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J Thorac Cardiovasc Surg 2000;120:466-472
© 2000 The American Association for Thoracic Surgery

Surgery for Acquired Cardiovascular Disease

Aortic arch branches are no longer a blind zone for transesophageal echocardiography: A new eye for aortic surgeons

From the First Department of Surgery, Hiroshima University School of Medicine, Hiroshima, Japan.

Address for reprints: Kazumasa Orihashi, MD, First Department of Surgery, Hiroshima University School of Medicine, Kasumi 1-2-3, Minami-ku, Hiroshima, 734-8551 Japan (E-mail: ka-ori{at}mcai.med.hiroshima-u.ac.jp ).

	Abstract

Top Abstract Introduction Patients and methods Results Discussion Conclusion References

 
Objectives: Branch arteries of the aortic arch have been a blind zone for transesophageal echocardiography. Information regarding blood flow, which is important in both planned and emergency operations on the aorta, has therefore been limited. We have established a technique for visualizing these arteries in nearly all cases.
Methods: In 25 consecutive patients requiring either planned or emergency operations on the aorta, the branch arteries were visualized whenever cerebral malperfusion was suspected. Lateral flexion of the probe tip was used when the trachea interfered with visualization of the arteries.
Results: The left subclavian, left and right common carotid, right subclavian, innominate, and left and right vertebral arteries were visualized in 96% (24/25), 92% (23/25), 96% (24/25), 100% (25/25), 84% (21/25), 92% (22/24), and 88% (21/24), respectively. The origin of the innominate artery was visualized in 36% (9/25). In some cases, dissection extended into branch arteries during surgery or during conservative therapy. When the subclavian artery was clamped, retrograde flow was detected in the vertebral artery (steal flow). The cannula for selective cerebral perfusion occasionally was entered into the right common carotid or subclavian artery and obstructed the other branch with a balloon.
Conclusions: The branch arteries of the aortic arch, including the vertebral artery, are no longer a blind zone for transesophageal echocardiography. The information obtained with our new transesophageal echocardiography technique is helpful for diagnosis, monitoring, and decision making during aortic surgery and in critical care medicine. Visualizing these vessels is worth the effort.

	Introduction

Top Abstract Introduction Patients and methods Results Discussion Conclusion References

 
In aortic arch surgery, several monitors are routinely used for detecting cerebral ischemia to prevent neurologic sequelae. They include transcranial Doppler sonography, ^1-3 near-infrared spectroscopy (NIRS), ^1-7 orbital ultrasound, ⁸ electroencephalography, and sensory evoked potentials. ⁷ However, when an ischemic event is detected during cardiopulmonary bypass (CPB) or selective cerebral perfusion (SCP), it is necessary to identify its cause. The possible mechanisms include the following: (1) dissection extending into the branch artery, (2) dissection that has newly developed due to an inserted cannula or to the jet flow during SCP, (3) unbalanced perfusion among 3 arteries when a single pump is used for SCP, (4) kinking of the cannula, (5) occlusion of a branch artery by an inflated balloon, and (6) air embolism. NIRS and orbital ultrasound are limited in that they detect an ischemic event in the carotid artery territory but not one in the basilar artery territory. Transcranial Doppler examination often fails to detect the signal during SCP when the perfusion pressure is low. During deep hypothermia, electroencephalography and sensory evoked potentials become flat and do not reflect cerebral ischemia. On the other hand, the patient with chest trauma or acute aortic dissection is often in too critical condition to be transferred for computed tomography (CT) or angiography even though information on the branch arteries is essential.

These problems would be solved if the arch branch arteries could be visualized at the bedside or in the operating room. The best option is ultrasonography. However, the intraoperative surface echo necessitates a sterile probe and interrupts surgical procedures. In the intensive care unit, visualization of the origin of branch arteries with conventional echocardiography is limited. Although another option is transesophageal echocardiography (TEE), arch vessels have been considered to be a blind zone for TEE.

