From the *Department of Anesthesiology, University of Nebraska Medical Center, Omaha, Nebraska; and †Department of Anesthesiology, Vanderbilt University, Nashville, Tennessee.
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INDEX CASEA 62-year-old man recovered for 1 hour in the post-anesthesia care unit following a colectomy. He became acutely hypotensive and hypoxic and did not respond to initial fluid bolus or epinephrine. He has a history of esophageal strictures and dysphagia, precluding the use of transesophageal echocardiography (TEE). A transthoracic echocardiogram (TTE) was performed to evaluate the cause of his hemodynamic instability.DISCUSSIONTTE and TEE are 2 common perioperative cardiac imaging modalities. Understanding the similarities, differences, and benefits of TTE and TEE is useful for the perioperative echocardiographer. Familiarity with TTE views provides an excellent knowledge base for recognition of the related TEE views. For instance, anatomical structures present in the TTE apical 4-chamber view are easily recognized in the TEE midesophageal 4-chamber view.TTE and TEE are complementary in their ability to provide better resolution of specific structures. TTE offers superior resolution of the anterior structures, such as the right ventricle, right ventricular outflow tract, pulmonic valve, and anterior pericardium. TTE apical views provide superior imaging of the pericardium and left ventricular apex. Imaging of the posterior structures, such as the left atrium, mitral valve and subvalvular apparatus, interatrial septum and left atrial appendage, is best achieved with TEE. The following paragraphs will compare 5 of the basic TTE views and their corresponding TEE views, and identify their advantages and disadvantages. A discussion of proximal aortic imaging with TTE and TEE is also included.IMAGING MODALITIESTransesophageal EchocardiographyThe TEE probe is a flexible ultrasound gastroscope that is advanced along the esophagus and into the stomach to image the heart and great vessels. Because of the close proximity to the heart, TEE requires less depth penetration and uses higher frequency transducers (5–7 MHz) enabling superior spatial resolution of the posterior cardiac structures when compared with TTE. TEE remains the imaging modality of choice for intraoperative cardiovascular assessment, especially during cardiac surgery.1,2Transthoracic EchocardiographyTTE uses lower frequency (3-5 MHz) ultrasound to allow greater depth penetration at the expense of spatial resolution. The TTE transducer is placed directly on the patient’s chest in 4 windows: parasternal, apical, subcostal, and suprasternal. In contrast to TEE, TTE images anatomic structures from anterior to posterior.Chamber quantification is more readily accomplished by TTE, where the distance between the probe allows for complete capture of the ventricular and atrial borders.6 TTE can be performed rapidly, noninvasively, and provide accurate hemodynamic assessments during cardiovascular emergencies such as cardiac tamponade and circulatory shock.4,5 TTE generally provides more reliable hemodynamic data as it affords more flexibility of transducer position. However, TTE may be limited by factors such as supine patient positioning, inability to access the chest without contaminating the surgical field, and presence of mediastinal tubes. Mediastinal air, tubes, and surgical dressings can impede ultrasound transmission and limit the utility of TTE imaging.COMPARABLE TTE AND TEE VIEWSIn Table 1, 5 basic TTE views along with corresponding TEE views are listed with the structures that are imaged.TTE and TEE Left Ventricle Long-Axis ViewsIn TTE, the parasternal long-axis view is obtained by placing the probe at the 3rd and 4th intercostal space directly left of the sternum with the index mark pointing toward the right shoulder as demonstrated in composite Video 1 (see Supplemental Digital Content 1, http://links.lww.com/AA/A528).