Modified transesophageal echocardiography of the dissected thoracic aorta; a novel diagnostic approach
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Transesophageal echocardiography (TEE) is a key diagnostic modality in patients with acute aortic dissection, yet its sensitivity is limited by a “blind-spot” caused by air in the trachea. After placement of a fluid-filled balloon in the trachea visualization of the thoracic aorta becomes possible. This method, modified TEE, has been shown to be an accurate test for the diagnosis of upper aortic atherosclerosis. In this study we discuss how we use modified TEE for the diagnosis and management of patients with (suspected) acute aortic dissection.
Novel diagnostic approach of the dissected aorta
Modified TEE provides the possibility to obtain a complete echocardiographic overview of the thoracic aorta and its branching vessels with anatomical and functional information. It is a bedside test, and can thus be applied in hemodynamic instable patients who cannot undergo computed tomography. Visualization of the aortic arch allows differentiation between Stanford type A and B dissections and visualization of the proximal cerebral vessels enables a timely identification of impaired cerebral perfusion.
During surgery modified TEE can be applied to identify the true lumen for cannulation, and to assure that the true lumen is perfused. Also, the innominate- and carotid arteries can be assessed for structural integrity and adequate perfusion during multiple phases of the surgical repair.
Modified TEE can reveal the “blind-spot” of conventional TEE. In patients with (suspected) aortic dissection it is thus possible to obtain a complete echocardiographic overview of the thoracic aorta and its branches. This is of specific merit in hemodynamically unstable patients who cannot undergo CT. Modified TEE can guide also guide the surgical management and monitor perfusion of the cerebral arteries.
KeywordsTransesophageal echocardiography Aortic dissection Cardiothoracic surgery Cerebral monitoring
Acute aortic dissection (AD) is a life-threatening condition, which requires a prompt diagnosis to prevent morbidity and mortality. This necessitates sensitive and conclusive diagnostic tests. Transthoracic echocardiography is often the first test used since it is directly available, may reveal a proximal dissection, and can detect pericardial and pleural effusion [1, 2]. However, the focused screening for AD requires tests with a superior diagnostic accuracy, i.e. computed tomography (CT), magnetic resonance imaging (MRI) or transesophageal echocardiography (TEE) [3, 4].
Guidelines recommend the use of CT or MRI as the primary test in patients who are hemodynamically stable . Both modalities can accurately visualize an intimal tear, and complications can be detected, including aneurysmal widening of the aorta, pericardial and pleural effusion and involvement of coronary or distal arteries [3, 4, 5, 6]. A major limitation of both tests is the need to move patients out of the acute care environment. Moreover, CT is lacking the possibility of functional imaging, while the use of MRI is limited by its longer imaging-time and lower availability.
In hemodynamically instable patients, TEE is recommended as the primary test because it can be performed in the emergency care department or operating room [3, 4, 5]. Transesophageal echocardiography has the advantage of providing a quick overview of the heart and aorta with both anatomical and functional information. The diagnostic accuracy of TEE is considered inferior however compared to CT and MRI, mainly because of the impaired visualization of the distal ascending aorta and aortic arch caused by the interposition of the air-filled trachea [3, 4, 7, 8]. Indeed, limited dissections can be missed due to this so-called “blind-spot” .
We also routinely use modified TEE in patients with (suspected) AD. Most importantly, modified TEE provides the possibility to obtain a complete echocardiographic overview of the thoracic aorta and its branches in patients who cannot undergo CT. Second, modified TEE can guide essential steps in the surgical repair of the dissected aorta. In this study we discuss how we use modified TEE to aid the diagnosis and management of AD patients.
Technique of modified TEE
Modified TEE is compatible with additional modalities including color-Doppler and 3D imaging. Contraindications are similar as for conventional TEE, with the addition of tracheomalacia (e.g. in connective tissue diseases) and tracheal stenosis which may predispose to complications related to the balloon inflation.
