REVIEW ARTICLE
Transesophageal Echocardiographic Imaging of the Branches of the Aorta: A Guide to Obtaining These Images and Their Clinical Utility Pamela Salerno, BBSc, MBBS, FANZCA, Andrew Jackson, MBBS, FANZCA, Martin Shaw, MBBS, FANZCA, Phillip Spratt, MBBS, FRACS, FRCS (Edin), and Paul Jansz, BMed, FRACS, PhD
S
INCE ITS INTRODUCTION INTO widespread clinical use 10 years ago, transesophageal echocardiography (TEE) has played an important role in cardiac surgery. Its function is well established for evaluating structures of the cardiac chambers, valves, and great vessels. More recently, descriptions have appeared in the literature of its use in visualizing the coronary arteries, branches of the aortic arch, and the descending aorta. These vessels are not traditionally imaged during a standard examination as described by the American Society of Echocardiography and the Society of Cardiovascular Anesthesiologists.1 This article provides a summary of the current literature, a practical guide to acquiring the images, and a discussion of the potential clinical applications. This article uses standard nomenclature for probe manipulation as described by Shanewise et al.1 ASCENDING AORTA
Coronary Arteries How To Acquire the Images The left coronary tree. At 0° just above the aortic valve, the left main coronary ostium is seen on the right of the screen at the 2- to 3-o’clock positions (a small degree of anteflexion may sometimes be necessary)2 (Fig 1). Slowly rotate forward to 45° to follow the length of the left main coronary artery until the bifurcation. Once the bifurcation is imaged, the left anterior descending artery (LAD) can be brought into view by retroflexing the probe. This will be seen running downward and to the right of the screen parallel to the interventricular septum3 (Fig 2). Branches originating from the right of the LAD are the diagonal branches, whereas branches originating from the left are the septal perforators.
From St Vincent’s Hospital, Sydney, Australia. Address reprint requests to Pamela Salerno, BBSc, MBBS, FANZCA, Unit 81, 13-15 Potter Street, Waterloo 2017, NSW, Australia. E-mail:
[email protected] Crown Copyright © 2009 Published by Elsevier Inc. All rights reserved. 1053-0770/09/2305-0020$36.00/0 doi:10.1053/j.jvca.2009.05.030 Key words: ttransesophageal echocardiography, visualizing coronary arteries, aortic arch vessels, left internal coronary artery, cardiac surgery, color-flow Doppler, pulse-wave Doppler, anomalous coronary arteries, subclavian artery, posterior intercostal arteries, renal arteries, celiac artery, superior mesenteric artery 694
To visualize the circumflex artery, rotate the beam forward to 45° at the level of the bifurcation. It courses in the left atrioventricular groove, anterior and parallel to the left atrial wall contour3 (Fig 3). By turning the probe to the left, it may be possible to see longer segments and branches of the circumflex artery.2 The first obtuse marginal artery courses to the bottom of the screen, and the left atrial artery courses to the top of the screen. Small alterations in both the ultrasound beam angle and probe position may allow more distal segments of the first obtuse marginal branch to be seen. The distal circumflex artery also can be visualized in the standard midesophageal 2-chamber view as it courses in the left atrioventricular groove. Alternate views of the left coronary tree also can be achieved. From the midesophageal long-axis view, the entire length of the left main coronary artery can be seen at 120° to 160° by turning the probe to the left and using anteflexion.2 The left main coronary artery can be seen originating from the aorta and coursing toward the bottom left of the screen. It also can be seen bifurcating, with the circumflex artery leaving the left main coronary artery and coursing almost horizontally toward the left of the screen and the LAD travelling downward and slightly to the left (Fig 4). The first and second obtuse marginal branches arise from below the circumflex and travel toward the bottom left of the screen. The first and second diagonal branches originate from the left of the LAD, moving toward the bottom left of the screen. The right coronary tree. To assess the right coronary artery (RCA), return to the midesophageal short-axis view of the aortic valve. Withdraw the probe slightly until able to identify the right sinus of Valsalva4 and the right coronary ostia, usually at the 6 to 7 o’clock position. Now rotate forward to between 30° and 65° and apply anteflexion. The RCA can be seen running in the right atrioventricular groove toward the bottom left of the screen2 (Fig 5). Sometimes, a marginal branch can be seen originating from the RCA and running toward the bottom right of the screen. Further forward rotation to produce a long-axis view of the aorta will depict the RCA running vertically from its origin toward the bottom of the screen. Additional lengths of the RCA may be visualized by rotating forward to 110° and 135°. The rates of success in visualizing the coronary arteries using the previously described technique varied among studies (Table 1). It is the authors’ experience that the proximal segments of the main coronary arteries can be visualized in most patients and the images can be obtained typically in 1 to 2 minutes. However,
Journal of Cardiothoracic and Vascular Anesthesia, Vol 23, No 5 (October), 2009: pp 694-701
TEE IMAGING OF THE AORTA
695
Fig 1. The left main coronary artery can be seen originating from the left coronary sinus at the 2- to 3-o’clock positions. Fig 3. The circumflex artery is highlighted. The left main and left anterior descending arteries are not visible.
