Although transesophageal ultrasound was first reported in the 1970s, the advent of phased array transducers and flexible transesophageal probes in the early 1980s enabled improved visualization of cardiac structures. Transesophageal echocardiography has become a commonly used imaging modality in a wide range of settings including the cardiac operating theatre, the intensive care unit, the interventional laboratory, as an outpatient procedure, and as a monitoring or rescue device in patients who have or are expected to have unexplained cardiovascular instability. TEE is able to provide excellent ultrasonic imaging compared to transthoracic echocardiography (TTE) because of the proximal location of the esophagus next to the heart and great vessels. In addition, TEE is more practical than TTE during most surgeries and especially during cardiac surgical operations because of the operating field. For these reasons, TEE is superior to TEE during cardiac surgery, for certain diagnosis, and for many catheter-based cardiovascular interventions. Recently, the development and widespread availability of real-time 3-dimensional echocardiography has expanded the role of TEE in the guidance of complicated cardiac surgical procedures and catheter-based cardiac interventions such as transcatheter aortic valve replacements (TAVR).
The Society of Cardiovascular Anesthesiologists (SCA) and the American Society of Echocardiography (ASE) published a first set of guidelines for the performance of a comprehensive intraoperative TEE exam in 1999. The aim of these guidelines was to define a standard examination for the purposes of training, consistency, storage, and quality. These guidelines contain a set of twenty TEE views that were primarily designed for intraoperative use although they have been widely adopted outside of the operating room. These guidelines were updated in 2013 to now include an expanded 28 standard views as well as 3-dimensional imaging. In addition, a set of basic perioperative TEE guidelines were also published in 2013 that included 11 standard views. The SCA and the ASE realized that the availability and use of TEE as a monitoring and diagnostic rescue tool outside of cardiac surgery had dramatically increased. Therefore, a basic set of guidelines that were intended for use in general operating rooms by non-cardiac anesthesiologists were developed.
Many practicing physicians that utilize TEE become certified in its use by the National Board of Echocardiography. This requires passing a test and the completion of several other requirements including a certain number of personally performed TEE exams.
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:
The updated 2013 Guidelines for Performing a Comprehensive Transesophageal Echocardiographic Examination include 28 views. These include:
In addition, there are guidelines for the performance of an intraoperative 3-dimensional TEE exam.
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:
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 contraindications: perforated viscous, esophageal pathology including stricture, trauma, tumor, scleroderma, Mallory-Weiss tear, diverticulum, active upper gastrointestinal bleeding, recent upper gastrointestinal surgery, and previous esophagectomy or esophagogastrectomy. Relative contraindications to the use of transesophageal echocardiography include, but are not limited to, atlantoaxial joint disease, severe cervical arthritis, prior radiation to the chest, symptomatic hiatal hernia, history of gastrointestinal surgery, recent upper gastrointestinal bleed, the presence of esophagitis or peptic ulcer disease, thoracoabdominal aneurysm, Barrett's esophagus, history of dysphagia, and coagulopathy or thrombocytopenia. 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.
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 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.
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.
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.
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 TTE 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.
The NBE offers examinations and certifications in the following areas:
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.
Transesophageal echocardiography (TEE) probes placed intraoperatively are usually placed while the patient is under general anesthesia. Less commonly, the probe may be placed under conscious sedation. Before placement, the probe is typically lubricated with a water-soluble jelly, and a bite block is placed. TEE probes are frequently passed into the esophagus in a similar manner to which an orogastric tube is placed. If the patient is under general anesthesia, the jaw may be lifted with the non-dominant hand and the probe inserted with the dominant hand with the probe slightly anteflexed. The TEE probe is typically inserted with continuous gentle pressure while carefully maneuvering the probe to the left or right to engage the esophageal opening. Resistance to probe advancement may occur because of overextension of the neck or if the probe is off to one side or the other. When the probe crosses the larynx and the cricopharyngeus muscle, a noticeable loss of resistance will be appreciated, and the probe will be located in the upper esophagus. If there is difficulty placing the probe with the above maneuvers, a laryngoscope may be utilized to displace the mandible and assist in placement anteriorly.
If the exam is to be performed under sedation, several additional steps are required before probe placement. Topical anesthetics such as Benzocaine spray or viscous lidocaine are frequently utilized to anesthetize the oropharynx before sedation. Short-acting benzodiazepines such as Midazolam and opioids such as fentanyl are frequently used as sedation for TEE exams. Their quick onset and short duration of action make them ideal for this purpose. Propofol is an ideal sedation agent for this procedure, but its high risk of apneic events and need for airway intervention makes it better suited for use by anesthesiologists and other anesthesia providers. After topicalization, a bite block is placed in the patient's mouth, and the probe is lubricated. Sedation agents are given, and the probe is inserted into the pharynx with mild anteflexion of the probe. The patient will be asked to swallow, and the probe is advanced into the esophagus in a neutral position to avoid adjacent structures such as the piriform fossa. Certain patients will not be able to tolerate mild sedation and require deep sedation or general anesthesia for TEE probe placement and exam. These patients may require anesthesiology involvement.
After the probe reaches the esophagus, it may be inserted more deeply into the esophagus and stomach or pulled back out to obtain the necessary images. Also, the wheels on the handle of the probe may be used to anteflex/retroflex or move the probe tip to the left or right.
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:
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 often indirect. In other words, they usually result from changes in surgical management as a result of findings on the echocardiographic exam. Many centers or hospitals utilize TEE in every cardiac surgical case despite the lack of proven direct benefit.
There is strong evidence to support the use of TEE in non-cardiac surgery 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.
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.