Epicardial Echocardiography and Epiaortic Ultrasonography

Epicardial Echocardiography and Epiaortic Ultrasonography 20 Stanton K. Shernan and Kathryn E. Glas Despite its overwhelming popularity and favorable influence on perioperative clinical decision making and outcome, the transesophageal echocardiographic (TEE) approach to a comprehensive echocardiographic examination may be limited by impaired imaging of the distal ascending aorta and aortic arch, difficulty in advancing the probe within the esophagus in some patients, and contraindications for probe placement in those with gastroesophageal pathology. Furthermore, TEE may be rarely associated with perioperative morbidity from oropharyngeal and gastroesophageal injury. 1,2 In recognition of these potential limitations, the Society of Cardiovascular Anesthesiologists (SCA), American Society of Anesthesiologists (ASA), and American Society of Echocardiography (ASE) currently recommend that advanced intraoperative ultrasonographers also become familiar with epicardial echocardiography and epiaortic ultrasound in addition to TEE. 3,4 The ASE and SCA have subsequently published guidelines specifically focused on acquisition techniques and indications for both epicardial echocardiography and epiaortic ultrasonography. 5,6 Thus, while TEE remains the most frequently used intraoperative tool for imaging cardiac and intrathoracic vascular structures, it is imperative for an experienced intraoperative ultrasonogapher to also be familiar with other imaging modalities including epicardial echocardiographic and epiaortic ultrasound techniques in order to conduct a comprehensive perioperative echocardiographic examination. EPICARDIAL AND EPIAORTIC PROBE PREPARATION Epicardial and epiaortic imaging are performed by placing the ultrasound transducer on the surface of the heart or aorta, respectively, to acquire two-dimensional (2D), and color-flow and spectral Doppler images in multiple planes. Due to the proximity of the probe to the heart, these techniques typically use higher frequency probes (5 to 12 MHz). Epicardial and epiaortic imaging require adherence to strict sterile technique while manipulating the probe within the operative field. Consequently, these images may only be obtained by an operator who is wearing a sterile gown and gloves. The probe is placed in a sterile sheath along with sterile acoustic gel or saline in order to optimize acoustic transmission. Warm sterile saline can be poured into the mediastinal cavity to further enhance acoustic transmission from the probe to the cardiac or aortic surface. Additional manipulation of depth, transmit focus, gain, and transducer frequency may be required to optimize the image. EPICARDIAL ECHOCARDIOGRAPHY IMAGING PLANES The ASESCA guidelines currently recommend that the following seven epicardial echocardiographic imaging planes be obtained to perform a comprehensive 2D and Doppler echocardiographic evaluation. 5 However, the guidelines also recognize that individual patient characteristics, anatomic variations, or time constraints may limit the ability to obtain every component of the recommended comprehensive epicardial echocardiographic examination. Furthermore, modification of the recommended views may be required to obtain a more detailed interrogation of specific anatomy or pathology. Epicardial Aortic Valve Short-Axis View The ultrasound transducer is placed on the aortic root above the aortic valve (AV) annulus, with the ultrasound beam directed towards the AV in a short-axis (SAX) orientation to obtain the epicardial AV SAX view (Figure 20 1). Appropriate transducer alignment requires up to 30 of clockwise rotation with the orientation marker (indentation) on the transducer directed toward the patient s left. Epicardial Aortic Valve Long-Axis View The epicardial aortic valve long-axis (LAX) view is obtained from the epicardial AV SAX view by positioning the probe