the more distal segments take considerably longer (5-10 minutes), require more experience, and frequently cannot be imaged. Clinical Utility Assessing the degree of stenosis. The presence of stenosis in the coronary arteries should be assessed with 2-dimensional, color-flow Doppler (CFD) and pulse-wave Doppler (PWD). In 2D, coronary artery stenosis is suggested by an area of localized echo density seen to impinge on the lumen of the vessel.5 To estimate the degree of stenosis, zoom in on the area of interest and freeze the image. Using the calliper, measure both the width of the lumen immediately before the stenosis and compare this with the smallest diameter at the point of stenosis. For ostial lesions, measure the luminal width immediately distal to the narrowing instead. The degree of stenosis is expressed as a percent and is considered hemodynamically significant when greater than or equal to 50%. To define the location of the stenosis, measure its distance from the origin of the coronary ostia for the left main artery and RCA or the distance from the bifurcation in the case of LAD and circumflex artery lesions. When these estimations are complete, apply CFD to the image. Set the Nyquist limit to 50 cm/s when examining the left
Fig 2. The left anterior descending artery (LAD) is highlighted. The left main coronary artery can also be seen. The circumflex artery is not visible.
coronary tree and 20 cm/s for the right coronary tree.6 Normal flow in proximal coronary arteries is laminar and biphasic, with higher velocities in diastole than in systole (Fig 6). Evidence of turbulent flow, depicted by aliasing, is the hallmark of significant upstream stenosis.7 Next, apply PWD to each of the coronary arteries by placing the sample volume in the proximal part of each artery and just distal to any areas of suspected stenosis (from 2-dimensional and CFD). Note that the angle between the ultrasound beam and the vessel is often greater than 20° (Table 2). Normal flow velocities in the coronary arteries are left main coronary artery 36 ⫾ 11 cm/s in systole and 71 ⫾ 19 cm/s in diastole, left anterior descending artery 31 ⫾ 11 cm/s in systole and 67 ⫾ 19 cm/s in diastole, and right main coronary artery 25 ⫾ 8 cm/s in systole and 39 ⫾ 12 cm/s in diastole.6 These normal values, however, have not been validated for the anesthetized patient. The maximal-to-prestenotic velocity ratio for each lesion may also be calculated. A ratio greater than or equal to 2 is suggestive of significant stenosis.
Fig 4. The left main (LM), left main bifurcation, left anterior descending artery (LAD), and circumflex artery (Cx) can be seen. Some other structures are labelled to aid orientation of this nonstandard view: LA, left atrium; Ao, aorta; RVOT, right ventricular outflow tract.
696
SALERNO ET AL
Fig 6. Pulse-wave Doppler image of a normal circumflex artery. In this case, blood flow is clearly diastolic-dominant.
Fig 5. The right coronary artery is highlighted. The extended segment seen in this patient is not routinely visible.
