I. INDICATIONS.
In general, transesophageal echocardiography (TEE) is performed when there is a clinical question for which the information obtained using transthoracic echocardiography (TTE) is insufficient. This may be to better define pathology that has been identified by TTE or to obtain better images when transthoracic images are inadequate. The close proximity of the esophagus to the heart allows for improved visualization of many cardiac structures, particularly those that are posteriorly located. In addition, higher frequency probes can be used, given the shorter distance between the probe and the heart, further enhancing the resolution. However, imaging planes are somewhat constrained by the relative position of the esophagus and heart, and some structures (e.g., prosthetic aortic valve) and certain Doppler measurements may be better assessed by TTE.
Indications for TEE in various conditions and clinical situations are listed in
Table 68.1. Very common indications include examination to rule out a cardiac source of embolus, assessment of valves, prosthesis, and intracardiac device for endocarditis or its accompanying complications, such as abscess. The assessment of native and prosthetic valvular function, in terms of degree and mechanism of regurgitation or stenosis, is a frequent indication for TEE. Acoustic shadowing by prosthetic valves, particularly in the mitral position, poses less of a problem for TEE than it does for TTE. Given the increasing prevalence of atrial fibrillation, another frequent indication for TEE is to assess left atrial and left atrial appendage pathology and function, particularly prior to cardioversion. Congenital cardiovascular abnormalities, intracardiac shunts, as well as intracardiac tumors and masses can also be well delineated by TEE. Because of its ability to assess the ascending aorta, arch, and descending aorta, TEE also has an important role in the diagnosis of aortic dissection, aneurysms, and atheroma. In extremely technically difficult/limited transthoracic study such as in postoperative and mechanically ventilated patients, TEE may be used for usual TTE indications such as the assessment of left ventricular function.
TEE is a useful imaging modality in both the operating room and the cardiac catheterization laboratory. In cardiothoracic surgery, TEE is used to assess the mechanism of valvular abnormalities and subsequently evaluate the efficacy of valve repair or replacement. TEE can be used to guide the location of the aortic cross-clamp so that segments with severe atheromatous involvement can be avoided, thereby reducing the risk of embolization. In addition, TEE can provide an assessment of left ventricular function and regional wall motion. As newer transcatheter approaches have become common, including percutaneous valve procedures, closure of paraprosthetic leaks, atrial septal defects, ventricular septal defects, and patent foramen ovale as well as electrophysiological procedures, TEE has been increasingly utilized to help guide catheter position and placement of percutaneous valve or occluding device and evaluate the success and complications of the procedure.
II. CONTRAINDICATIONS
A. There are few
absolute contraindications to the performance of TEE (
Table 68.2). These include the
presence of pharyngeal or esophageal obstruction, active upper gastrointestinal bleeding, recent esophageal or gastric surgery, and suspected or known perforated viscus. If there is instability of the cervical vertebrae, then the examination cannot be performed.
B. Relative contraindications include the presence of esophageal varices and sus pected esophageal diverticulum. In these cases, it is prudent to obtain gastrointes tinal evaluation before proceeding, if the study must be performed. Severe cervical arthritis, in which patients may have difficulty with neck flexion, may make it dif ficult to pass the probe. Oropharyngeal pathology, anatomic distortion, or extreme muscle weakness can likewise make it difficult to proceed with the examination.
C. Severe cardiopulmonary disease is not a contraindication to evaluation by TEE (on the contrary, TEE can often provide critical information when used in these patients), but the operator must be particularly careful to minimize any stress on the patient. This is particularly true in suspected aortic dissection, where any sudden increase in blood pressure caused by patient discomfort could result in extension of the dissection. In cases where there is respiratory instability, endotracheal intubation with assisted ventilation should be considered prior to the procedure. Patients who are hypotensive may not be able to receive sedative agents, as these agents could lead to further hemo dynamic compromise. In such patients, the examination may have to be performed with topical anesthesia alone. This is obviously much more difficult for the patient, and TEE should be done only if critical information is not obtainable by other methods.
D. Given the invasive nature of the procedure, prudence must be observed in patients who are prone to bleeding. The procedure is commonly performed on patients who are anticoagulated, such as in those with atrial arrhythmias prior to cardioversion. However, there is increased risk in those who are overanticoagulated. Although no set guidelines exist, it would seem advisable to delay the examination if possible in patients with an international normalized ratio > 5 or a partial thromboplastin time > 100 sec onds. Thrombocytopenia may also increase the risk, particularly with platelet counts < 50,000/mm3. TEE can still be performed if needed, as the absolute risk remains low, but meticulous attention must be given to nontraumatic esophageal intubation.
E. Esophageal infections, such as those that occur in the context of human immunode ficiency virus (HIV), do not necessarily represent contraindications to the procedure. Patient discomfort caused by the presence of the probe in the esophagus may pre clude the examination. Universal precautions should be followed (as they should for any patient). The standard disinfectants used to clean the probe will inactivate HIV.
F. A patient who is very uncooperative is at significant risk for complications from the procedure. In such a case, consideration should be given to aborting the TEE or to increase the level of sedation and prophylactic endotracheal intubation if required.
III. PERSONNEL.
The American Society of Echocardiography has proposed the following guidelines for operators who wish to perform TEE: as background, attainment of at least level 2 experience in transthoracic echocardiogram; a minimum of 25 esophageal intubations under guidance; and a minimum of 50 supervised TEE examinations during training. Furthermore, operators should perform a minimum of 25 to 50 TEE examina tions yearly to maintain competency.
The presence of a skilled assistant is invaluable during the procedure. The assistant should be either a sonographer or a registered nurse. The role of the assistant is to monitor vital signs during the procedure, ensure proper suctioning of oropharyngeal secretions, and administer medications.
