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ORIGINAL ARTICLE |
Department of Anesthesia, Far Eastern Memorial Hospital, Taipei, Taiwan
1 Department of Surgery, National Taiwan University Hospital and College of Medicine, Taipei, Taiwan
2 Division of Cardiovascular Surgery, Far Eastern Memorial Hospital, Taipei, Taiwan
3 Department of Anesthesiology, National Taiwan University Hospital and College of Medicine Taipei, Taiwan
Ming-Jiuh Wang, MD, PhD, Tel: +886 2 2356 2010, Fax: +886 2 2321 7522, Email: canon{at}ha.mc.ntu.edu.tw, Department of Anesthesiology, National Taiwan University Hospital and National Taiwan University College of Medicine, 7, Chung Shan South Road, Taipei, Taiwan 100.
ABSTRACT
Aortic dissection is a rare but devastating complication of cardiac operations. The purpose of this investigation was to assess the occurrence of aortic dissection during elective cardiac operations and the usefulness of intraoperative transesophageal echocardiography for the diagnosis and management of this complication. Data of consecutive adult patients undergoing elective cardiac surgery with transesophageal echocardiographic monitoring during an 8-year period were studied retrospectively. Aortic dissection was identified in 7 (0.13%) of 5,247 patients, and diagnosed immediately by transesophageal echocardiography in 5 of them; 2 were diagnosed later by transesophageal echocardiography. All aortic dissections were type A and they occurred after completion of the primary procedure. Two patients treated conservatively died within 5 days. Four of the 5 patients who underwent immediate reoperation survived with serious postoperative complications. Transesophageal echocardiography should be carried out when there is a risk of aortic dissection during cardiac operations, especially in the posterior wall of the ascending aorta, to avoid missing the diagnosis and delaying treatment.
Key Words: Aneurysm • Dissecting • Aorta • Intraoperative Complications • Echocardiography • Transesophageal
INTRODUCTION
Intraoperative aortic dissection is a rare but devastating complication of cardiac operations. The incidence of aortic dissection in cardiac surgical procedures was found to be 0.16% to 0.35% in several retrospective studies, with mortality ranging from 20% to 33%.1–3 In these studies, the diagnosis of aortic dissection was usually based on the finding of a tense circumferential dilatation with bluish discoloration of the ascending aorta. However, some cases were not diagnosed until the manifestation of bleeding or tamponade.1,2 Because these studies were carried out before the routine use of transesophageal echocardiography (TEE), and the dissection was detected mainly by the surgeon, it is not known whether some cases occurred postoperatively or if the diagnosis was delayed due to the lack of TEE.4–8 The purpose of this study was to review our experience in the diagnosis and management of aortic dissection following the routine use of TEE during cardiac operations.
PATIENTS AND METHODS
From August 1997 to July 2005, the surgical records and TEE data of consecutive adult patients undergoing elective cardiac operations in our institution were studied retrospectively. Patients having surgery for aortic dissection or aortic aneurysm and those with aortic dissection caused by femoral cannulation for intraaortic balloon counterpulsation or extracorporeal membrane oxygenation were excluded. Preoperative diagnostic workups including transthoracic echocardiography, cardiac catheterization, and computed tomography were carried out if necessary to confirm the preoperative diagnosis. The study was approved by the institutional review board.
TEE was performed in cardiac surgical patients with a 5-MHz or 6.7-MHz multiplane TEE probe and a CFM 800SV or Vivid 3 or 7 echocardiograph (GE Vingmed, Horten, Norway). The TEE probe was inserted into the esophagus after anesthetic induction and institution of clinical monitoring, unless contraindicated by the existence of esophageal varices or other esophageal disease. TEE was used to confirm the preoperative diagnosis, monitor the status of myocardial contraction and removal of intracardiac air, evaluate the surgical results, and detect any other abnormalities. In addition, the whole length of the thoracic aorta was visualized in mid-esophageal ascending aortic, upper esophageal aortic arch, and descending aortic long- and short-axis views. The images were stored on the hard disk of the echocardiograph. Aortic dissection was defined as the presence of an intima flap in the aorta in at least 2 imaging planes. When aortic dissection was suspected, the surgeon was notified immediately, and the ascending aorta, aortic arch, and descending aorta were evaluated specifically to determine the entry site of the dissection. Management of aortic dissection was at the discretion of the surgeon. The postoperative courses of patients who suffered aortic dissection were analyzed by reviewing their medical records.