Identification of stenoses also may be accomplished using a modified continuity equation7: stenosis (%) ⫽ 100 ⫻ (1 ⫺ prestenotic VTId) ⁄ (stenotic VTId) where VTId is the diastolic velocity integral. Vrublevsky et al7 found that the success of the continuity equation for identification of stenosis was 88% for the left main coronary, 96% for the left anterior descending (100% for occlusions), 95% for the left circumflex (100% for occlusions), and 83% of right coronary artery (84% for occlusions) (Table 3). The authors also found that the degree of stenosis calculated using the continuity equation correlated well with those concluded by angiography. The correlation
Table 1. Success Rates (%) for the Visualization of Coronary Arteries
Left main Origin Proximal course Entire length LAD Origin Proximal Mid Distal Diagonals D1 D2 Circumflex Proximal Mid Distal Obtuse marginals OM1 OM2 Right coronary artery Origin Proximal Mid Distal
Kasprzak4
Vreblevsky7
Samdarshi5
Tardif 2
99.5
100
93
100 100 100
96.7
96 77
93
69 31 16 25 16
98.6
77
93
80 51 20 18 11
65
72
49
84 16 11
coefficients were 0.82 for the left main, 0.84 for the left anterior descending, 0.85 for the circumflex, and 0.84 for the right coronary artery. In addition, the authors determined a simplified method for diagnosing hemodynamically significant (⬎50%) stenoses. They noted that peak diastolic velocity increases as the degree of stenosis increases. They determined the following values that correlated with stenosis of ⬎50%: left main ⬎1.4 m/s, left anterior descending ⬎0.9 m/s, and circumflex ⬎1.1 m/s. Values for the right coronary artery could not be determined. Coronary angiography will remain the gold standard for diagnosing coronary artery stenosis, but TEE can be useful in cases in which angiography has not been performed. One reported case described a severe left main stenosis diagnosed by TEE (later confirmed by angiography) during an open abdominal aortic aneurysm repair.6 A second case described another severe left main stenosis diagnosed by TEE (also later confirmed by angiography) before a double-valve replacement in a younger patient.8 Anomalous coronary arteries. Transesophageal echocardiographic imaging of the coronary arteries may be useful in delineating the origin, proximal course, and flow characteristics in anomalous coronary arteries.9 Congenital abnormalities of the coronary tree are identified in approximately 1% of patients undergoing coronary angiography.3 Because angiography does not always allow precise delineation of the course of anomalous coronary vessels or define their anatomic relationship with the aorta and pulmonary trunk, TEE may not only provide complementary information to the coronary angiogram, but it also may become an investigative tool in its own right. TEE can accurately identify 3 clinically significant patterns of anomalous coronary arteries.9 First, the passage of a coronary artery between the aorta and the pulmonary artery (the
Table 2. Success Rates (%) of Reported Studies of Performing Pulse-Wave Doppler Analysis of the Coronary Arteries
Left main LAD Circumflex RCA
Kasprzak4
Vreblevsky7
Tardif2
88 85 58 65
97 96 69 48
82 77 53 58
TEE IMAGING OF THE AORTA
697
Table 3. Sensitivity and Specificity of TEE in the Diagnosis of Significant Coronary Artery Stenosis Vreblevsky7
Sensitivity Left main LAD Circumflex RCA Specificity Left main LAD Circumflex RCA
Samdarshi5 Overall
If Visualized (colour flow)
Overall
Tardif2 2D
PWD
Overall
If Visualized (2D)
80% 32 50 *
88 97 95 83
96 79 75 100
96 48 67 37
92 64 75 43
92 48 67 37
100 80 89 82
97 92 92 *
98 67 92 97
99 99 100 100
99 99 100 100
100 86 84 81
100 84 83 75
100 100 100 100
*Could not be calculated because of the prevalence of occlusion.
so-called intermediate course) may be seen. Second, an acute angle of takeoff from the aorta may be seen. Third, it may identify the origin of the coronary artery from the pulmonary artery. These patterns are associated with acute myocardial infarction and sudden death. An interesting finding with PWD in patients with intermediate course and acute angle of takeoff was that blood flow was systolic-dominant.9 This suggests impaired diastolic flow may be the mechanism by which these anomalies give rise to symptoms. A previous case showed the utility of TEE in this area. Intraoperative TEE in a 64-year-old woman scheduled for aortic valve replacement found an anomalous left main with intermediate course (not diagnosed on preoperative angiography).10 As a result of this finding, she also underwent grafting of the LIMA to LAD and made an uneventful recovery.
