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Ann Thorac Surg 2002;74:S1821-S1824
© 2002 The Society of Thoracic Surgeons
a Department of Cardio-Thoracic Surgery, Nagoya University Graduate School of Medicine Nagoya, Japan
b Department of Radiology, Aichi Medical University, Nagoya, Japan
* Address reprint requests to Dr Usui, Department of Cardio-thoracic Surgery, Nagoya University Graduate School of Medicine, 65 Tsurumai, Showa-ku, Nagoya, 466-8550, Japan
e-mail: ausui{at}med.nagoya-u.ac.jp
Presented at the Aortic Surgery Symposium VIII, May 2–3, 2002, New York, NY.
Abstract
BACKGROUND: Endovascular stent grafting through a median sternotomy for a distal arch aneurysm (the frozen elephant trunk procedure) is an alternative to synthetic graft replacement. But spinal cord dysfunction can easily occur as a complication after surgery. Although its cause is uncertain, some attempts at prevention have been instituted. We address the mechanism of spinal cord dysfunction and evaluate the efficacy of our preventive measures.
METHODS: There were 22 men and 2 women with an average age of 71 (59 to 83) years. There were 22 true aneurysms (13 fusiform, nine saccular), one chronic dissection, and one penetrating aortic ulcer. The following strategies for prevention of spinal cord dysfunction were utilized: low flow perfusion through both axillary arteries (n = 10); pigtail catheter guidance (n = 19); use of a shorter graft with anchoring sutures (n = 12); flooding of the operative field with carbon dioxide (n = 7); aortic unclamping (n = 7), and use of ultra-thin woven Dacron grafts (n = 15).
RESULTS: There was no operative mortality, but cerebrospinal dysfunction complicated four cases (17%): one paraplegia, one stroke along the basilar artery, and two cases of temporary spinal cord dysfunction (paresthesia of the right leg and urinary disturbance). Cerebrospinal dysfunction tended to occur in fusiform aneurysms (31%, p = 0.044). Except when low flow antegrade perfusion through both the axillary arteries was utilized, which resulted in no cases of paraplegia or paraparesis (p = 0.064), the methods used for prevention of cerebrospinal dysfunction appeared to have little efficacy.
CONCLUSIONS: Cerebrospinal dysfunction is a serious complication of the frozen elephant trunk procedure. Its cause has not been clarified, but it tends to occur in fusiform-type aneurysms. Antegrade perfusion through both axillary arteries while the aorta is open may be helpful in its prevention.
Endovascular covered stent grafting (EVG) through a median sternotomy has previously been described by Kato and colleagues [1] and some modifications have been reported [2, 3]. This technique (the frozen elephant trunk procedure) is just like a standard elephant trunk procedure except that it uses a metal stent. This procedure reduces operative risk, but a relatively high incidence of spinal cord dysfunction has been reported. Although its exact cause has not been clarified, the importance of its prevention is generally accepted.
We have utilized the frozen elephant trunk technique since 1997, and several measures aimed at spinal cord protection have been introduced. Pigtail catheter guidance for smooth insertion of the EVG has been utilized since 1998. A shorter EVG with anchoring sutures has been used since 1999. Brain protection has been changed from retrograde cerebral perfusion (RCP) to antegrade perfusion through both axillary arteries since 2000. Flooding of the operative field with carbon dioxide has been used to avoid air embolization in some cases. The techniques outlined have been used with the hypothesis that spinal cord dysfunction may be caused by embolization to the vertebral circulation of air or debris. In this study, we present our experience of spinal cord dysfunction as a warning message and evaluate the clinical efficacy of our preventive methods to address the possible mechanism of spinal cord dysfunction.
Material and methods
Patients
The use of endovascular stent grafts (EVG) has been approved by the Nagoya University Ethical Committee. Operative indications were limited to patients with distal arch aneurysms involving the left subclavian artery extending to the upper middescending aorta, who were judged to have a relatively high operative risk. Informed consent was required.