We have recently established a method of visualizing the branch arteries and vertebral arteries in nearly every case, and we herein discuss the merits and disadvantages of this technique.

	Patients and methods

Top Abstract Introduction Patients and methods Results Discussion Conclusion References

 
We examined 25 consecutive patients who underwent surgery on the thoracic aorta or were referred to the Division of Critical Care Medicine in our institute for emergency TEE. They consisted of 17 men and 8 women whose ages ranged from 24 to 83 years, including 13 patients with aortic aneurysm, 9 patients with aortic dissection, 2 patients with aortitis, and 1 patient with chest trauma. The surgical procedures were as follows: total arch replacement (n = 9), hemiarch replacement (n = 1), aortic root replacement (n = 1), ascending aorta replacement (n = 1), transaortic endovascular stent-grafting (n = 8), descending aorta replacement (n = 2), and ascending aorta bypass to the abdominal aorta and right subclavian artery (n = 1). Aortic dissection was conservatively followed up in 2 patients.

In all patients, TEE was performed with the use of sedation or general anesthesia with respiratory control. In the patients undergoing surgery, regional oxygen saturation in the bilateral frontal lobes was monitored by means of an NIRS system (TOS-96, TOSTEC Co, Ltd, Tokyo, Japan). SCP was established under circulatory arrest at a rectal temperature of 25°C with perfusion cannulas (14F, RC-014-NIB, Research Medical, Inc, Salt Lake City, Utah) inserted from inside the aorta or through a lateral incision of the branch artery. In some cases, the right subclavian artery was cannulated with a thin-walled catheter (8F-14F, SA-08 to SA-14, Kuraray Co, Ltd, Osaka, Japan) or was anastomosed with a vascular prosthesis in a side-to-end fashion. The branch arteries were perfused with a single roller pump through a branched circuit. The flow rate during SCP was basically 200 mL/min per branch and was increased to a total of 1000 mL/min when the perfusion pressure was unusually low or the blood flow was undetectable in the central retinal artery.

A 5-MHz biplane TEE (EUB555, Hitachi Ltd, Tokyo, Japan) was used for visualizing the arch branches in the following manner (Figs 1 and 2). As the probe is withdrawn from the long-axis view of the aortic arch with a slight upward flexion, a short-axis view of the left subclavian artery (on the right) and left common carotid artery (on the left) appears (Fig 1, A ). As the probe is pulled further with the left subclavian artery kept in the view by rotating the probe counterclockwise, the horizontal portion of the left subclavian artery is depicted in its long axis (Fig 1, C ). The left vertebral artery arises around this portion toward the right. At a higher level, the short-axis view of the left vertebral artery is depicted, adjacent to the esophagus and vertebra. In the longitudinal scan, the left subclavian artery is depicted as slightly convex toward the right and gives off the left vertebral artery toward the right (Fig 2, A ).

View larger version (38K): [in this window] [in a new window]   Fig. 1. Schematic illustrations demonstrating scanning planes and corresponding image orientation for visualizing arch branch arteries. The orientation is horizontally flipped from that of a CT scan, as an echographer's view point. The shaded area is the blind zone caused by the trachea. R, Right; L, left; SCA, subclavian artery; CCA, common carotid artery; VA, vertebral artery; IA, innominate artery; IV, innominate vein; T, trachea; V, vertebra; IJV, internal jugular vein; SG, Swan-Ganz thermodilution catheter

View larger version (79K): [in this window] [in a new window]   Fig. 2. TEEs showing arch branches. A, Left subclavian artery (L-SCA) , which gives off left vertebral artery (L-VA) toward the right in the longitudinal scan (L). B, Innominate artery (IA) adjacent to internal jugular vein (IJV) with Swan-Ganz thermodilution catheter (SG) inside in the transverse scan (T). C, Right common carotid artery (R-CCA) and adjacent internal jugular vein (IJV). D, Right subclavian artery (R-SCA), which gives off right vertebral artery (R-VA) toward the left. E, Origin of innominate artery (IA) in longitudinal scan.

