Transesophageal echocardiography (TEE) presents a unique opportunity to overcome the limitations posed by chest wall acoustic windows while allowing visualization of cardiac structures with greater spatial resolution. Since its first reported use to evaluate intracardiac flow in 1971 and to visualize cardiac structures in 1976, the TEE probe has undergone remarkable technological advancement in terms of imaging capability and probe structure and design.^1,2 The TEE probe used by Frazin et al¹ consisted of an M-mode transducer attached to a coaxial cable. Souquet et al³ then reported successful use of a phased array transducer attached to the end of a gastroscope, which, in addition to producing two-dimensional images, allowed for finer control of the transducer position by using the flexion and angling controls akin to a gastroscope. The biplane transducer was then introduced in 1984, followed by the multiplane transducer in 1992.⁴ Consistent technological developments, including the introduction of a flexible endoscope, probe temperature regulation, miniaturization, transducer design, addition of color and spectral Doppler, and three-dimensional imaging, have led to the widespread adoption of TEE in clinical care. Currently TEE accounts for approximately 5% to 10% of echocardiographic procedures.⁵

The modern TEE probe consists of the following components (see Fig. 2-1).

Probe Tip

TEE probe tips are miniaturized (adult 3D probes: ~17 × 13.5 × 38 mm and infant/pediatric probes: ~7.5 × 5.5 × 18.5 mm) and feature smooth contours to allow safe and comfortable insertion into the oropharynx. The acoustic lens and matrix array are housed in the probe tip. Modern TEE probes typically have an extended operating frequency range of approximately 3 to 7 MHz with a 90-degree field of view and usually allow 180 degrees of electronic rotation. The probe tip can also be flexed, extended, and angled left or right using dials on the probe handle. Generally, probes are capable of flexion of up to 120 degrees, extension of 60 degrees, and 45 degrees of left/right angulation, with some variation between manufacturers. TEE probes with three-dimensional imaging capabilities allow for live, zoom, biplane, and multibeat acquisition with or without color Doppler. Three-dimensional imaging is possible by performing a significant portion of beam forming within the transducer in highly specialized integrated circuits, which enable the fitting of thousands of piezoelectric elements into the tip of the transducer (see Chapter 23).

Probe Shaft

The TEE probe shaft houses flexible, mini-coaxial cables carrying signals to and from the transducers. The probe shaft is about 6 to 10 mm in diameter and 0.7 to 1 m in length and is designed to be flexible and durable with some degree of bite resistance. The probe shaft is labeled with markers that allow assessment of the depth of esophageal intubation. The depth markers at 20 to 30 cm roughly correspond to upper esophageal views, 30 to 40 cm to mid-esophageal views, 40 to 45 cm to transgastric views, and 45 to 50 cm to deep transgastric views.

Handle

The handle of the TEE probe houses the controls needed to perform electronic steering of the imaging elements and mechanical steering of the TEE probe tip. There are typically two round dials. The larger dial allows flexion and extension movements of the probe tip, and the smaller dial allows for right and left movements of the probe tip. In addition, the handle houses two button controls that help with electronic steering. Ultrasound equipment manufacturers try to optimize the ergonomics of the handle to permit for an easy one-handed operation. Design feature improvements such as the introduction of a slim, lightweight handle, textured no-slip grip, and accessibility of controls have made it more user friendly.

Connector

The connector contains an array of pins, which attach to the echo machine (see Fig. 2-2). It is connected to the probe handle via the transducer cable. Typically, the echo system will run an automatic calibration algorithm when the probe is first connected with the echo machine. It is generally recommended that the probe tip position be neutral when this connection is made.

Indications for TEE

Before assessing whether a patient is a suitable candidate for a TEE, it is prudent to first determine the appropriateness of the indication for the study. General indications for TEE include assessment of left-atrial appendage thrombus, atrial masses, detailed inspection of valvular pathology, and diagnosis of endocarditis or cardioembolic source. More recently, TEE has been used to provide anatomical guidance for percutaneous valve procedures, such as the MitraClip procedure.⁶ In 2011 a multisociety joint guideline was published for the appropriate use of echocardiography, including TEE.⁷ Indications for the study were scored on a scale of 1 to 9, and indications with a score of 7 to 9 were considered appropriate (A = benefit outweighed risk), whereas those with a score of 4 to 6 were considered uncertain (U), and those with a score of 1 to 3 were considered inappropriate (I = risk outweighed benefit). Table 2-1 shows the appropriateness score for indications commonly encountered in clinical practice. Practice guidelines for the use of perioperative TEE⁸ recommend that for adult patients without contraindications, TEE should be used in all open heart (e.g., valvular procedures) and thoracic aortic surgical procedures, and should be considered in coronary artery bypass graft surgeries as well “in order to confirm and refine the preoperative diagnosis, to detect new or unsuspected pathology, to adjust the anesthetic and surgical plan accordingly, and to assess the results of the surgical intervention.”