Examination in (suspected) aortic dissection
In the majority of patients CT is used as the primary diagnostic test for AD, with (modified) TEE as a secondary test to assess the functional consequences of an aortic dissection. Therefore, modified TEE is usually performed in the operating room before sternotomy, although imaging can also be performed in the emergency room. First, TEE is used to identify aortic dilatation, aortic valve insufficiency, and pericardial or pleural effusion. Then, the proximal ascending aorta and descending aorta are screened for a dissection, followed by an attempt the visualize the upper thoracic aorta and its branches. Usually no echocardiographic window can be obtained however, and the procedure will continue with modified TEE.
Distal ascending aorta view
Aortic arch view
Aortic branch vessels view
During surgery for AD, modified TEE is used to guide the surgical management and to support cerebral monitoring. Specific attention is given to the perfusion of the branching vessels (i.e. the brachiocephalic- and carotid artery), which can be impaired because of a continuing dissection, obstruction by an intimal tear, or compression by an extravascular hematoma. The early detection of impaired cerebral perfusion allows for timely changes in the management, e.g. direct initiation of deep-hypothermic arrest, maintenance of a higher blood pressure and application of additional cerebral monitoring tools, e.g. bispectral index and near-infrared spectroscopy.
Limitations of modified TEE
Modified TEE has some limitations. First, experience with conventional TEE is a prerequisite and additional training should be considered since a learning curve exists. Second, the spatial resolution can be lower than in conventional TEE because of some scattering by the balloon. Finally, we already addressed the procedures to prevent false positive results. Despite these measures we are aware of one patient (female, 43 years) who underwent sternotomy because of a false positive finding with modified TEE. This patient was referred for surgery based on the suspicion of an AD on CT. During preoperative visualization of the thoracic aorta with modified TEE no intimal tear was confirmed, but a structure outside the aorta appeared as an extramural hematoma of the aortic arch. However, during intraoperative inspection this structure was revealed to be thymus tissue.
Modified TEE can reveal the “blind-spot” of conventional TEE. In patients with suspected acute aortic dissection it is thus possible to obtain a complete echocardiographic overview of the thoracic aorta and its branches with both anatomical and functional information. This may be specifically useful in hemodynamically unstable patients who cannot undergo CT. During surgery for aortic dissection, modified TEE can guide the surgical management and monitor perfusion of the cerebral arteries.
AD, acute aortic dissection; CT, computed tomography; TEE, transesophageal echocardiography
We thank Iskander Oord for his assistance with the draught of the figures.
WJK collected the images and created the first draft; LP participated in study design and helped to draft the manuscript; GBBB described the intraoperative procedures; AvH gave supervision for the study design and technical aspects of the (echocardiographic) diagnosis of acute aortic dissections; AN made the images, and supervised the study. All authors read and approved the final manuscript.
WJK received financial support for an E-learning course and congress presentation from Medical2Market B.V. AN holds stock in Medical2Market B.V., Zwolle, the Netherlands.
Consent for publication
Patients consented to publication of their data.
Ethics approval and consent to participate
Formal evaluation of the study was waived by our medical ethical committee.
Modified TEE long- and short axis (X-plane) view of the distal ascending aorta (DAA), showing an intimal tear. (MP4 2793 kb)
Modified TEE long- and short axis (X-plane) view of the distal ascending aorta (DAA) with color-Doppler showing differential flow in the true- and false lumen. (MP4 2737 kb)
Modified TEE aortic arch short-axis view in a patient with a normal aortic arch and flow pattern. (MP4 589 kb)
Modified TEE showing the innominate artery with an intimal tear and differential flow. (MP4 2327 kb)
Modified TEE video of a patient with Stanford type A aortic dissection with progression into the innominate artery, visualized in a 2D long-axis and short-axis view. (MP4 1524 kb)
Modified TEE video of a patient with Stanford type A aortic dissection with progression into the innominate artery, visualized in a 3D long-axis view. (MP4 2641 kb)
Modified TEE long- and short axis (X-plane) videos of the innominate artery before surgery, showing propagation of an intimal tear into the innominate artery with almost complete obstruction of the vessel with limited perfusion of the true lumen. (MP4 491 kb)
Modified TEE long- and short axis (X-plane) videos of the innominate artery after surgery showing a normal flow pattern during extracorporeal circulation; artefact in the long-axis view, which does not indicate a persistent dissection. (MP4 440 kb)
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