Intraoperative Echocardiography

Anatomy and Physiology

Anatomical Views

The transesophageal echocardiography (TEE) probe is inserted through the oropharynx into the esophagus. All of the described TEE views are obtained when the TEE probe is located in the esophagus or stomach. The echocardiographer is typically able to identify a variety of structures including the cardiac chambers, valves, lungs, liver, superior vena cava, inferior vena cava, hepatic vein, pulmonary veins, pulmonary arteries, aorta, and stomach. One limitation of TEE is that the left main bronchus disrupts the views of the aortic arch and proximal ascending aorta.

The 2013 Basic Perioperative Transesophageal Echocardiography Examination guidelines list the 11 most relevant views for a basic echocardiographer. These include:

1. Mid-Esophageal (ME) Four-Chamber View
2. ME 2-Chamber View
3. ME Long-Axis (LAX) View
4. ME Ascending Aortic LAX View
5. ME Ascending Aortic short-axis (SAX) View
6. ME AV SAX View
7. ME RV Inflow-Outflow View
8. ME Bicaval View
9. Transgastric (TG) Midpapillary SAX View
10. Descending Aortic SAX View
11. Descending Aortic LAX View[7]

The updated 2013 Guidelines for Performing a Comprehensive Transesophageal Echocardiographic Examination include 28 views. These include:

1. ME Five-Chamber View
2. ME Four-Chamber View
3. ME Mitral Commissural View
4. ME 2-Chamber View
5. ME LAX View
6. ME AV LAX View
7. ME Ascending Aorta LAX View
8. ME Ascending Aorta SAX View
9. ME Right Pulmonary Vein View
10. ME AV SAX View
11. ME RV Inflow-Outflow View
12. ME Modified Bicaval TV View
13. ME Bicaval View
14. ME Right and Left Pulmonary Vein View
15. ME LA Appendage View
16. TG Basal SAX View
17. TG Midpapillary SAX View
18. TG Apical SAX View
19. TG RV Basal View
20. TG RV Inflow-Outflow View
21. Deep TG Five-Chamber View
22. TG 2-Chamber View
23. TG RV Inflow View
24. TG LAX View
25. Descending Aorta SAX view
26. Descending Aorta LAX view
27. UE Aortic Arch to LAX View
28. UE Aortic Arch SAX View[6]

In addition, there are guidelines for the performance of an intraoperative 3-dimensional TEE exam.[8]

Indications

There are multiple clinical indications for TEE.  It typically provides superior imaging versus transthoracic echocardiography. It is an invasive test, however, and its use in patients should be warranted.  Indications for TEE include:

• Evaluation of acute aortic pathology (dissection, transection)
• Evaluation of prosthetic heart valves
• Evaluation of paravalvular abscess
• Evaluation of patients where TTE imaging is inadequate and the information obtained would change management
• All open heart valvular and thoracic aortic surgical procedures
• Coronary artery bypass surgeries (CABG): Its use should be considered to confirm the preoperative diagnosis, detect new pathology, to adjust the surgical plan, or to assess surgical intervention
• Catheter-based cardiac procedures (i.e., TAVR, left atrial appendage device implantation, or atrial septal defect closure)
• Non-cardiac surgery where known or suspected cardiovascular disease may result in hemodynamic compromise
• The unexplained life-threatening circulatory instability that is not corrected by usual therapy (rescue TEE)
• Diagnosis of suspected pulmonary embolism
• Confirmation and diagnosis of air embolism, particularly in neurosurgical procedures
• Evaluation of pericardial effusion
• Evaluation of congenital cardiac disease in the intraoperative period[6][9]

Contraindications

Transesophageal echocardiography (TEE) is considered to be a relatively safe procedure when performed by a trained physician. There is disagreement in the literature and among experts in the field about the presence of absolute and relative contraindications to the use of transesophageal echocardiography. However, many practitioners agree that the following conditions are

