Transesophageal echocardiogram

Transesophageal echocardiography
Transesophageal echocardiography
	TEE
MeSH	D017548
OPS-301 code	3-052
	[ edit on Wikidata]

Last updated July 11, 2024

A transesophageal echocardiogram (TEE; also spelled transoesophageal echocardiogram; TOE in British English) is an alternative way to perform an echocardiogram. A specialized probe containing an ultrasound transducer at its tip is passed into the patient's esophagus.^[1] This allows image and Doppler evaluation which can be recorded. It is commonly used during cardiac surgery and is an excellent modality for assessing the aorta, although there are some limitations.^[2]

Details

TEE is a semi-invasive procedure in that the probe must enter the body but does not require surgical (i.e., invasive) cutting for this procedure. Before inserting the probe, mild to moderate sedation is induced in the patient to ease the discomfort and to decrease the gag reflex. Usually a local anesthetic spray (e.g., lidocaine, benzocaine, xylocaine) is used for the back of the throat or as a jelly/lubricant anesthetic for the esophagus. Sedation and anesthesia are required to make the procedure tolerable and safer, as biting the probe, coughing, vomiting, and patient movement would drastically reduce the value of the procedure.^{[ citation needed ]}

Mild or moderate sedation can be induced with medications such as midazolam (a benzodiazepine with sedating, amnesiac qualities), fentanyl (an opioid), or propofol (a sedative/general anesthetic, depending on dosage). Children are anesthetized. Adults are sometimes anesthetized as well if moderate sedation is unsuccessful.^{[ citation needed ]}

Due to the procedure being invasive, sonographers do not perform this procedure unlike transthoracic echo.^{[ citation needed ]}

Once adequate sedation and anesthesia are achieved, the probe is passed through the mouth and into the esophagus. From here, the protocol used for the procedure is highly variable. As the study could be terminated any second (e.g., respiratory compromise, hypotension, intolerance to the probe) the structures of particular interest could be visualized first. For example, if the TEE is ordered to look for mitral regurgitation then the mitral valve may be fully inspected first. At the completion of the study, the probe is removed and patient is monitored for recovery from sedation.^{[ citation needed ]}

Advantages

The advantage of TEE over TTE is usually clearer images, especially of structures that are difficult to view transthoracically (through the chest wall). This difficulty with TTE is exemplified with obesity and COPD, as both of these can drastically limit both the window available and the quality of the images obtained through those windows This reduces the attenuation (weakening) of the ultrasound signal, generating a stronger return signal, ultimately enhancing image and Doppler quality. Comparatively, transthoracic ultrasound must first traverse skin, fat, ribs and lungs before reflecting off the heart and back to the probe before an image can be created. All these structures, along with the increased distance the beam must travel, weaken the ultrasound signal thus degrading the image and Doppler quality.^{[ citation needed ]}

In adults, several structures can be evaluated and imaged better with the TEE, including the aorta, pulmonary artery, valves of the heart, both atria, atrial septum, left atrial appendage, and coronary arteries. TEE has a very high sensitivity for locating a blood clot inside the left atrium.^[3]

TEE is also frequently used concurrently with cardiac surgery to provide immediate visualization, inspection, and monitoring of the patient throughout the procedure. Its intraoperative utility includes real-time hemodynamic monitoring by the cardiac anesthesiologist, evaluation of relevant cardiac pathologies before and after surgical repair, and immediate assessment of the success of surgical interventions after cardiopulmonary bypass. TEE can also evaluate for unintended complications from surgery, for example unintended injury to cardiac valves, the aorta, or other structures during the procedure.^[4]

Disadvantages

TEE has several disadvantages, although they should be weighed against its significant benefits. The patient must follow the ASA NPO guidelines^[5] (usually not eat anything for eight hours and not drink anything for two hours prior to the procedure). Rather than one sonographer, a TEE needs a team of medical personnel of at least one nurse to monitor/administer sedation and a physician to perform the procedure (a third physician/sonographer can be used to push buttons on the ultrasound machine). It takes longer to perform a TEE than a TTE. It may be uncomfortable for the patient, who may require general anesthesia at the extreme to perform a TEE safely. Due to being an invasive procedure often involving sedation, it is more technically difficult to perform and requires experience to do it well while maintaining safety.^{[ citation needed ]}

TEE is limited to available anatomy. For example, if the patient has esophageal varices, esophageal stricture, Barrett's esophagus, or other esophageal or stomach problems then this can increase the risk of a TEE significantly. Performing an esophagogastroduodenoscopy (EGD) beforehand may be necessary to visualize the anatomy for safety, which exposes the patient to a second procedure. The anatomy may result in prohibitive risk.^{[ citation needed ]}

With transthoracic echo, numerous measurements are taken to aid in diagnosis and grading of diseases. These normal ranges are not as well defined for TEE and so there is less accepted standards (e.g., left atrial enlargement).^{[ citation needed ]}

Some risks are associated with the procedure, such as esophageal perforation^[6] around 1 in 10,000,^[7] and adverse reactions to the medication.