RESULTS
During the study period, 5,247 adult patients underwent cardiac surgery, including off-pump coronary artery bypass (OPCAB). Demographic and operative data are listed in Table 1
. TEE was not performed in 25 patients due to difficulty in inserting the probe or the presence of esophageal disease; these patients remained well with no evidence of aortic dissection. Intraoperative aortic dissection was identified in 7 (0.13%) patients whose demographic and operative data are summarized in Table 2. Preoperatively, the ascending aorta was not dilated, and there were no severe atherosclerotic changes. All 7 patients had acute aortic dissection type A (AADA), extending from the ascending to the descending aorta. Intraoperative TEE detected AADA immediately after it occurred in 6 patients; in 5 of them, the lesion was apparent as a tense dilated and bluish ascending aorta within a few minutes of TEE diagnosis. In the other (patient A), the detection of AADA was not confirmed by the surgeon until 30 min after TEE diagnosis. The intimal flap arose in the posterior wall of the ascending aorta and extended anteriorly and up to the aortic arch. One patient (patient D) developed bradycardia with abrupt loss of bilateral femoral artery pulses in the intensive care unit 5 h after aortic valve replacement. Emergency computed tomography revealed AADA with no flow to the left renal and iliac arteries. An immediate reoperation was performed for ascending aortic graft replacement. Careful review of intraoperative TEE images recorded during the primary procedure revealed a small intima flap in the posterior wall of the ascending aorta (Figure 1). All AADA occurred after completion of the primary cardiac procedure: during removal of an aortic cannula in 5 patients, on withdrawing a cardioplegic needle in one, and on release of an aortic partial-occlusion clamp in one (patient F) undergoing OPCAB.
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). In contrast, 4/5 patients who underwent immediate reoperation survived; one (patient B) died due to uncontrollable bleeding after aortic graft replacement. The postoperative courses of the 4 survivors were complicated by sternal wound infection and dehiscence in patient A, acute tubular necrosis, compartment syndrome of the left leg, and paraparesis in patient D, gangrene and amputation of 4 toes of the left foot in patient E, and hoarseness caused by left recurrent laryngeal nerve palsy in patient F. In spite of these complications, they survived with follow-up of 28–68 months. DISCUSSION
Our results reveal that although most aortic dissections were diagnosed by intraoperative TEE immediately after they occurred, a thorough examination of the aorta in standard TEE views, especially of the posterior aortic wall, is necessary to avoid missing a dissection. Before the routine use of TEE in cardiac surgery, recognition of intraoperative aortic dissection required a high index of suspicion, and diagnosis was based on the finding of a tense circumferential dilatation and bluish discoloration of the ascending aorta.1,2 In previous reports, several cases of aortic dissection were not diagnosed until 30 min to 4 h postoperatively, with manifestations of cardiac tamponade, loss of pulse, and massive postoperative bleeding not associated with hypertension.1,2 In this study, surgical inspection did not diagnose AADA immediately after onset in 2 patients. Absence of the typical anterior bluish dilatation of the ascending aorta in patients with posterior aortic wall dissection led to delayed recognition of AADA. Despite one misinterpretation of TEE images, this modality provided an excellent view with high resolution to detect intimal flaps at the posterior wall of the proximal ascending aorta.