Absolute

• Perforated viscous
• Esophageal pathology including stricture, trauma, tumor, scleroderma, Mallory-Weiss tear, diverticulum
• Active upper gastrointestinal bleeding
• Recent upper gastrointestinal surgery
• Previous esophagectomy or esophagogastrectomy
• Unrepaired tracheoesophageal fistula
• Poor airway control
• Severe respiratory depression
• Uncooperative, unsedated patient

Relative

• Atlantoaxial joint disease
• Severe cervical arthritis
• Prior radiation to the chest
• Symptomatic hiatal hernia
• Recent upper gastrointestinal bleed
• Presence of esophagitis or peptic ulcer disease
• Thoracoabdominal aneurysm
• Barrett's esophagus
• History of dysphagia
• Coagulopathy or thrombocytopenia
• History of esophageal or gastric surgery
• History of esophageal cancer Esophageal varices or diverticulum
• Vascular ring, aortic arch anomaly with or without airway compromise
• Oropharyngeal pathology
• Post-gastrostomy or fundoplication limit imaging to esophageal windows

According to the 2010 American Society of Anesthesiologists and Society of Cardiovascular Anesthesiologists Practice Guidelines for Perioperative Transesophageal Echocardiography, TEE may be utilized in patients with oral, esophageal, or gastric conditions if the expected benefit is greater than the potential risk and if the necessary precautions are followed. These include limiting the exam or its duration, the avoidance of unnecessary probe manipulations, having the exam performed by the most experienced echocardiographer, acquiring a gastroenterology consult, and the consideration of other imaging options such as TTE or epicardial echocardiography.[6][9]

Equipment

Knowledge and understanding of ultrasound physics and familiarity with the echocardiography machine and its controls are paramount to obtain useful TEE imaging, decrease artifacts, and to prevent misdiagnosis. Equipment required for a transesophageal echocardiography exam includes both an echocardiography machine and an appropriate transducer, as well as a method to archive and store, completed examinations.  The multiplane (meaning that its imaging angle can be adjusted from zero to one-hundred eighty degrees) TEE probe has a connector that can be attached to the ultrasound machine, 2 dials that control side-to-side and forward and backward movement of the tip, and an ultrasonic transducer at the end. The transducer contains ceramic lead zirconate titanate and consists of a phased array of piezoelectric crystals which both send and receive ultrasound waves. The transducer and probe may be 2-dimensional or 3-dimensional and contain a dramatically increased number of crystals. During an exam, the transducer will lie in contact with the esophagus or stomach and generate sound waves which will be attenuated, refracted, scattered, or reflected back from certain cardiac structures. In echocardiography, ultrasound with frequencies of 2 to 10 MHz is utilized. This is significantly higher than sound in the audible range (the upper limit of which is approximately 20,000 Hz). The piezoelectric crystals will then convert the reflected sound into electric pulses which allow the creation of an image of the heart or other structure on display.[6][10]

One end of the TEE probe is a connector that is plugged and locked into the echocardiography machine. The handle of the probe has two control wheels and image array rotation buttons. The wheels control the side-to-side and front-to-back movement of the articulating end of the probe. The handle also contains a lock which allows the user to lock the probe in a certain configuration that is initially set by the control wheels.  In addition to the movement controlled by the wheels, the probe can be inserted or withdrawn and can be twisted to the left or right. The buttons allow the piezoelectric crystals to be rotated clockwise or counterclockwise from zero to one-hundred eighty degrees. Adult TEE probes are very similar but larger than a standard gastroscope. Pediatric TEE probes are a considerably smaller diameter, higher frequency, and have more flexibility in the shaft.[11]

The keyboard and control panel of the echocardiography machine contains a plethora of options for adjustment and acquisition of the probe, display, and acquisition of the image. Some of these include a system gain setting, time gain compensation, compression, image depth and width, B-mode, color Doppler, pulse wave Doppler, continuous wave Doppler, power output, image freeze, and image store or acquire.[6]