Specialty medicine professional organizations recommend against using transesophageal echocardiography to detect cardiac sources of embolization after a patient's health care provider has identified a source of embolization and if that person would not change a patient's management as a result of getting more information.^[8] Such organizations further recommend that doctors and patients should avoid seeking transesophageal echocardiography only for the sake of protocol-driven testing and to agree to the test only if it is right for the individual patient.^[8]

Clinical uses

In addition to use by cardiologists in outpatient and inpatient settings, TEE can be performed by a cardiac anesthesiologist to evaluate, diagnose, and treat patients in the perioperative period. Most commonly used during open heart procedures, if the patient's status warrants it, TEE can be used in the setting of any operation. TEE is very useful during many cardiac surgical procedures (e.g., mitral valve repair). It is actually an essential monitoring tool during this procedure. It helps to detect and quantify the disease preoperatively as well as to assess the results of surgery immediately after the procedure. If the repair is found to be inadequate, showing significant residual regurgitation, the surgeon can decide whether to go back to cardiopulmonary bypass to try to correct the defect. Aortic dissections are another important condition where TEE is very helpful. TEE can also help the surgeon during the insertion of a catheter for retrograde cardioplegia.^{[ citation needed ]}

Probes

TEE probes are similar in style to those used for esophagogastroduodenoscopy except the probe contains an ultrasound crystal rather than a visual camera. The ultrasound crystal images radially to the probe rather than axially (along the probe length) as the heart is not inline with the esophagus, but rather adjacent (anterior) to it.^{[ citation needed ]}

Angle

Most TEE probes contain a two-dimensional ultrasound crystal. This permits rotation of the 2-D echo plane without physical movement of the probe. This is often referred to the "angle" and varies between 0° and 180° (flipped image of 0°). For any given position of the probe in the body, different angles permit viewing structures more optimally.^{[ citation needed ]}

The angle can be adjusted with buttons or a dial, and this varies with the specific probe and ultrasound machine.^{[ citation needed ]}

Movement

The probes often have one or two degrees of freedom:^{[ citation needed ]}

Flexion or retroflexion can point the crystal superiorly or inferiorly, respectively
Left and right flexion tilts the probe left and right

These two degrees are typically adjusted using dials on the handle of the probe. A third degree is axial rotation of the probe (clockwise or counter-clockwise) and is present regardless of the other two degrees of freedom. A fourth degree is the translation of the probe long its axis to permit passing through the mouth, into the esophagus, and into the stomach.

The combination of these four degrees of freedom permit 2-D, color, and Doppler echo of practically every structure in the heart.

Positions

Transthoracic echo is far more commonly used than TEE and transthoracic echo is limited to by the available windows through the chest wall to visualize the heart. TEE does not have such discrete locations and can visualize the heart anywhere along the esophagus to the stomach. With that said, there are commonly accepted positions along this path that are used when performing a standard TEE.^{[ citation needed ]}

Midesophageal

The midesophageal view is positioned posterior from the left atrium and at 0° this provides for a long-axis four chamber view.^{[ citation needed ]}

At 0°, the long-axis four chamber view can be obtained with slight retroflexion of the probe. However, slight rotation and insertion may be needed to better visualize the right heart and tricuspid valve.

At 45°, the short-axis view of the aortic valve can be obtained. At this angle, a short-axis view of the right ventricle can be seen to visualize the right atrium, tricuspid valve, right ventricle, and pulmonary valve in a single view.

At 90°, the probe can be rotated clockwise to obtain the "bicaval view" in which the right atrial and both the inferior and superior vena cava can be viewed.

At 135°, the long-axis view of the aortic valve can be obtained.

The left atrial appendage, with proper probe positioning, can be visualized at all angles and often visualized at 0*, 45°, 90°, and 135° to adequately rule out a thrombus.