Page 455 EPICARDIAL ECHOCARDIOGRAPHY AND EPIAORTIC ULTRASONOGRAPHY 455 Epicardial Left Ventricle Basal SAX View FIGURE 20 1. Epicardial aortic valve short-axis view. When the orientation marker (indentation) on the transducer is pointed towards the patient s left, the right coronary cusp (R) will be at the top of the monitor screen, the left coronary cusp (L) is on the bottom left, and the noncoronary cusp (N) is on the right side of the screen adjacent to the interatrial septum. upward along the right-side surface of the aortic root with the orientation marker slightly rotated clockwise and directed toward the patient s left. The ultrasound beam is directed posteriorly to visualize the left ventricular outflow tract (LVOT) and AV (Figure 20 2). The epicardial left ventricular (LV) basal SAX view is obtained from the epicardial AV SAX position by moving the probe towards the apex along the right ventricle (RV) with the transducer orientation marker again directed towards the patient s left (Figure 20 3). In this view, the RV is on top in the near field, while the LV is below in the far field of the ultrasound beam sector. The mitral valve (MV) is visualized including both leaflets forming the classic fish mouth appearance, with the anterior leaflet on the top of the screen and the posterior leaflet underneath. The anterolateral commissure lies on the right, and the posteromedial commissure on the left of the screen. Epicardial Left Ventricle Mid SAX View Angulating the probe inferiorly and to the left from the epicardial LV basal SAX view in an apical direction along the RV myocardial surface allows visualization of the RV and LV in SAX at the level of the papillary muscles (Figure 20 4). When the transducer orientation marker faces the patient s left, the anterolateral papillary muscle will be on the right side of the display and the posteriomedial papillary muscle will be on the left side. The septal wall of the LV is displayed on the left followed by the anterior, lateral, and inferior walls, respectively, in a clockwise rotation. The RV can be evaluated FIGURE 20 2. Epicardial aortic valve long-axis view. This view is optimal for measuring left ventricular outflow tract (LVOT), aortic annulus, and sinotubular junction diameters. Long-axis orientation permits continuous-wave and pulsed-wave Doppler ultrasound beam assessment of pressure gradients across the aortic valve (AV) and LVOT. Similarly, color-flow Doppler interrogation of the AV can be utilized to grade the degree of aortic insufficiency. (AO, proximal ascending aorta.) AO AV LVOT

456 Page 456 CHAPTER 20 FIGURE 20 3. Epicardial left ventricle basal short-axis view. The epicardial left ventricle (LV) basal short-axis (SAX) view can be used to evaluate the mitral valve annulus and both anterior (AL) and posterior (PL) leaflets. Color-flow Doppler can also be used to determine the origin of mitral regurgitation jets and obtain an estimate of the regurgitant orifice area. Finally, basal LV regional wall motion can be assessed utilizing the same LV wall orientation as seen in the epicardial left ventricle mid SAX. (ALC, anterolateral commissure; PMC, posteromedial commissure; RV, right ventricle.) FIGURE 20 4. Epicardial left ventricle mid short-axis view.this view is optimal for evaluating left ventricle (LV) and right ventricle (RV) global and regional function. (S, interventricular septum; A, LV anterior wall; L, LV lateral wall; I, LV inferior wall.)

Page 457 EPICARDIAL ECHOCARDIOGRAPHY AND EPIAORTIC ULTRASONOGRAPHY 457 FIGURE 20 5. Epicardial left ventricle long-axis view. This view allows visualization of the inferolateral (far field) and anteroseptal (near field) walls of the left ventricle (LV) as well as the right ventricle (RV), left atrium (LA), left ventricular outflow tract, aortic valve (AV), and mitral valve (MV). Rightward orientation of the beam allows evaluation of the right atrium and tricuspid valve. This view is also useful for diagnosing and quantifying aortic, mitral, and tricuspid regurgitation. similarly by moving the transducer further towards the patient s right. Epicardial Left Ventricle Long-Axis view From the epicardial LV mid SAX view, the ultrasound beam can be angled superiorly and rotated towards the patient s right shoulder to generate the epicardial LV LAX view (Figure 20 5). Epicardial Two-Chamber View From the epicardial LV LAX view, movement of the probe toward the anterior surface of the LV and further FIGURE 20 6. Epicardial two-chamber view.this view can be used to evaluate left atrial (LA) size and pathology, as well as mitral valve (MV) anatomy and leaflet motion. Regional wall motion of the basal and mid segments of the anterior (near field) and inferior (far field) left ventricular (LV) walls can also be obtained. clockwise rotation will develop the epicardial twochamber view, permitting evaluation of the LA, left atrial appendage, MV, and LV (Figure 20 6). Basilar and mid segments of the anterior and inferior walls of the LV can be assessed in this view. Epicardial Right Ventricular Outflow Tract View The epicardial right ventricular outflow tract (RVOT) view is developed by moving the transducer over the RVOT and directing the ultrasound beam towards the patient s left shoulder (Figure 20 7). The RVOT,