Select a depth of 6 cm then obtain the standard long-axis view of the aortic arch at 0°. Slowly withdraw the probe until
the arch vessels begin to appear in the short axis. Anteflexion is often needed to obtain a clear view. Delineation of the vessels is greatly aided by using CFD (the authors routinely use CFD over the entire field with a Nyquist limit of 20 cm/s). The left subclavian artery appears on the right of the screen, the left common carotid artery in the center, and the innominate artery on the left (Fig 7). Occasionally, flexing to the left improves imaging of the arch vessels. Next, turn the probe to the left to center the image on the left subclavian artery. Keeping the depth at 6 cm and the CFD on, withdraw the probe until the vessel appears in the long axis (it will be slightly convex to the right of the screen). Anteflexion often aids imaging of the vessel and its branches. The left vertebral artery is the first branch. It arises from the vessel on the right, upper part of the screen. In some patients, the costocervical and thyrocervical trunks also can be imaged arising from the left subclavian artery and running to the right of the screen. The left internal mammary artery (LIMA) is the only vessel that arises from the left subclavian artery to the left of the screen. Imaging of the LIMA is detailed separately later because of its clinical significance. The left common carotid artery and left internal jugular vein can be imaged in the short-axis view by withdrawing the probe and
Fig 7. The aortic arch vessels are highlighted (LCCA, left common carotid artery; LSCA, left subclavian artery). Note that the origin of the innominate artery as seen here is not routinely visible, and the innominate vein is unusually prominent.
Fig 8. The bifurcation of the common carotid artery (CCA) can be seen (ECA, external carotid artery; ICA, internal carotid artery; IJV, internal jugular vein). (Color version of figure is available online.)
AORTIC ARCH
Arch Vessels How To Acquire the Images
698
turning it to keep the vessels in the center of the screen. With the probe at the level of the left common carotid artery bifurcation, a long-axis view can be obtained by rotating forward to 90° (Fig 8). From the long-axis view, PWD measurements can be made in the left common carotid artery, left external carotid artery, and left internal carotid artery. The left internal carotid artery can be distinguished from the left external carotid artery by its lowresistance flow pattern and its location on the screen furthest from the probe. It is important to note that the probe will be above the level of the upper esophageal sphincter when imaging the carotid bifurcation, and the safety of this maneuver has not been formally established. To visualize the right-sided vessels, return to the long-axis view of the left subclavian artery. Then, turn the probe to the right until the right-sided images begin to appear. This takes some practice because all landmarks are initially lost when the trachea is interposed between the probe and the vessels. Anteflexion and right flexion improve the image in some patients. Between the vertebra on the left of the screen and the trachea on the right, the right common carotid artery, right subclavian artery, and the internal jugular vein appear in sequence. Follow the right common carotid artery cephalad to its bifurcation into the right internal and external carotid arteries by withdrawing the probe.11 The right subclavian artery and its branches can be imaged and appear as a mirror image of the left subclavian artery described earlier. Flow characteristics of the aortic arch vessels also can be obtained. Blood flow in the subclavian arteries has a highresistance pattern with systolic antegrade flow, short early diastolic reversal, and no antegrade diastolic flow.12 Conversely, the carotid and vertebral arteries have a low-resistance pattern with antegrade flow in systole and diastole.12,13 Success rates for imaging of aortic arch branches are scarcely quoted in the literature. Earlier studies quote rates of about 70% for the left subclavian artery, left common carotid artery, and left vertebral artery.12,13 A later study indicated greater success, with rates of greater than 90% for the left and right subclavian arteries, right and left common carotid, and left vertebral artery.11
Fig 9. The left internal mammary artery (LIMA) and the left subclavian artery (LSCA) are highlighted. Note that the LIMA is the only branch of the LSCA that courses to the left of the screen.
SALERNO ET AL
Fig 10. Pulse-wave Doppler image of the left internal mammary artery (LIMA) pregrafting to the left anterior descending artery. In this case, the LIMA shows a high-resistance flow pattern with almost entirely systolic flow.