0° four chamber
45° aortic valve short-axis
90° two chamber
135° aortic valve long-axis

Transgastric

Pushing the TEE probe past the gastroesophageal junction into the stomach and flexing the probe (pointing it toward the superior) yields a short-axis view of the heart.

At 0°, the short-axis of the left ventricle can be obtained to see wall motion in the basal, mid, and distal sections.

If the probe is rotated clockwise, then the right heart and tricuspid valve can be visualized.

It is in the transgastric position that is best used to quantify the aortic valve with pulse- and continuous-wave Doppler as this is the best view to be best coaxial with the valve.

Upper esophagus

Pulling back of the TEE probe higher into the esophagus reveals the aortic arch. Typically, in the midesophageal view the probe is rotated until the descending aorta is visualized. Pulling back the probe permits visualization of the aorta and any atheromatous plaques within the aorta. Short axis visualization at 0° allows for descending aorta size measurements. Further pulling back will eventually reach the aorta arch and clockwise rotation will bring the arch into view. Continuous visualization of the aorta to the arch level can visualize coarctation of the aorta.^{[ citation needed ]}

Aortic arch

History

The transesophageal echocardiogram was first invented by Dr. Leon Frazin in 1974 while working at the Loyola University Stritch School of Medicine, Maywood, and Veterans Administration Hospital, Hines, Illinois. His early findings were published in 1976 in Circulation ^[9]

Diseases

While TEE can be used to answer many questions that a transthoracic echo can answer, the TEE is used for some diseases in particular.^{[ citation needed ]}

Infective endocarditis to get better quality images of the affected valve and better plan surgery, or need for surgery
Aortic root abscess, which generally is not visible on transthoracic echo
Eccentric mitral regurgitation can be better appreciated on TEE due to Coandă effect
Left atrial appendage thrombus and evaluation, follow up, and insertion of a left atrial appendage occlusion device
Evaluation for patent foramen ovale and atrial septal defect after a stroke, and insertion of a PFO/ASD plug
Monitoring during a procedure to cross the interatrial septum safely without poking the needle through an undesired structure
During cardiothoracic surgery for numerous procedures including immediately before and after replacement of a valve

Related Research Articles

Heart sounds are the noises generated by the beating heart and the resultant flow of blood through it. Specifically, the sounds reflect the turbulence created when the heart valves snap shut. In cardiac auscultation, an examiner may use a stethoscope to listen for these unique and distinct sounds that provide important auditory data regarding the condition of the heart.

The aortic valve is a valve in the heart of humans and most other animals, located between the left ventricle and the aorta. It is one of the four valves of the heart and one of the two semilunar valves, the other being the pulmonary valve. The aortic valve normally has three cusps or leaflets, although in 1–2% of the population it is found to congenitally have two leaflets. The aortic valve is the last structure in the heart the blood travels through before stopping the flow through the systemic circulation.

Aortic dissection (AD) occurs when an injury to the innermost layer of the aorta allows blood to flow between the layers of the aortic wall, forcing the layers apart. In most cases, this is associated with a sudden onset of severe chest or back pain, often described as "tearing" in character. Vomiting, sweating, and lightheadedness may also occur. Damage to other organs may result from the decreased blood supply, such as stroke, lower extremity ischemia, or mesenteric ischemia. Aortic dissection can quickly lead to death from insufficient blood flow to the heart or complete rupture of the aorta.

Echocardiography, also known as cardiac ultrasound, is the use of ultrasound to examine the heart. It is a type of medical imaging, using standard ultrasound or Doppler ultrasound. The visual image formed using this technique is called an echocardiogram, a cardiac echo, or simply an echo.

<span class="mw-page-title-main">Atrial septal defect</span> Human heart defect present at birth

Atrial septal defect (ASD) is a congenital heart defect in which blood flows between the atria of the heart. Some flow is a normal condition both pre-birth and immediately post-birth via the foramen ovale; however, when this does not naturally close after birth it is referred to as a patent (open) foramen ovale (PFO). It is common in patients with a congenital atrial septal aneurysm (ASA).

Bicuspid aortic valve (BAV) is a form of heart disease in which two of the leaflets of the aortic valve fuse during development in the womb resulting in a two-leaflet (bicuspid) valve instead of the normal three-leaflet (tricuspid) valve. BAV is the most common cause of heart disease present at birth and affects approximately 1.3% of adults. Normally, the mitral valve is the only bicuspid valve and this is situated between the heart's left atrium and left ventricle. Heart valves play a crucial role in ensuring the unidirectional flow of blood from the atrium to the ventricles, or from the ventricle to the aorta or pulmonary trunk. BAV is normally inherited.