Personnel

Although transesophageal echocardiography is a relatively safe modality, it is an invasive procedure and does carry the risk of infrequent but potentially life-threatening complications. Therefore, it should only be performed by qualified, trained physicians. There are multiple, recently published guidelines that cover the training and maintenance of certification guidelines for the practice of intraoperative echocardiography. Cardiologists often have a base of knowledge in transthoracic echocardiography before learning transesophageal echocardiography. This is not always the case for anesthesiologists, who utilize intraoperative TEE at a much higher rate than TTE. The majority of the intraoperative echocardiography guidelines are synthesized and published by the American Society of Anesthesiologists (ASA), the Society for Cardiovascular Anesthesiologists (SCA), and the American Society of Echocardiography (ASE). Physicians typically demonstrate their competence in echocardiography by completion of a training program and achieving a passing score on a certifying exam. The primary examination and certification organization for intraoperative echocardiography is the National Board of Echocardiography (NBE) which was founded in 1998 by a joint partnership between the SCA and the ASE.[6]

The NBE offers examinations and certifications in the following areas: 

• The ASCeXAM is for physicians who can show special competence in all areas of echocardiography including TTE, TEE, and stress echocardiography - this exam and certification is most commonly taken and acquired by cardiologists
• The Advanced PTEeXAM is intended for physicians who are especially competent in advanced perioperative transesophageal echocardiography - this is the exam and certification which is most commonly acquired by cardiovascular anesthesiologists; the goal of this exam is to demonstrate the full diagnostic and surgical decision-making capacity of perioperative TEE
• The Basic PTEeXAM covers basic perioperative transesophageal echocardiography: The goal of this exam and certification is the process of intraoperative non-diagnostic monitoring except in the case of an emergent situation; this exam and certification is most commonly obtained by general anesthesiologists and is not specifically designed for those who routinely practice cardiovascular anesthesiology

In order to acquire certification in any of the above areas, the physician applicant must not only pass a computerized exam, he or she must also complete a variety of additional requirements including personally performing a certain number of applicable echocardiography examinations, completion of a certified training program, acquisition of a certain number of continuing medical education requirements, and the achievement of board certification in their specialty.[6][12]

Preparation

Detailed history and physical examination should be done prior to the procedure to rule out contraindications for the procedure. Patient should be thoroughly assessed for suitability for moderate sedation. The history and physical examination should focus on identifying risk factors that may increase susceptibility to sedatives and analgesics, such as cardiopulmonary diseases, renal and hepatic impairment that can slow down drug metabolism, history of allergic reactions or problems with airway in the past during anesthesia, snoring or sleep apnea.

Technique or Treatment

After pre procedure clearance, probe is inserted via mouth under moderate sedation. Patient's vitals should be monitored continuously during the procedure. The probe is inserted and is manipulated to obtain different views of the heart. The following terminology is used in the ASE/SCA guidelines to understand the manipulation of the probe with the assumption that the imaging plane is anterior to the esophagus looking into the heart in a patient in supine anatomic position.[6]

Rotating the anterior aspect of the probe within the esophagus clockwise is called “turning to the right” and rotating it counterclockwise is called “turning to the left”. “Advancing the transducer” means pushing the tip of the probe more distal into the esophagus or the stomach while pulling the tip more proximally is called “withdrawing the probe”.  Flexing the tip of the probe with the large control wheel anteriorly is called “anteflexing”, and flexing it posteriorly “retroflexing”.  Using the small control wheel, flexing the tip of the probe to the patient's right is called “flexing to the right”, and flexing it to the left is called “flexing to the left”. Finally, increasing the transducer multiplane angle from zero degrees towards 180 degrees is called “rotating or multiplane forward”, and decreasing in the opposite direction towards zero degrees is called “rotating or multiplane back”.