View larger version (73K): [in this window] [in a new window]   Fig. 3. Effect of lateral flexion of probe tip in visualizing innominate artery (IA) and left common carotid artery (L-CCA). Although these are in the blind zone, lateral flexion enables them to be visualized from the side of the trachea (T). L-SCA, Left subclavian artery.

The longitudinal scan visualizes the long-axis view of the right common carotid artery. Withdrawing the probe further allows the bifurcation of the right common carotid artery into the internal and external carotid arteries to be visualized. One disadvantage is that the probe may be pulled out of the esophagus, and it may be difficult to reinsert. As the probe is gradually withdrawn from the bifurcation of the right common carotid artery and the right subclavian artery with the latter kept in the view by a clockwise rotation of the probe, the horizontal portion of the right subclavian artery is depicted (Fig 1, F , Fig 2, D ). Contrary to the left side, the right vertebral artery appears on the left close to the vertebra. The longitudinal scan visualizes the right subclavian artery, convex to the right, with the right vertebral artery arising toward the right. The origin of the innominate artery is visualized by advancing the probe with a counterclockwise rotation from the bifurcation level, although the view is often disturbed by the trachea despite lateral flexion of the probe. The origin of the innominate artery can also be visualized in the longitudinal scan of the arch by rotating the probe clockwise from the long-axis view of the origin of the left subclavian artery (Fig 2, E ). Three branch arteries appear in series. When the trachea disturbs visualization, a rightward or leftward flexion of the probe is helpful.

Preoperative diagnosis was reconfirmed with TEE after induction of anesthesia and new extension of dissection was examined. Every branch artery was examined after initiation of CPB and SCP and after the arteries were reconstructed. When unusual data appeared in NIRS and orbital ultrasound, any change in the branch arteries was sought. The patients referred to the Division of Critical Care Medicine of our hospital for trauma or possible circulatory derangement were examined for injury or dissection of the aorta and involvement of branch arteries, presence of cardiac tamponade, pulmonary embolism, or myocardial infarction. The patients with aortic dissection who were conservatively treated were subject to frequent TEE follow-up examinations for new extension of dissection.

	Results

Top Abstract Introduction Patients and methods Results Discussion Conclusion References

 
No complication related to the use of TEE was encountered. The left subclavian, left common carotid, right common carotid, right subclavian, innominate, left vertebral, and right vertebral arteries were visualized in 96% (24/25), 92% (23/25), 96% (24/25), 100% (25/25), 84% (21/25), 92% (22/24), and 88% (21/24), respectively. The origin of the innominate artery was visualized in 36% (9/25).

Patient 1 underwent total arch replacement for arch aneurysm. Good blood flow was detected in the branch arteries before CPB. The right regional oxygen saturation dropped to 55% during SCP (600 mL/min) with the perfusion pressure as low as 20 to 30 mm Hg. TEE revealed that flow through the right common carotid artery was of a to-and-fro pattern. An inadequate perfusion rate was deemed to be responsible. As the SCP flow rate was increased to 800 mL/min, the right common carotid artery flow became antegrade and the regional oxygen saturation improved to 59%.

In patient 3 (stent-grafting), a cannula in the right subclavian artery was visualized during SCP. The blood flow was barely detectable in the right common carotid artery, whereas it was apparent in the right subclavian artery. The regional oxygen saturation dropped to 54%. Regional oxygen saturation and right common carotid artery flow improved when the cannula was pulled and SCP flow rate increased.

In patient 7 (hemiarch replacement for type II dissection), the right radial artery pressure suddenly dropped to nearly zero during CPB. Because tapping of the forearm generated fluctuation of the pressure wave, occlusion between the brachial artery and innominate artery was suggested. Both the cannula tip pressure and the regional oxygen saturation were acceptable. TEE revealed a newly developed dissection at the proximal portion of the innominate artery to the bifurcation, which caused obstruction of the true lumen.