<span class="mw-page-title-main">Aneurysm of sinus of Valsalva</span> Medical condition

Aneurysm of the aortic sinus, also known as the sinus of Valsalva, is a rare abnormality of the aorta, the largest artery in the body. The aorta normally has three small pouches that sit directly above the aortic valve, and an aneurysm of one of these sinuses is a thin-walled swelling. Aneurysms may affect the right (65–85%), non-coronary (10–30%), or rarely the left coronary sinus. These aneurysms may not cause any symptoms but if large can cause shortness of breath, palpitations or blackouts. Aortic sinus aneurysms can burst or rupture into adjacent cardiac chambers, which can lead to heart failure if untreated.

Aortic valve replacement is a cardiac surgery procedure whereby a failing aortic valve is replaced with an artificial heart valve. The aortic valve may need to be replaced because of aortic regurgitation, or if the valve is narrowed by stenosis.

<span class="mw-page-title-main">Cardiac catheterization</span> Insertion of a catheter into a chamber or vessel of the heart

Cardiac catheterization is the insertion of a catheter into a chamber or vessel of the heart. This is done both for diagnostic and interventional purposes.

A transthoracic echocardiogram (TTE) is the most common type of echocardiogram, which is a still or moving image of the internal parts of the heart using ultrasound. In this case, the probe is placed on the chest or abdomen of the subject to get various views of the heart. It is used as a non-invasive assessment of the overall health of the heart, including a patient's heart valves and degree of heart muscle contraction. The images are displayed on a monitor for real-time viewing and then recorded.

Endoscopic ultrasound (EUS) or echo-endoscopy is a medical procedure in which endoscopy is combined with ultrasound to obtain images of the internal organs in the chest, abdomen and colon. It can be used to visualize the walls of these organs, or to look at adjacent structures. Combined with Doppler imaging, nearby blood vessels can also be evaluated.

Cardiothoracic anesthesiology is a subspeciality of the medical practice of anesthesiology, devoted to the preoperative, intraoperative, and postoperative care of adult and pediatric patients undergoing cardiothoracic surgery and related invasive procedures.

Injury of the thoracic aorta refers to any injury which affects the portion of the aorta which lies within the chest cavity. Injuries of the thoracic aorta are usually the result of physical trauma; however, they can also be the result of a pathological process. The main causes of this injury are deceleration and crush injuries. There are different grades to injuries to the aorta depending on the extent of injury, and the treatment whether surgical or medical depends on that grade. It is difficult to determine if a patient has a thoracic injury just by their symptoms, but through imaging and a physical exam the extent of injury can be determined. All patients with a thoracic aortic injury need to be treated either surgically with endovascular repair or open surgical repair or with medicine to keep their blood pressure and heart rate in the appropriate range. However, most patients that have a thoracic aortic injury do not live for 24 hours.

Double aortic arch is a relatively rare congenital cardiovascular malformation. DAA is an anomaly of the aortic arch in which two aortic arches form a complete vascular ring that can compress the trachea and/or esophagus. Most commonly there is a larger (dominant) right arch behind and a smaller (hypoplastic) left aortic arch in front of the trachea/esophagus. The two arches join to form the descending aorta which is usually on the left side. In some cases the end of the smaller left aortic arch closes and the vascular tissue becomes a fibrous cord. Although in these cases a complete ring of two patent aortic arches is not present, the term ‘vascular ring’ is the accepted generic term even in these anomalies.

Cardiac imaging refers to minimally invasive imaging of the heart using ultrasound, magnetic resonance imaging (MRI), computed tomography (CT), or nuclear medicine (NM) imaging with PET or SPECT. These cardiac techniques are otherwise referred to as echocardiography, Cardiac MRI, Cardiac CT, Cardiac PET and Cardiac SPECT including myocardial perfusion imaging.

<span class="mw-page-title-main">Hybrid cardiac surgery</span>

A hybrid cardiac surgical procedure in a narrow sense is defined as a procedure that combines a conventional, more invasive surgical part with an interventional part, using some sort of catheter-based procedure guided by fluoroscopy imaging in a hybrid operating room (OR) without interruption. The hybrid technique has a reduced risk of surgical complications and has shown decreased recovery time. It can be used to treat numerous heart diseases and conditions and with the increasing complexity of each case, the hybrid surgical technique is becoming more common.