The authors conducted a prospective audit of the ability to image branches of the aortic arch in 50 consecutive cardiac surgical patients undergoing LIMA-to-LAD grafting. The authors found the following success rates: left subclavian artery, 100%; left vertebral artery, 100%; LIMA post-grafting to LAD, 90%; left common carotid artery, 98%; innominate artery origin, 26%; innominate artery bifurcation, 68%; right subclavian artery, 62%; and right common carotid artery, 70%. Left Internal Mammary Artery How To Acquire the Images To image the LIMA, start from the long-axis view of the left subclavian artery as described above. Keep the depth at 6 cm and rotation at 0°, and use CFD over the entire screen with a Nyquist limit of 20 cm/s. As noted earlier, the LIMA is the only vessel that arises from the left subclavian artery to the left of
Fig 11. Pulse-wave Doppler image of the left internal mammary artery (LIMA) after grafting to the left anterior descending artery (LAD). In a normal LIMA-LAD graft as shown here, the blood flow pattern is analogous to a coronary artery (ie, diastolic-dominant).
TEE IMAGING OF THE AORTA
the screen (Fig 9). This is an important clinical point and greatly aids identification of the vessel. The LIMA appears in the long axis, coursing to the left of the screen toward the left subclavian vein (it then passes inferior to the vein). Slight anteflexion is often useful in imaging the LIMA. To measure blood flow velocity, place the sample volume in the artery, at least a few millimeters distal to the origin to avoid collecting the signal from the left subclavian artery. Normally, the LIMA shows a high-resistance flow pattern with almost entirely systolic flow (Fig 10). When the LIMA is used as a conduit and grafted to the left anterior descending coronary artery, the flow characteristics change. Blood flow in the LIMA becomes diastolic-dominant (Fig 11). The authors have found that there is a steep learning curve when imaging the LIMA, but with practice a high success rate can be achieved. Successful imaging of the LIMA was achieved in 90% of patients studied by Orihashi et al.14 This success rate was the same as that found by the authors in their audit described earlier.
699
posterior intercostal artery. When identified, rotate forward to 90° so that the artery can be visualized in both the short- and long-axis view.16 Continue withdrawing the probe slowly. The posterior intercostal arteries will appear in sequence. Identify both the right and left intercostal artery at each level. In the longitudinal view, it is possible to image 2 to 3 posterior intercostal arteries simultaneously. Use PWD to characterize flow. There will be a high-resistance flow pattern with prominent and sharp antegrade systolic flow and little or no flow in diastole. Doppler interrogation will assist in distinguishing the posterior intercostal arteries from other branches of the abdominal and thoracic aorta. The celiac, superior mesenteric, renal, and bronchial arteries all show low-resistance flow patterns.16 Clinical Utility Currently, there are no known clinical applications for imaging of the posterior intercostal arteries. ABDOMINAL AORTA
Clinical Utility Transesophageal echocardiographic assessment of the aortic arch and its branches has numerous clinical applications. First, it can be used to diagnose dissection and malperfusion of arch vessels before or after cardiopulmonary bypass. It also can confirm cannula position and assess flow. During surgery involving the aortic arch, TEE can confirm flow in the carotid arteries.11 TEE also can be used to assess perfusion after surgical reconstruction of the aortic arch. Second, TEE can diagnose LSCA stenosis as described in a previous case report.15 LSCA stenosis can lead to recurrent angina after in situ LIMA-to-LAD grafting because of retrograde blood flow from the LIMA into the LSCA. LSCA stenosis is present in around 1% of patients undergoing ultrasound examination.15 In the presence of significant LSCA stenosis (or occluded LSCA), the LIMA can be used as a free graft. Finally, TEE can be used to assess the flow pattern in the LIMA after grafting to the LAD. The flow pattern should become that of a coronary artery (Fig 6) (ie, diastolic-dominant). Diastolic-dominant flow is defined as a ratio of diastolic velocity time integral-to-systolic velocity time integral of greater than 1.14 This ratio has been shown to be highly sensitive and specific for adequate graft perfusion.13 Systolic dominant flow or equivalent systolic-to-diastolic flow may be indicative of graft stenosis or occlusion.