Complications

Although transesophageal echocardiography (TEE) has the reputation of a safe imaging modality, it does carry the risk of complications that range from mild to potentially life-threatening. The physical insertion and manipulation of the TEE probe in the intraoperative setting can cause a variety of gastric, esophageal, and oropharyngeal complications. According to several large studies, the overall rate of TEE related complications ranged from 0.2% to 1.4%. Intraoperative TEE does carry slightly different risks in comparison to TEEs performed in the ambulatory setting because patient's that undergo TEE in the operating room (OR) are typically under general anesthesia and have received neuromuscular blocking agents. These patients are unable to swallow and potentially protest dangerous probe manipulations. In addition, the TEE probe is often kept inserted for a prolonged period in the operating room, particularly in patients undergoing cardiac surgery. Despite these challenges, the rate of TEE related compilations appears to be similar in the ambulatory and operating room settings. Many of the gastrointestinal injuries related to TEE may not present until after the first twenty-four hours and may have previously led experts to underestimate the overall risk of TEE related complications.

TEE related injuries include:

• Laceration of lip
• Loose or chipped tooth
• Tongue ulceration                                           
• Laceration of the oropharynx
• Dysphagia
• Odynophagia
• Pharyngeal edema
• Vocal cord palsy or paralysis
• Gastritis
• Stomach ulceration
• Esophagitis
• Esophageal perforation
• Mallory-Weiss tear
• Dysrhythmias
• Compression of the mediastinal structures
• Inadvertent extubation[6][13][9]

Clinical Significance

In summary, transesophageal echocardiography has seen a dramatic increase in usage over the past decade, from cardiac surgery to its use as a monitoring or rescue device in high-risk patients undergoing non-cardiac surgery.  The widespread availability of echocardiography machines and the increased number of physicians with training in their use has led to this increased usage. 

The clinical benefits of intraoperative TEE are of two types, those that impact hemodynamic/airway management and those that result in changes in the surgical procedure. Multiple groups have reported that intraoperative TEE for both cardiac and non-cardiac surgery detects unrecognized conditions such as hypovolemia, wall motion abnormalities and right ventricular failure. In these cases, use of TEE helps guide appropriate administration of volume, vasopressors, inotropes and inodilators. TEE has also resulted in changes in surgical procedures. It is often used to assess quality of valve repair or replacement and, if judged to be inadequate, the patient will be placed back on cardiopulmonary bypass for revision or conversion from perhaps valve repair to valve replacement. TEE has also demonstrated deterioration of wall motion post-cardiopulmonary bypass, indicating air that needs to be vented from a bypass graft, or a more serious problem that requires further surgical revision of a graft. Mild desaturation may be explained by detection of a patent foramen ovale, which can be managed by appropriate adjustment of systemic vascular resistance. A previously unrecognized large patent foramen ovale, atrial or ventricular septal defect, or clot in the left atrial appendage, have all resulted in modification of the surgical plan. Finally, severe hemodynamic instability has sometimes been explained by visualization of thrombi in the right side of the heart or pulmonary artery. In other cases, thrombi have not been visualized, but signs of right-sided heart failure, consistent with pulmonary embolism, have led to further studies that confirmed the presence of pulmonary emboli. Treatment of such patients has included thrombolysis and, when appropriate, surgical embolectomy.

There is strong evidence to support the use of TEE in non-cardiac surgery both for monitoring and as a diagnostic rescue device when unexplained life-threatening circulatory instability persists despite attempts at correction.  In addition, TEE is frequently used in surgical procedures where the patient has severe cardiovascular comorbidities which may lead to significant hemodynamic, pulmonary, or neurologic instability during the case.[14][15]

With the increased attention given to ultrasound education during medical training and the increased availability of echocardiographic equipment, the use of echocardiography will most certainly increase in the future.[4]

Enhancing Healthcare Team Outcomes

Although transesophageal echocardiography is a relatively safe modality, it is an invasive procedure and does carry the risk of infrequent but potentially life-threatening complications. Therefore, it should only be performed by qualified, trained physicians. Cardiologists, anesthesiologists and critical care physicians who demonstrate their competence in echocardiography by completion of a training program and achieving a passing score on a certifying exam, can safely perform the procedure. Improving health professional understanding of how to utilize TEE to evaluate and treat patients can lead to better patient outcomes.