A quadricuspid aortic valve (QAV) is a rare congenital heart defect characterized by the presence of four cusps, instead of the usual three found normally in the aortic valve. It is a defect that occurs during embryological development of the aortic trunk during gestation. There is an increased risk of developing post-natal aortic regurgitations and other heart-related diseases; therefore patients with the condition should be carefully monitored.

Numerical manipulation of Doppler parameters obtain during routine Echocardiography has been extensively utilized to non-invasively estimate intra-cardiac pressures, in many cases removing the need for invasive cardiac catheterization.

In medicine, Esophageal Doppler or Oesophageal Doppler uses a small ultrasound probe inserted into the esophagus through the nose or mouth to measure blood velocity in the descending aorta. It is minimally invasive and is used to derive hemodynamic parameters such as stroke volume (SV) and cardiac output (CO). A properly constructed and calibrated probe is approved for use on adults and children in many parts of the world.

Intracardiac echocardiography (ICE) is a specialized form of echocardiography that utilizes an ultrasound-tipped catheter to perform imaging of the heart from within the heart. Unlike transthoracic echocardiography (TTE), ICE is not limited by body habitus. An ICE catheter is inserted into the body, typically, through the femoral vein and advanced into the heart.

References

↑ Transesophageal+Echocardiography at the U.S. National Library of Medicine Medical Subject Headings (MeSH)
↑ Moeller, Shaun, Serbanescu, Mara, Abernathy, James, et al. "The Epiaortic Ultrasound Diagnosis of Iatrogenic Subadventitial Hematoma". A A Pract. 2020;14(13):e01333. doi : 10.1213/XAA.0000000000001333.
↑ Abdulla, Dr. Abdulla M. "Welcome to HeartSite.com". www.heartsite.com. Retrieved 12 April 2018.
↑ Hahn RT, Abraham T, Adams MS, Bruce CJ, Glas KE, Lang RM, Reeves ST, Shanewise JS, Siu SC, Stewart W, Picard MH (September 2013). "Guidelines for performing a comprehensive transesophageal echocardiographic examination: recommendations from the American Society of Echocardiography and the Society of Cardiovascular Anesthesiologists". J Am Soc Echocardiogr. 26 (9): 921–64. doi:10.1016/j.echo.2013.07.009. PMID 23998692.
↑ "Practice Guidelines for Preoperative Fasting and the Use of Pharmacologic Agents to Reduce the Risk of Pulmonary Aspiration". ASA Publications. Retrieved August 9, 2019.
↑ Ramadan AS, Stefanidis C, Ngatchou W, LeMoine O, De Canniere D, Jansens JL (September 2007). "Esophageal stents for iatrogenic esophageal perforations during cardiac surgery". Ann. Thorac. Surg. 84 (3): 1034–6. doi: 10.1016/j.athoracsur.2007.04.047 . PMID 17720433.
↑ Min JK, Spencer (September 18, 2005). "Clinical features of complications from transesophageal echocardiography: a single-center case series of 10,000 consecutive examinations". J Am Soc Echocardiogr. 18 (9): 925–929. doi:10.1016/j.echo.2005.01.034. PMID 16153515.
1 2
American Society of Echocardiography (20 December 2012), "Five Things Physicians and Patients Should Question", Choosing Wisely: an initiative of the ABIM Foundation , American Society of Echocardiography , retrieved February 27, 2013
, which cites
- Douglas, P. S.; Garcia, M. J.; Haines, D. E.; Lai, W. W.; Manning, W. J.; Patel, A. R.; Picard, M. H.; Polk, D. M.; Ragosta, M.; Ward, R. P.; Douglas, R. B.; Weiner, R. B.; Society for Cardiovascular Angiography Interventions; Society of Critical Care Medicine; American Society of Echocardiography; American Society of Nuclear Cardiology; Heart Failure Society of America; Society for Cardiovascular Magnetic Resonance; Society of Cardiovascular Computed Tomography; American Heart Association; Heart Rhythm Society (2011). "ACCF/ASE/AHA/ASNC/HFSA/HRS/SCAI/SCCM/SCCT/SCMR 2011 Appropriate Use Criteria for Echocardiography". Journal of the American College of Cardiology. 57 (9): 1126–1166. doi: 10.1016/j.jacc.2010.11.002 . PMID 21349406.
↑ Frazin, Leon (July 1976). "Esophageal Echocardiography". Circulation. 54 (1): 102–108. doi: 10.1161/01.CIR.54.1.102 . PMID 1277411. S2CID 7801244.