In recent years, TEE in the perioperative period has been invaluable in guiding percutaneous valve procedures such as placement of the transcatheter aortic valve and mitral clip. Indeed, the first setting in which perioperative TEE was widely adopted and routinely employed was the cardiac surgical operating room. In a large prospective cohort study, Mishra and colleagues found that 36% of 5016 cardiac surgical patients benefited from a pre-bypass TEE study and a similar number from a post-bypass study.⁹ The TEE examination was most useful for identification of intracardiac thrombus, aortic atheroma, mitral leaflet configuration, changes in valvular function, and in guiding de-airing procedures before separation from bypass.

In some centers, TEE has replaced transthoracic echocardiography (TTE) as the preferred initial imaging study in postcardiac surgery patients requiring emergent evaluation. This is because of its ability to obtain superior-quality images, whereas TTE imaging is often limited by sound attenuation from air through the chest wall acoustic windows. In one study the average time to reach a diagnosis by TEE was 11 minutes, and the etiology of refractory hypotension was clearly identified in 76% of patients.¹⁰ As more anesthesiologists have become skilled in the performance and interpretation of TEE, its use during noncardiac surgery has increased. In a cohort of 98 patients with high cardiac risk undergoing a broad range of noncardiac surgery, Schulmeyer and colleagues found that TEE helped guide intraoperative and/or postoperative management in all but 2 patients.¹¹ Suriani and coworkers reported their use of TEE in 123 cases of orthotopic liver transplant.¹² In 15% of cases, TEE was critical in altering surgical or anesthetic technique, treating life-threatening events, or directing further postoperative evaluation. In this population, TEE also can be useful in diagnosing hepatopulmonary syndrome by identifying bubbles in the pulmonary veins after a bubble test.

TEE is of proven value in evaluating hemodynamically unstable patients. Feierman¹³ reported the use of intraoperative TEE to identify unsuspected dynamic left ventricular outflow tract obstruction, thereby allowing crucial redirection of management strategy. In addition, Brandt and associates reviewed 66 cases in which intraoperative TEE was emergently applied to diagnose severe left ventricular dysfunction, aortic dissection, new myocardial wall motion abnormalities, patent foramen ovale, localized cardiac tamponade, and right ventricular dilatation consistent with a pulmonary embolism.¹⁴ TEE is commonly used in critical care units. Among 308 TEE studies conducted in an intensive care unit in Australia, the most common indications were refractory or unexplained hypotension (67%), suspected endocarditis (27%), evaluation of ventricular function (15%), evaluation of pulmonary edema of uncertain etiology (6%), evaluation of the aorta (4%), and search for a source of systemic embolus (4%). Twenty-five percent of these examinations were requested after an inadequate TTE examination. The subsequent TEE examination led to changes in therapy in 32% of patients studied and to immediate surgery in 22%, with the greatest yield in postcardiac surgery patients.¹⁵ Others have reported using TEE in ICUs to guide central line placement, evaluate patients with unexplained hypoxemia, or evaluate potential heart donors.^16,17

The proximity of the esophagus to the aorta allows for precise and accurate diagnosis of certain types of aortic pathology when using TEE, and this application has found a specific niche in the emergency room (ER). Minard and colleagues compared TEE with aortography to diagnose traumatic disruption of the aorta, including intimal flaps, pseudoaneurysms, dissections, and intraluminal or extraluminal hematomas, and gross dissections with identification of false and true lumens. However, the sensitivity and specificity of TEE were lower than those of aortography, most likely due to the inability of TEE to image the upper third of the ascending aorta and the aortic arch.^18,19 Even though some forms of aortic pathology are not completely assessed with TEE, this technique is very valuable in ruling out aortic dissection. Yalcin and coworkers reported TEE to be 98% sensitive and 99% specific for detection of aortic dissection, and a 2006 meta-analysis of 10 studies reported similar results (98% sensitive, 95% specific).^20,21 In addition, of significant importance is the fact that TEE is often safer than other imaging modalities in hemodynamically unstable patients, as it can be performed at the bedside. Overall, despite its known deficiencies, TEE remains the first-line test for evaluation of the aorta due to its portability, low cost, low level of invasiveness, rapidity, and low complication rate. In the presence of a negative study, however, it is often necessary to proceed to further radiological imaging if the clinical suspicion of aortic pathology remains high.^18,21–23