TEE has been demonstrated repeatedly to be very useful in the diagnosis of intraoperative aortic dissection.4,5 Several TEE standard views can be used to visualize the proximal ascending aorta, aortic arch, and descending thoracic aorta;9 however, the distal ascending aorta may be inadequately visualized because of the interposed air-filled trachea. In addition to false-negative cases, false-positive diagnosis of aortic dissection might be caused by artifacts involving the ascending aorta. Appelbe and colleagues10 reported that linear artifacts were detected in the ascending aorta in 44% of cases. Color Doppler demonstrates homogeneous color at both sides of the linear echo, indicating the presence of an artifact in the ascending aorta.11
Previous studies demonstrated that the onset of aortic dissection was either shortly after the start of cardio-pulmonary bypass (CPB) or after completion of the primary procedure, with the former resulting from aortic cannulation and the latter from removal of the aortic cannula or cardioplegic needle.1–4 Our experience indicates that decannulation and accompanying aortic manipulation pose a high risk of AADA. The mechanism of aortic dissection after decannulation is most likely related to suture or ligature techniques. During decannulation, ligatures encircling all layers of the aortic wall are crucial. An intimal tear remaining after sealing the adventitia is a potential cause of dissection. Most intimal tears after decannulation occur in the anterior portion of the ascending aorta and can be easily identified by surgeons. In rare circumstances, as found in our study, intimal tears in the posterior portion of the ascending aorta, without a gross aortic anomaly, were difficult to recognized. However, the exact mechanism of posterior aortic wall dissection has not been defined. Cardiovascular anesthesiologists or cardiologists involved in intraoperative TEE should examine every segment of the aorta thoroughly, especially with color-flow Doppler of the posterior wall, to diagnose and enable treatment immediately after the onset of dissection intraoperatively. Based on this experience, we speculate that some aortic dissections diagnosed in the early postoperative period in previous studies might have arisen intraoperatively at the posterior wall, and might possibly have been diagnosed intraoperatively by careful TEE examination.1–3
Aggressive treatment by either graft replacement or direct plication is strongly recommended as soon as possible to eliminate the extremely high risk of rupture of the ascending aorta, even when no active bleeding is present at the onset of aortic dissection. Once dissection is diagnosed, immediate repair of the ascending aorta should be undertaken under hypothermic cardiac arrest after femoral artery cannulation and perfusion has been established. Previous studies have shown that the mortality rate of AADA is 25% to 35% in treated patients and more than 90% if untreated.1,3 Our results confirmed this, and also revealed that the postoperative courses of surviving patients were complicated by serious morbidity and prolonged hospitalization, which may be due to the primary cardiac disease, injury caused by the aortic dissection, and the morbidity associated with additional CPB for reoperation. Another issue that should be addressed is aortic dissection during OPCAB. In our study, one patient who underwent OPCAB and suffered AADA. In this case, a hematoma was found around the proximal anastomosis between a saphenous vein graft and the aorta after release of a partial-occlusion clamp, and dissection of the ascending aorta was diagnosed immediately by TEE. Aortic dissection occurring after removal of a partial-occlusion clamp with or without the use of CPB has been reported previously;2,12 but, to the best of our knowledge, no previous study included patients undergoing OPCAB. Aortic cannulation and partial-occlusion clamps were found to be responsible for over 95% of aortic dissections.2 The much lower incidence of AADA in OPCAB (0.04%) compared to that in operations using CPB and aortic cannulation (0.2%) suggests that aortic cannulation with manipulation of the aorta might be the most important cause of dissection.
We concluded that aortic dissection during cardiac surgery, which occurs mostly in the ascending aorta after the primary procedure, can be diagnosed immediately by TEE, which should be carried out very thoroughly, especially at the posterior wall of the ascending aorta, to avoid missing the diagnosis and thereby delaying treatment.
REFERENCES
Asian Cardiovasc Thorac Ann 2009;
17:408-412
© 2009 by SAGE Publications
DOI: 10.1177/0218492309341784
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