Renal Arteries To visualize the renal arteries, start with a standard transgastric short-axis view of the left ventricle. Next, return the probe to the neutral position and turn it 180° to the right so that it faces posteriorly. A kidney should be seen at the bottom left of the screen (Fig 12). If not, advance the probe a further 5 to 10 cm and turn the probe to the right. The right and left kidney should be easily distinguishable by their anatomic relationship to the liver on the right and the spleen on the left.17 Add CFD to confirm blood flow and then align the PWD sampling beam to characterize the flow. Renal blood flow has a low-resistance pattern with prominent antegrade flow in both systole and diastole.16 The Celiac and Superior Mesenteric Arteries To visualize the celiac artery, begin with a short-axis view of the abdominal aorta. Advance the probe slowly. The celiac artery will appear in the 1 o’clock position, arising
DESCENDING THORACIC AORTA
Posterior Intercostal Arteries How To Acquire the Images Advance the probe into the stomach, and turn the probe until the aorta is seen in short axis. Note that the abdominal aorta can be differentiated from the descending thoracic aorta by an increase in distance between the probe and the aorta once the probe passes below the diaphragm and into the stomach. Place CFD on the screen, and start withdrawing the probe slowly. The first branch arising from the aorta should be the last
Fig 12. The renal artery is highlighted. The renal medulla and cortex also are shown. (Color version of figure is available online.)
700
SALERNO ET AL
Fig 13. The abdominal aorta and celiac artery are highlighted. The celiac artery courses away from the aorta and has an early branch visible. (Color version of figure is available online.)
from the aorta (Fig 13). The celiac artery should be seen dividing into branches almost immediately and moving away from the aorta.18 PWD interrogation will show a low-resistance flow pattern with prominent antegrade flow in both systole and diastole.16 The superior mesenteric artery should be sought after visualization of the celiac artery. Advance the probe slowly from the level of the celiac artery. The superior mesenteric artery should appear at the 3 o’clock position. It is distinguishable from the celiac by the fact that it remains adjacent to the aorta in its course rather than moving away from it.18 Blood flow in the superior mesenteric artery also shows a low-resistance pattern.16 Alternate views of the celiac and superior mesenteric arteries can be obtained by rotating forward to 90°. Clinical Utility Garwood et al17 found that it was possible to detect changes in renal blood flow patterns during coronary artery bypass graft surgery. PWD recordings were made of the renal arteries and then repeated after the initiation of a dopamine infusion. Pulsatility and resistive indices were calculated. Reductions in
these indices were indicative of a reduction in renal vascular resistance. Garwood et al suggested that renal artery imaging may be useful for measuring renal blood flow in the perioperative period. Intraoperative detection of atherosclerotic embolization to the renal artery already has been described.18 Renal dysfunction is a common problem in the population presenting for cardiac surgery and brings with it significant morbidity and mortality. Further research may find an increasing role for TEE as an intraoperative monitor of renal blood flow. TEE can be used to assess dissection and atheroma in the celiac and superior mesenteric arteries and to assess blood flow before and after surgery of these arteries.18 TEE can also be used to diagnose mesenteric ischemia. Fiore et al19 used TEE intraoperatively to measure blood flow in the superior mesenteric artery of 19 patients undergoing off-pump coronary artery bypass graft surgery, showing that the measurement of blood flow distribution to splanchnic viscera was feasible and noting reduced flow during cardiac displacement. Similarly, Orihashi et al20 in a small study of patients with acute aortic dissection found imaging of the superior mesenteric and celiac arties to be almost 100% successful and the information gained to be 100% sensitive and specific in diagnosing clinically apparent intestinal ischemia.
CONCLUSION
TEE is a minimally invasive and reliable diagnostic tool, providing anatomic and functional information of the heart and great vessels. The scope of this imaging technique has slowly broadened to include the branches of the aorta. Proximal segments of the coronary arteries can be visualized quite consistently. The extent of dissection in the aorta and its branches can be assessed accurately. The blood flow pattern in the LIMA after grafting to the LAD can be characterized. With increasing experience among users and improving quality of TEE probes, evaluation of the aortic branches may become a more routine component of the standard TEE examination.