458 CHAPTER 20 FIGURE 20 7. Epicardial right ventricular outflow tract view. This view permits visualization of the right ventricular outflow tract (RVOT), pulmonic valve (PV), proximal main pulmonary artery, and aortic valve (AV). Orienting a spectral and color-flow Doppler beam parallel to blood flow permits the evaluation of chamber pressures, and quantification of pulmonic regurgitation or stenosis.this view is also useful for diagnosing a proximal pulmonary embolism or assisting with positioning a pulmonary artery catheter. pulmonic valve (PV), and proximal main pulmonary artery (PA) can be visualized. EPIAORTIC ULTRASOUND IMAGING PLANES The ASESCA recommended comprehensive epiaortic ultrasound examination includes a minimum of five views for the evaluation of the ascending aorta from the sinotubular junction to the origin of the innominate artery, and the aortic arch. 6 The ascending aorta should be assessed in SAX in each of the proximal, mid, and distal segments. A LAX view of the ascending aorta including visualization of the proximal, mid, and distal segments should also be acquired. A LAX epiaortic ultrasound examination of the arch includes visualization of the proximal arch, and ideally all three arch vessel origins. The ASESCA guidelines recommend that the ascending aorta be divided into 12 areas including the anterior, posterior, and left and right lateral walls within the proximal, mid, and distal ascending aorta segments. 6 The proximal ascending aorta is defined as the region from the sinotubular junction to the proximal intersection of the right pulmonary artery (RPA). The mid ascending aorta includes that portion of the aorta that is adjacent to the RPA. The distal ascending aorta extends from the distal intersection of the RPA to the origin of the innominate artery. The diameter of each aortic segment should be measured as the maximum diameter in the SAX orientation, from the near-field inner edge to the far-field inner edge (internal diameter). 6 While epiaortic scanning may be used to evaluate ascending aortic aneurysms and dissection, this technique is most commonly utilized to evaluate the extent of aortic atherosclerotic burden to guide the surgical approach towards cannulation for cardiopulmonary bypass with the intention of avoiding the generation of emboli and excessive aortic trauma. While several grading systems have been recommended, 7-10 a comprehensive epiaortic ultrasonographic examination should include an evaluation of each of the following measurements for each of the three ascending aortic short-axis segments and for the aortic arch: (1) maximal plaque height thickness, (2) location of the maximal plaque within the ascending aorta, and (3) presence of mobile components. Additional measurements indicating the extent of atheroma burden, such as circumferential area of maximal plaque obtained by planimetry, may also be acquired. When plaque area is measured, aortic diameter should also be noted to quantify atheroma burden as a ratio of plaque area to aortic area. 11 Measurements may be repeated as necessary for multiple plaques. Due to the preponderance of data demonstrating an increased risk of adverse neurological outcomes associated with plaques that are greater than 5 mm in thickness, or those that possess a mobile component, 7-10 the presence and location of these plaques should be discussed with the surgeon prior to aortic manipulation.

Page 459 EPICARDIAL ECHOCARDIOGRAPHY AND EPIAORTIC ULTRASONOGRAPHY 459 LAX Examination The LAX orientation is achieved by rotating the probe 90 from the SAX orientation (Figure 20 10). Proximally, the sinus of Valsalva, sinotubular junction, and aortic valve can be visualized. The probe is then advanced distally in a cephalad direction along the aorta, changing the rotation and angulation accordingly to keep the aorta in a longitudinal LAX view (Figure 20 11). Imaging of the ascending aorta should extend towards the aortic arch with visualization of the innominate, left common carotid, and left subclavian artery origins (Figure 20 12). FIGURE 20 8. Short-axis epiaortic ultrasonographic image of the ascending aorta (Asc A). (MPA, main pulmonary artery; LPA, left pulmonary artery; RPA, right pulmonary artery; SVC, superior vena cava.) SAX Examination The ultrasound probe is positioned on the ascending aorta as proximal to the aortic valve as possible, with the orientation marker directed toward the patient s left shoulder to obtain an imaging window that is perpendicular to the LAX of the aorta (Figures 20 8 and 20 9). After identifying the proximal ascending aorta and AV, slowly advancing the probe distally in a cephalad direction along the aorta permits visualization of the mid ascending aorta, and the distal ascending aorta towards the aortic arch at the origin of the innominate artery. Advancing the probe slightly further permits examination of the proximal aortic arch. FIGURE 20 9. Short-axis epiaortic ultrasonographic image of echo-dense atherosclerotic plaque (arrows) in the ascending aorta. (MPA, main pulmonary artery; RPA, right pulmonary artery; SVC, superior vena cava.) EPICARDIAL ECHOCARDIOGRAPHY AND EPIAORTIC ULTRASONOGRAPHY TRAINING GUIDELINES Compared to TEE, epicardial echocardiography and epiaortic ultrasonography are unique in requiring a collaborative effort with the cardiac surgeon to either allow the echocardiographer to guide them in obtaining images, or alternatively permit the echocardiographer to have direct access to the epicardial or epiaortic surface within the operative field. In addition, experience in epicardial echocardiography is considered an important component of advanced, rather than basic, perioperative echocardiographic training. Current guidelines published by the ASE and SCA recommend that epicardial echocardiographic and epiaortic ultrasonographic training should include the study of 25 examinations, of which five are personally directed under the supervision of an advanced echocardiographer, before a trainee should pursue independent interpretation and