External links

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[1] Transesophageal+Echocardiography at the U.S. National Library of Medicine Medical Subject Headings (MeSH)

[2] Moeller, Shaun, Serbanescu, Mara, Abernathy, James, et al. "The Epiaortic Ultrasound Diagnosis of Iatrogenic Subadventitial Hematoma". A A Pract. 2020;14(13):e01333. doi : 10.1213/XAA.0000000000001333.

[3] Abdulla, Dr. Abdulla M. "Welcome to HeartSite.com". www.heartsite.com. Retrieved 12 April 2018.

[pmid23998692-4] Hahn RT, Abraham T, Adams MS, Bruce CJ, Glas KE, Lang RM, Reeves ST, Shanewise JS, Siu SC, Stewart W, Picard MH (September 2013). "Guidelines for performing a comprehensive transesophageal echocardiographic examination: recommendations from the American Society of Echocardiography and the Society of Cardiovascular Anesthesiologists". J Am Soc Echocardiogr. 26 (9): 921–64. doi:10.1016/j.echo.2013.07.009. PMID 23998692.

[5] "Practice Guidelines for Preoperative Fasting and the Use of Pharmacologic Agents to Reduce the Risk of Pulmonary Aspiration". ASA Publications. Retrieved August 9, 2019.

[pmid17720433-6] Ramadan AS, Stefanidis C, Ngatchou W, LeMoine O, De Canniere D, Jansens JL (September 2007). "Esophageal stents for iatrogenic esophageal perforations during cardiac surgery". Ann. Thorac. Surg. 84 (3): 1034–6. doi: 10.1016/j.athoracsur.2007.04.047 . PMID 17720433.

[7] Min JK, Spencer (September 18, 2005). "Clinical features of complications from transesophageal echocardiography: a single-center case series of 10,000 consecutive examinations". J Am Soc Echocardiogr. 18 (9): 925–929. doi:10.1016/j.echo.2005.01.034. PMID 16153515.

[ASEfive-8] 1 2 American Society of Echocardiography (20 December 2012), "Five Things Physicians and Patients Should Question", Choosing Wisely: an initiative of the ABIM Foundation , American Society of Echocardiography , retrieved February 27, 2013, which cites
Douglas, P. S.; Garcia, M. J.; Haines, D. E.; Lai, W. W.; Manning, W. J.; Patel, A. R.; Picard, M. H.; Polk, D. M.; Ragosta, M.; Ward, R. P.; Douglas, R. B.; Weiner, R. B.; Society for Cardiovascular Angiography Interventions; Society of Critical Care Medicine; American Society of Echocardiography; American Society of Nuclear Cardiology; Heart Failure Society of America; Society for Cardiovascular Magnetic Resonance; Society of Cardiovascular Computed Tomography; American Heart Association; Heart Rhythm Society (2011). "ACCF/ASE/AHA/ASNC/HFSA/HRS/SCAI/SCCM/SCCT/SCMR 2011 Appropriate Use Criteria for Echocardiography". Journal of the American College of Cardiology. 57 (9): 1126–1166. doi: 10.1016/j.jacc.2010.11.002 . PMID 21349406.

[mwAR4] Douglas, P. S.; Garcia, M. J.; Haines, D. E.; Lai, W. W.; Manning, W. J.; Patel, A. R.; Picard, M. H.; Polk, D. M.; Ragosta, M.; Ward, R. P.; Douglas, R. B.; Weiner, R. B.; Society for Cardiovascular Angiography Interventions; Society of Critical Care Medicine; American Society of Echocardiography; American Society of Nuclear Cardiology; Heart Failure Society of America; Society for Cardiovascular Magnetic Resonance; Society of Cardiovascular Computed Tomography; American Heart Association; Heart Rhythm Society (2011). "ACCF/ASE/AHA/ASNC/HFSA/HRS/SCAI/SCCM/SCCT/SCMR 2011 Appropriate Use Criteria for Echocardiography". Journal of the American College of Cardiology. 57 (9): 1126–1166. doi: 10.1016/j.jacc.2010.11.002 . PMID 21349406.

[9] Frazin, Leon (July 1976). "Esophageal Echocardiography". Circulation. 54 (1): 102–108. doi: 10.1161/01.CIR.54.1.102 . PMID 1277411. S2CID 7801244.

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