left atrial evaluation, atrial septal aneurysm, patent foramen ovale, and aortic atheroma. CT evaluation of patent foramen ovale has compared favorably to TEE. CT is able to detect shunt flow using contrast movement through the defect, the presence of contrast in the defect “tunnel,” and the presence of a defect from the interface of the tissue planes. Aortic atheroma represents another possible source of thrombus for patients with CVA which is examined during TEE. In a comparative trial, CT was able to identify the presence or absence of atheroma with 87% sensitivity and 82% specificity.
| Aortic Stenosis and Regurgitation|| |
While TTE provides superior evaluation of the velocities through the aortic valve, TEE is routinely used for further evaluation of the valve area. Aortic valve area (AVA) on cardiac CT has been shown to correlate with measurements obtained by TEE., Using TEE as the comparison standard, CT was 92% sensitive and 89% specific for the detection of severe aortic stenosis (AS). When examining moderate and severe AS (expanding AVA to <1.5 cm), the sensitivity increased to 97.8% and specificity to 91.7%. The authors note that, in general, CT tended to overestimate the AVA compared to TEE, but by <0.2 cm. In the current era of transcatheter aortic valve replacement, CT is used extensively for planning purposes. CT provides anatomic information, such as coronary heights, that cannot be obtained by TEE and therefore, is a required part of the valve replacement evaluation. In addition, aortic valve calcium scoring has become a routine part of evaluating low-flow AS. CT in this respect offers superior evaluation of the stenotic aortic valve.
Assessment of aortic regurgitation (AR) has also been studied as it relates to echocardiography. CT compares well to TTE in the diagnosis of moderate and severe regurgitation. Further comparison with TTE looked at mild, moderate, and severe regurgitation and noted that CT was 70% sensitive but 100% specific. Regurgitant orifice area correlated closely with echocardiography. In addition, CT provides volumetric assessment of regurgitant flow when AR is the only lesion being evaluated.
| Mitral and Tricuspid Valve Regurgitation|| |
The use of CT to diagnose mitral regurgitation has been demonstrated to be sensitive as well as specific, with mean regurgitant orifice areas correlating well with both TEE and ventriculography. In another study, CT assessment of isolated mitral regurgitation was compared to TTE and magnetic resonance imaging (MRI) where it again compared favorably, demonstrating similar regurgitant volume and regurgitant fraction, with no significant difference. Regurgitation of the tricuspid is more difficult to measure, and CT methods and approaches to quantify at this time are more experimental.
While measuring the flow of the tricuspid valve may not be a strong point of CT, it is able to offer excellent anatomic information for procedural planning. Similarly, CT of the mitral valve correlates well with TEE when determining valve morphology. In fact, many studies into mitral morphology comparing TEE to CT use CT as the reference standard. While TEE remains a critical part of the deployment of many valvular solutions, CT offers accurate information for preprocedural planning.
| Nondiagnostic Transthoracic Echocardiogram|| |
Compared to TTE, CT evaluation of global ejection fraction (EF) has been demonstrated to provide similar findings. Similar correlation was found in patients with reduced EF, which also found a close correlation with the detection of regional wall motion abnormalities. A 2015 meta-analysis comparing CT and TTE to MRI found that CT compared well to three-dimensional echocardiographic techniques and was superior to two-dimensional techniques. CT also compared well in the estimation of right ventricular (RV) EF. TEE presents several limitations when evaluating EF of the left ventricle (LV) owing to the proximity of the probe to the ventricle in the deep gastric window. Advancement of the probe into the gastric position can also increase patient discomfort and cause retching. Cardiac CT offers an accurate alternative modality in patients whose TTE is not diagnostic for LV and RV function.
| Aortic Pathology|| |
We previously discussed atheroma in the section on CVA, but TEE is also used to investigate for other aortic pathologies including dissection. A 1996 study compared TEE and CT as well as MRI. All the three modalities were 100% sensitive for thoracic dissection. CT offered equivalent specificity compared to TEE (100% vs. 94%). In addition, CT was statistically significantly (P < 0.05) more sensitive for the involvement of the aortic arch vessels (93% vs. 60%). Other studies have found similar quality between modalities with greater sensitivity for thrombus or abdominal aorta involvement with CT.
Under normal circumstances, TEE is also limited by the need for subspecialist availability to perform the study. In cases where time is available, CT has already become the preferred modality of emergency rooms because it offers comparable accuracy, can be performed quickly, and utilizes staff who are readily available. Intraoperative TEE remains a staple of management.
| Left Atrial Appendage Closure Device Planning|| |
While the coronavirus outbreak has caused many hospitals to pause elective procedures, CT may still allow patients awaiting left atrial appendage closure to complete their workup and determination of candidacy. Interestingly, CT and TEE have been noted to offer discrepant left atrial appendage orifice sizing. It has been theorized that CT may allow for more accurate prediction of device size, and that, compared to TEE, the sizing error tendency of CT may lead to fewer gross sizing errors.
| Conclusions|| |
While our review of the literature has certainly noted the superiority of TEE in some instances, broadly, cardiac CT offers a noninvasive method of evaluating for a majority of the most common indications for a TEE. While CT does introduce radiation risk to the patient, in light of the COVID-19 pandemic, it greatly reduces infection exposure risk to physicians and staff. Avoiding TEE also preserves sedation resources. Finally, given that COVID-19 is a respiratory illness best evaluated by CT, many hospitals have already established protocols for safe transport and cleaning to designated CT scanners. Pursuing cardiac CT, when reasonable, can further piggyback off these infection control efforts.
Financial support and sponsorship
Conflicts of interest
There are no conflicts of interest.
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[Figure 1], [Figure 2], [Figure 3]