460 Page 460 CHAPTER 20 FIGURE 20 10. Long-axis epiaortic ultrasonographic image of the proximal and mid ascending aorta (Asc A). (AV, aortic valve; PA, pulmonary artery.) application of the information to perioperative clinical decision making.5,6 CONCLUSION A comprehensive epicardial echocardiographic and epiaortic ultrasonographic examination can be performed efficiently and safely,12 and may be the most practical intraoperative imaging technique when a TEE probe cannot be inserted or when probe placement is contraindicated. In addition, these techniques may offer better windows for imaging anterior cardiac structures including the aorta, AV, pulmonic valve, and pulmonary arteries, and therefore they may have a favorable influence on perioperative surgical decision making.13-15 Rosenberger et al analyzed the medical records of 6051 consecutive cardiac surgical patients who underwent epiaortic ultrasonography to determine a potential impact on intraoperative surgical decision making.16 The overall impact of epiaortic ultrasonography on surgical decision FIGURE 20 11. Long-axis epiaortic ultrasonographic image of the mid and distal ascending aorta (Asc A), as well as proximal aortic arch (AA). (PA, pulmonary artery; arrow, innominate artery.)

EPICARDIAL ECHOCARDIOGRAPHY AND EPIAORTIC ULTRASONOGRAPHY 461 FIGURE 20 12. Long-axis epiaortic ultrasonographic image of the aortic arch (AA) including the origins of the brachiocephalic (BC) and left common carotid (LC) arteries. making was 4.1%, and included a change in the technique for inducing cardiac arrest during cardiopulmonary bypass in 1.8%, aortic atherectomy or replacement surgery in 0.8%, requirement for off-pump coronary artery bypass grafting in 0.6%, avoidance of aortic crossclamping and use of ventricular fibrillatory arrest in 0.5%, change in arterial cannulation site in 0.2%, or avoidance of aortic cannulation in 0.2%. In addition, the authors noted that the overall stroke rate was lower in patients in whom intraoperative epiaortic ultrasonography was performed, compared with all patients undergoing cardiac surgical procedures. Nonetheless, epicardial and epiaortic imaging do have certain limitations, including a requirement for a sternotomy to permit direct access to the anterior surface of the heart and aorta, the inability to perform continuous monitoring, and the requirement for at least a brief interruption of the surgical procedure. Despite these limitations, a fundamental understanding of the skills required to obtain and interpret epicardial echocardiographic and epiaortic ultrasound images is an advantageous adjunct to intraoperative TEE in performing a comprehensive intraoperative echocardiographic examination. REFERENCES 1. Kallmeyer IJ, Collard CD, Fox JA, Body SC, Shernan SK. The safety of intraoperative transesophageal echocardiography: a case series of 7200 cardiac surgical patients. Anesth Analg. 2001;92(5): 1126-1130. 2. Lennon MJ, Gibbs NM, Weightman WM, Leber J, Ee HC, Yusoff IF. Transesophageal echocardiography-related gastrointestinal complications in cardiac surgical patients. 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