In patient 10, with type I dissection, TEE revealed that the left subclavian artery was perfused from the false lumen and the innominate artery from the true lumen, although dissection was not present in the branch arteries. On the basis of this information, an arterial route was placed on the right subclavian artery.

Patient 11 had had blunt chest trauma. TEE was performed on arrival to rule out an aortic injury because the upper part of the mediastinum was widened on the chest radiograph. An echo-free space was found around the aortic arch and pericardial space. The ascending to descending aorta and 3 branches including their origins proved to be intact. Because clot in the pericardial fluid was present only adjacent to the junction between the superior vena cava and the right atrium and an unusual inward protrusion-like hematoma was found at this area, injury to the cavoatrial junction was deemed to be responsible. The patient was treated conservatively on the basis of these findings. Subsequent CT scanning provided no additional information regarding the cause of mediastinal hemorrhage.

Patient 17, who had an acute cardiac arrest, was referred to our institute for type IIIb dissection with retrograde extension. Because the branch arteries were not involved except at the origin (Fig 4, A ), he was treated conservatively. The next day, TEE revealed an enlarged false lumen and narrowed true lumen although no other sign indicated the need for emergency CT. An emergency operation was done on the basis of the TEE finding. During the operation, a newly developed dissection was found in the right common carotid artery up to bifurcation with the stenosed true lumen (Fig 4, B ).

View larger version (110K): [in this window] [in a new window]   Fig. 4. TEEs showing intraoperative extension of dissection into the right common carotid artery (R-CCA). A, Before operation, dissection is absent. B, During CPB, dissection extended into the right common carotid artery, making a true lumen (TL) compressed by a false lumen (FL). IJV, Internal jugular vein.

View larger version (72K): [in this window] [in a new window]   Fig. 5. TEEs showing converted flow direction in the left vertebral artery (L-VA) after unclamping and reperfusion of the left subclavian artery (L-SCA). Retrograde flow (positive) in the left vertebral artery turned to antegrade (negative) after unclamping.

View larger version (81K): [in this window] [in a new window]   Fig. 6. TEEs showing change of flow pattern in the left subclavian artery (L-SCA) after reconstruction. A, Before operation, dissection is present in the left subclavian artery with an intimal flap inside. B, Blood flow in the left subclavian artery. Flow is detected in both the true lumen (TL) and false lumen (FL). C, After reconstruction, flow is detected only in the true lumen. T, Trachea.

In patient 24, occlusion of the right common carotid artery had been diagnosed preoperatively. The occlusion was reconfirmed with TEE, depicted as an arterial lumen filled with an echogenic mass without a flow signal. When a thermodilution catheter was inserted, the anesthesiologist felt unusual resistance in advancing the guide wire. TEE revealed that the internal jugular vein was also occluded with thrombus. Although the distal portion of the internal jugular vein was patent, the blood flow was of a to-and-fro pattern. The catheter was inserted from the left internal jugular vein.

	Discussion

Top Abstract Introduction Patients and methods Results Discussion Conclusion References

 
The following 3 tips should be mentioned in regard to our method. First, lateral flexion of the probe tip is essential for visualizing the branch arteries when the trachea obstructs the view of the arteries. Second, a transverse scan is used as the first step of visualization because it corresponds well to the CT images and facilitates comprehension of image orientation. Third, the internal jugular vein is helpful for identifying the right common carotid artery. Although several vessels are depicted on the right side (right common carotid artery, right subclavian artery, innominate artery, and internal jugular vein), each vessel is identified by examining continuity of the lumen, merging or branching of vessels, presence of the catheter inside, and direction of blood flow. The images of vessels are clear once they are visualized. The carotid artery can be visualized from the origin and distally up to the bifurcation level, with the probe tip 15 to 20 cm from the incisor, although the probe may be pulled out of the esophagus. The vertebral artery is also visualized from its origin to the above level. The subclavian artery is depicted as far as several centimeters from the origin of the internal thoracic artery. The subclavian artery is suitable for measurement of blood flow because it courses along the ultrasonic beam, while the common carotid artery and vertebral artery course nearly perpendicularly to the scanning plane. The longitudinal scan provides the long-axis view of these arteries and enables Doppler measurements with an angle correction. Thus, the presence, direction, and pattern of blood flow can be assessed. Our method has enabled us to visualize the bilateral common carotid branch arteries and bilateral vertebral arteries in the majority of cases, that is, "bedside 4-vessel study." The arch branches are no longer a blind zone for TEE. The clinical implications of this method are summarized as follows.

