Ann Thorac Surg 2005;80:316-318
© 2005 The Society of Thoracic Surgeons
Case report
Aortic Dissection With Potential Origin From a Mechanical Bypass Anastomosis
Martin Zinkernagel, MD,
Markus J. Wilhelm, MD,
Reza Tavakoli, MD,
Marko I. Turina, MD,
Michele Genoni, MD*
Department of Cardiovascular Surgery, City Hospital Triemli, Zurich, Switzerland
Accepted for publication December 10, 2003.
* Address reprint requests to Dr Genoni, Department of Cardiovascular Surgery, City Hospital Triemli, Birmensdorfer Str 497, 8063 Zurich, Switzerland (Email: michele.genoni{at}triemli.stzh.ch).
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Abstract
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Ascending aortic dissection is a known complication of cardiac surgery. Off-pump coronary artery bypass surgery seems to be associated with a higher risk for this event as compared with on-pump bypass surgery. This increased risk may result from aortic side-clamping under pulsatile flow as opposed to continuous flow in conventional bypass surgery. Mechanical devices allowing performance of proximal bypass anastomoses without aortic side-clamping are supposed to reduce the risk for aortic dissection. We report a case in which ascending aortic dissection occurred 8 days after off-pump bypass surgery, most likely arising from a mechanically performed proximal bypass anastomosis.
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Introduction
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Aortic dissection is a rare complication of cardiac operations and is associated with a high mortality rate [1]. It has been reported at an incidence of as high as 0.16% and may occur at any time after cardiac surgery, ranging from an immediate intraoperative manifestation to years postoperatively [1–3]. Various risk factors including hypertension, age, inherited connective tissue disorders, aortic arteriosclerosis, and thin or dilated aortic walls have been identified [4, 5]. Predisposing locations for the origin of aortic dissections after cardiac surgery are the areas of surgical maneuvers such as cannulation, cross-clamping, and side-clamping of the ascending aorta and the site of the proximal anastomosis [1, 6]. We report the case of a 65-year-old woman in whom acute ascending aortic dissection developed 8 days after off-pump coronary artery bypass graft surgery (OPCAB). The dissection had immediate contact to the proximal bypass anastomosis, which was performed without aortic side-clamping using the Symmetry Bypass System Aortic Connector (St. Jude Medical, St. Paul, MN).
A 65-year-old woman with unstable angina was referred to our center for coronary angiography. The patient’s vascular risk factors included nicotin abuse and hypertension. Cardiac catheterization revealed three-vessel disease with complete occlusion of the right coronary artery and left anterior descending artery, 95% stenosis of the diagonal branch, and 95% stenosis of the circumflex artery. The left ventricular angiography showed a reduced left ventricular function with an ejection fraction of 35%. Complete off-pump coronary revascularization was performed. The left saphenous vein was harvested endoscopically, and both internal mammary arteries were prepared. As the left mammary artery did not have sufficient flow despite local treatment with vasodilators, it could not be used. The right internal mammary artery was grafted to the posterolateral branch of the circumflex artery (intraoperative flow 26.6 mL/min). One vein graft was anastomosed sequentially to the left anterior descending artery and a diagonal branch (intraoperative flow 29 mL/min). A second venous bypass was grafted to the posterior descending artery (intraoperative flow 23 mL/min). Both vein grafts were implanted into the ascending aorta using the Symmetry Bypass System Aortic Connector before the distal anastomoses were performed.
The intraoperative and postoperative course was uneventful. Transesophageal echocardiography at the end of the operation revealed a slightly improved left ventricular function as compared with preoperatively; the ascending aorta was normal with a diameter of 3.9 cm. On the first postoperative day, the patient was transferred from the intensive care unit to the regular ward. Eight days postoperatively, the patient was discharged to a rehabilitation center. Examinations before discharge, including chest roentgenogram, were normal, blood pressure was 120/80 mm Hg with nifedipine 30 mg daily, captopril 6.25 mg twice daily, and sotalol 40 mg twice daily.
The initial physical examination on admission at the rehabilitation clinic revealed no abnormalities, including a normal blood pressure. On the evening of the same day, the patient was found unconscious with nonreacting pupils and loss of the left femoral pulse. Transthoracic echocardiography showed a widening of the ascending aorta and aortic insufficiency. The patient was transferred to a local hospital for computed tomography of the chest, which demonstrated ascending aortic dissection with immediate involvement of one of the proximal anastomoses (Fig 1). The dissection extended into the left carotid artery, compromising cerebral perfusion severely. Owing to these findings and the correlating clinical symptoms, it was decided not to attempt surgical repair. One day later, the patient died from her cerebral injury. An autopsy could not be obtained.
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Fig 1. Aortic dissection with immediate involvement of the proximal vein graft anastomosis (computed tomography scan on postoperative day 8).
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Comment
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During on-pump coronary artery bypass graft surgery (CABG), the aortic side-clamping for performing proximal anastomoses creates a potential site for the development of ascending aortic dissection. It may result from intimal injury due to direct laceration, torsion, or mechanical compression. There might be a higher risk for this complication in OPCAB as compared with CABG. In a recent study, acute ascending aortic dissection was found to have an incidence of 0.04% after CABG using cardiopulmonary bypass, and a significantly higher frequency of 0.97% after OPCAB [7]. That might be, at least in part, due to the fact that in OPCAB, aortic side-clamping for performing the proximal anastomoses is done under normal blood pressure and pulsatile conditions. In contrast, in CABG the proximal anastomoses are performed during extracorporeal circulation, which provides continous flow and a blood pressure that is lower than normal. Thus, in OPCAB the risk for the development of intimal tears may be increased. As a consequence, various strategies are recommended to minimize the risk for aortic wall injury after side-clamping, such as decreasing the systolic arterial pressure below 100 mm Hg at the time of positioning and removal of the side-clamp, avoiding torsion of the side-clamp, and performing the proximal anastomoses during one single side-clamping period.
Furthermore, to avoid this potential complication, efforts have been made to develop mechanical devices that allow performing the proximal anastomoses without aortic side-clamping. For this purpose, the Symmetry Bypass System Aortic Connector was introduced into the clinical arena and has been shown to markedly minimize aortic manipulation during performance of the proximal bypass anastomoses and to reduce the incidence of embolic events from the ascending aorta [8]. However, nothing has been known so far about the potential risk for dissection of the ascending aorta after the use of a mechanical device for proximal anastomoses. The case reported here suggests that a mechanically performed proximal anastomosis can be the origin of dissection of the ascending aorta. One potential reason could be incompletely extracted aortotomy cores. Thus, it might be important to control the core plug in the aortic cutter before deployment of the device to ensure that no intimal flaps are created. Despite this potential complication, the application of such devices may reduce the overall incidence of complications resulting from manipulation of the ascending aorta.
The present case underlines the need for long-term follow-up of patients in whom mechanical devices for proximal anastomoses were used, to check for the potential development of late aortic dissection; and it emphasizes the importance of identifying predisposing factors that might help select appropriate patients for the application of such devices.
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References
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- Boruchow IB, Iyengar R, Jude JR. Injury to asdending aorta by partial-occlusion clamp during aorta-coronary bypass J Thorac Cardiovasc Surg 1977;73:303-305.[Abstract]
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- Eckstein FS, Bonilla LF, Englberger L, et al. The St Jude Medical symmetry aortic connector system for proximal vein graft anastomoses in coronary artery bypass grafting J Thorac Cardiovasc Surg 2002;123:777-782.[Abstract/Free Full Text]
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Abstract
Introduction