There were 24 consecutive cases since February 1997. Twenty-two were men and 2 were women, with an average age of 71 (59 to 83) years. There were 22 true aneurysms (13 fusiform in type and nine saccular), one chronic type B dissection, and one penetrating aortic ulcer. Comcomitant procedures were total aortic arch replacement in two, left subclavian artery reconstruction in eight, and aortocoronary bypass grafting in four cases. Two cases were reoperations.
The average operative duration was 400 ± 75 minutes (range, 250 to 595 minutes). Circulatory arrest with RCP was utilized in 14 cases, with an average duration of 41 ± 8 minutes. Bilateral low-flow axillary arterial perfusion was carried out in 10 cases, with average time of 65 ± 17 minutes. The lower body ischemic time averaged 54 ± 27 minutes in all cases. The pump time averaged 213 ± 48 minutes, with an average cardiac ischemic time of 74 ± 27 minutes. All patients awoke within 12 hours after surgery; the average time was 4.8 ± 2.1 hours. Twenty-one (88%) patients were extubated within 24 hours. Blood transfusion was required in 10 cases (42%). Average hospital stay after surgery was 36 ± 15 days.
Methods for prevention of spinal cord dysfunction were applied as follows: pigtail catheter guidance for EVG in 19; ultra-thin woven Dacron graft in 15; use of a shorter graft with anchoring sutures in 12; flooding of the operative field with CO2 in 7; aortic unclamping in 7, and low-flow antegrade perfusion in 10. Any disorder related to the cerebrospinal system was defined as cerebrospinal dysfunction. Factors affecting cerebrospinal dysfunction were estimated by 
2 test, nonpaired t test, and univariate logistic regression analysis with StatView J5.0. A p < 0.05 was considered significant.
Operative technique for frozen elephant trunk procedure
The EVG was made with a double-linked 10-bend Z stent (50-mm length and 20% larger than the diameter of the descending aorta), and an ultra-thin woven Dacron graft (10% larger than the diameter of the descending aorta; Ubekosan, Ube, Japan). The graft and Z stent were sutured together at each bend. The Z stent alone was installed in a 12F delivery sheath (Greenfield Vena Cava Filter; Boston Science Corp., Boston, MA) with an extra-hard guidewire (Amplatz Superstiff Guidewire; Boston Science Corp.). A pigtail catheter was inserted through the groin artery into the distal aortic arch. Both the axillary arteries were exposed and anastomosed with 10-mm diameter synthetic grafts as outflow cannulation. A median sternotomy was carried out, and cardiopulmonary bypass was initiated with two-staged right atrial drainage, and both the axillary arterial perfusion and core cooling were utilized. The heart was arrested with antegrade cardioplegia with the aorta clamped. A 10-mm diameter synthetic graft was anastomosed to the aortic root. At a nasopharyngeal temperature of 20°C, low-flow perfusion (10 mL/min/kg) of both axillary arteries was initiated with clamping of the brachiocephalic artery and with ligation of the left subclavian artery. The left subclavian artery was principally reconstructed.
The anterior wall of the aortic arch was incised and the distal aortic arch was exposed. An EVG was inserted by aortotomy into the descending aorta under the pigtail catheter and guidewire guidance [4]. The Z stent was deployed just below the aneurysm. The distal edge of the Z stent was placed more than 6 cm below the aneurysm edge in order to ensure an adequate landing zone, under monitoring with transesophageal echocardiography. The graft was fixed to the aortic wall with at least two anchoring sutures of 3-0 polypropylene placed through the aortotomy. The proximal site of the graft was trimmed according to the proximal suture line surrounding the orifice of the left common carotid artery. Proximal anastomosis to the posterior wall was performed surrounding the orifice of the left common carotid artery using the inclusion technique with 3-0 polypropylene, and the aortotomy was then closed, fixing the anterior wall of the EVG. Full-flow perfusion was resumed after unclamping of the brachiocephalic artery. The graft to the left subclavian artery was anastomosed to an aortic root graft. (Fig 1)
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There was no surgical mortality, but four cases were complicated by neurologic dysfunction (17%). They were complete paraplegia in one, minor cerebral infarction along the basilar artery in one, and temporary spinal cord dysfunction in two (paresthesia of the right leg and urinary disturbance, respectively). Additional complications were disseminated intravascular coagulation in one and gastrointestinal bleeding in one.