The first feature is "diagnosis" in critical care medicine. TEE provides useful information for diagnosing the pathologic conditions and for ruling out several diseases that can be fatal unless diagnosed and treated without delay, including aortic dissection, ruptured aneurysm, pulmonary embolism, cardiac tamponade, and myocardial infarction. TEE examination takes only a few minutes and can be completed while preparing to transfer the patient to the radiology department, or it can be done in patients whose condition is too critical for CT or angiography. In patients with chest trauma, ruling out injury of the aorta or branch arteries allows time for further examination in the intensive care unit or for conservative treatment (patient 11). The diagnostic precision can even be superior to CT in such a case.

The second feature is "intraoperative monitoring." This study has demonstrated that dissection can newly develop or extend during surgery, especially during CPB (patients 7 and 17), that the right common carotid and right subclavian arteries may not be adequately perfused during SCP (patient 3), and that "subclavian steal" occurs during surgery (patient 19). When NIRS or orbital ultrasound indicates cerebral malperfusion, the causative factors related to the branch arteries can be evaluated by TEE (patients 1, 3, and 19). In patient 3, the inflated balloon of the subclavian artery cannula might have occluded the right common carotid artery. Perfusion after surgical reconstruction can be assessed immediately after reperfusion (patient 21). One limitation of this study is that the TEE findings could not be confirmed with other imaging modalities because none is feasible simultaneously in the operating room.

The third feature is "decision making" in both the operating room and intensive care unit. When the subclavian artery is used for an arterial CPB route, dissection in the artery may lead to additional trouble. TEE is helpful in determining which artery to use for the arterial route and in confirming the subsequent adequacy of perfusion (patient 10). Aortic dissection was shown to dynamically change within several days of conservative treatment (patient 17). Because frequent CT examinations in a patient with many infusion lines and a respirator are not practical, TEE can be useful for frequent evaluation of dissection and for avoiding delay in decision making for surgical indications.

This method has several limitations. It is not feasible in awake patients because of discomfort and possible hemodynamic insult. This method also has a learning curve. One needs to comprehend the anatomy of this region and exercise fine manipulation of the probe with both lateral and up-down flexion. However, we have found that a TEE trainee of intermediate level can visualize these vessels after he or she has experienced 10 or 20 cases. Presence of blood flow can be assessed only when the vessel is visualized. On the other hand, absence of flow can be diagnosed only when the lumen is not collapsed and flow is not detected. Although the origin of the innominate artery remains a blind zone in two thirds of patients because it is situated in front of the trachea, the effort to visualize this artery is worthwhile because it can be visualized in one third of cases, and the information is useful when the artery is visualized. However, the risk of injury to the esophagus due to manipulation of the probe is not yet clear, although no such complication occurred in this series. Gentle manipulation is mandatory and further investigation for safety is necessary.

	Conclusion

Top Abstract Introduction Patients and methods Results Discussion Conclusion References

 
The branch arteries of the aortic arch including the vertebral artery are no longer a blind zone for TEE. The information obtained with TEE is helpful for diagnosis, monitoring, and decision making during aortic surgery and in critical care medicine. The effort to visualize these arteries is worthwhile.

	References

Top Abstract Introduction Patients and methods Results Discussion Conclusion References

 

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