REFERENCES 1. Shanewise JS, Cheung AT, Aronson S, et al: ASE/SCA guidelines for performing a comprehensive intraoperative multiplane transesophageal echocardiography examination: Recommendations of the American Society of Echocardiography Council for Intraoperative Echocardiography and the Society of Cardiovascular Anesthesiologists Task Force for Certification in Perioperative Transesophageal Echocardiography. J Am Soc Echocardiogr 12:884-900, 1999 2. Tardif JC, Vannan MA, Taylor K, et al: Delineation of extended lengths of coronary arteries by multiplane transesophageal echocardiography. J Am Coll Cardiol 24:909-919, 1994 3. Kasprzak JD, Kratochwil D, Peruga JZ, et al: Coronary anomalies diagnosed with transesophageal echocardiography: Complementary clinical value in adults. Int J Cardiac Imaging 14:89-95, 1998 4. Kasprzak JD, Drozdz J, Peruga JZ, et al: Definition of flow parameters in proximal nonstenotic coronary arteries using transesophageal Doppler echocardiography. Echocardiography 17:141150, 2000
5. Samdarshi TE, Nanda NC, Gatewood RP, et al: Usefulness and limitations of transesophageal echocardiography in the assessment of proximal coronary artery stenosis. J Am Coll Cardiol 19:572-580, 1992 6. Theunissen T, Coddens J, Foubert L, et al: Intraoperative severity assessment of coronary artery stenosis in patients at risk: the role of transesophageal echocardiography. Anesth Analg 102: 366-368, 2006 7. Vrublevsky AV, Boshchenko AA, Karpov RS: Diagnostics of main coronary artery stenoses and occlusions: Multiplane transesophageal Doppler echocardiographic assessment. Eur J Echocardiography 2:170-177, 2001 8. Firstenberg MS, Greenberg NL, Lin SS, et al: Transesophageal echocardiography assessment of severe ostial left main coronary stenosis. J Am Soc Echocardiogr 13:696-698, 2000 9. Dawn B, Talley JD, Prince CR, et al: Two-dimensional and Doppler transesophageal echocardiographic delineation and flow characterization of anomalous coronary arteries in adults. J Am Soc Echocardiogr 16:1274-1286, 2003
TEE IMAGING OF THE AORTA
10. Tolley PM, Bolsin SN: Diagnostic dilemmas in intraoperative echocardiography. J Cardiothorac Vasc Anaesth 15:793-794, 2001 11. Orihashi K, Matsuura Y, Sueda T, et al: Aortic arch branches are no longer a blind zone for transesophageal echocardiography: A new eye for aortic surgeons. J Thorac Cardiovasc Surg 120:466-472, 2000 12. Katz ES, Konecky N, Tunick PA, et al: Visualization and identification of left common carotid and left subclavian arteries: A transesophageal echocardiographic approach J Am Soc Echocardiogr 9:58-61, 1996 13. Nanda NC, Thakur AC, Thakur D, et al: Transesophageal echocardiographic examination of left subclavian artery branches. Echocardiography 16:271-77, 1999 14. Orihashi K, Sueda T, Okada K, et al: Left internal thoracic artery graft assessed by means of intraoperative transesophageal echochardiography. Ann Thorac Surg 79:580-584, 2005
701
15. Mukhtar OM, Miller AP, Nanda N, et al: Transesophageal echocardiographic identification of left subclavian artery stenosis with steal phenomenon. Echocardiography 17:197-200, 2000 16. Ravi BS, Nanda NC, Htay T, et al: Transesophageal echocardiographic identification of normal and stenosed posterior intercostal arteries. Echocardiography 20:609-615, 2003 17. Garwood S, Davis E, Harris SN: Intraoperative transesophageal ultrasonography can measure renal blood flow. J Cardiothorac Vasc Anaesth 15:65-71, 2001 18. Orihashi K, Matsuura Y, Sueda T, et al: Abdominal aorta and visceral arteries visualized with transesophageal echocardiography during operations on the aorta. J Thorac Cardiovasc Surg 115:945-947, 1998 19. Fiore G, Brienza N, Cicala P, et al: Superior mesenteric artery blood flow modifications during off-pump coronary surgery. Ann Thorac Surg 82:62-68, 2006 20. Orihashi K, Sueda T, Okada K, et al: Perioperative diagnosis of mesenteric ischemia in acute aortic dissection by tranesophageal echocardiography. Eur J Cardiothorac Surg 28:871-876, 2005