During an average follow-up period of 29 months (range, 3 to 63 months), two cases required reoperation. One was an urgent distal aortic arch replacement due to false lumen infection in a case of type B dissection 1 year after surgery. The other patient required left thoracotomy due to perigraft leakage 3 years after surgery.
There were two late deaths. One was in a case of type B dissection due to stroke 6 months after reoperation. Another patient suffered an intraoperative stroke. He died due to another stroke 2 years after surgery.
The incidence of cerebrospinal dysfunction was evaluated for each factor. Fusiform-type aneurysms tended to be complicated by neurologic dysfunction (31%), whereas other types of aneurysms showed no incidence (p = 0.044 by 2 test). Cases involving antegrade perfusion of both axillary arteries showed no incidence of neurologic dysfunction, whereas patients using RCP showed a relatively high incidence (29%, p = 0.064 by 2 test). The incidence of cerebrospinal dysfunction was high in patients without blood transfusion (29%, p = 0.064) (Table 1).
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The frozen elephant trunk procedure is an alternative for distal aortic arch replacement. In our limited experience, it showed quicker recovery than conventional surgery and better early results, except for a relatively high risk of spinal cord dysfunction [5]. Paraplegia or paresthesia after surgery has been reported, and its incidence is higher than in nonsurgical EVG, or after conventional surgery [6, 7]. In the present study, the incidence of cerebrospinal dysfunction was 17%, including a 4% incidence of paraplegia and 9% of temporary spinal cord dysfunction.
Paraplegia occurred in a patient with a giant fusiform shape aneurysm in the distal arch. The EVG was delivered above the seventh thoracic vertebral level, but the spinal cord was injured transversely at a lower thoracic vertebral level. Incomplete or partial spinal cord injury may be characteristic of this technique. One case showed paresthesia of heat sensation only on the right anterior upper leg. The injured area was estimated to be on the right side of the posterior horn of the fourth or fifth lumbar spinal cord. Another case revealed bladder dysfunction. Only the sacral level of the spinal cord was injured. Another case suffered from cerebral infarction along the basilar artery. Debris may have entered through the left vertebral artery because of occlusion of the right vertebral artery.
The blood supply to the upper part of the spinal cord is delivered from the vertebral artery and intercostal arteries at the fourth thoracic level [8]. Interruption of the blood supply to the spinal cord with a stent graft is one of the causes of spinal cord injury, but embolization of spinal cord blood supply cannot be ruled out. Debris or air between the aneurysm wall and the stent graft may enter into the intercostal arteries and cause spinal cord embolic injury. In the most recent 10 cases, low-flow antegrade perfusion through both the axillary arteries was performed while the aorta was open. Because no incidence of cerebrospinal injury occurred in this group, we speculate that this technique may maintain blood supply to the upper part of the spinal cord and may prevent air or debris from entering into the intercostal arteries. Flooding of the operative field with carbon dioxide showed no efficacy in preventing cerebrospinal injury, so air embolization may not be related to its occurrence. It is interesting to note that spinal cord dysfunction frequently complicates fusiform-type aneurysms. This may support the possibility of embolization as an etiology because of the larger space between the aneurysm wall and the EVG in these cases.
At present, we restrict surgical indications for this procedure to patients with some comorbidity or expected high mortality with conventional surgery, because there is a lack of evidence of its long-term results and a high incidence of cerebrospinal complications. Patients with advanced age, a previous left thoracotomy, or poor pulmonary function are considered good candidates for this procedure. Otherwise, localized distal arch aneurysms can also be treated by EVG placement through the femoral artery followed by transposition of the left subclavian artery to the left common carotid artery.
The frozen elephant trunk procedure shortens postoperative recovery, and has a relatively low mortality, but the spinal cord dysfunction rate is relatively high. The mechanism of this complication and methods for its prevention should be investigated further. Long-term results of the procedure should also be clarified. The frozen elephant trunk technique is still a developing procedure, and further improvements are necessary.
References
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