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Eur J Cardiothorac Surg 2002;21:5-9
© 2002 Elsevier Science NL
a Department of Cardiothoracic Surgery, St. Antonius Hospital, Nieuwegein, The Netherlands
b Department of Vascular Surgery, St. Antonius Hospital, Nieuwegein, The Netherlands
c Department of Interventional Radiology, St. Antonius Hospital, Nieuwegein, The Netherlands
d Department of Cardiology, St. Antonius Hospital, Nieuwegein, The Netherlands
Received 10 September 2001; received in revised form 26 October 2001; accepted 30 October 2001.
* Corresponding author. Tel.: +31-30-609-2047; fax: +31-30-609-2120
e-mail: rheijmen{at}hetnet.nl
| Abstract |
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Key Words: Endovascular Stent-graft Thoracic aortic aneurysm
| 1. Introduction |
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The present report describes our experience with endovascular stent-grafting in the treatment of descending thoracic aortic aneurysms using three commercially manufactured thoracic stent-graft prostheses.
| 2. Materials and methods |
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Potential candidates for endoluminal repair were evaluated preoperatively by both angiography using calibrated catheters and spiral CT scanning, and later on also duplex scanning of the iliofemoral access arteries. All our patients underwent elective repair. Five of 27 patients, however, complained of interscapular backpain at admission and were considered symptomatic at the time of intervention.
The aneurysms had divers causes, such as chronic aortic dissection (n=4, 14%), penetrating aortic ulcer (n=2, 7%), para-anastomotic pseudoaneurysm 5 years post-surgery (n=1, 4%), and a pseudoaneurysm following blunt chest trauma (n=1, 4%) [10], but the majority were due to atherosclerosis (n=20, 71%). The aneurysms were predominantly located in the proximal part of the thoracic aorta in nine patients (32%), in the central part in 11 (39%), and in the distal part in six (22%). Two (7%) patients had diffuse involvement of the entire descending thoracic aorta. Maximal aneurysmal diameter averaged 66±15 mm (15 diffuse dilations or fusiform aneurysms (54%) and 13 saccular aneurysms (46%)). In five patients (18%) with a short proximal aortic neck (<15 mm), we transposed the left subclavian artery onto the common carotid artery first as a separate procedure to lengthen the proximal anchoring zone extending as far as the origin of the left common carotid artery.
Three different commercially manufactured thoracic stent-graft prostheses were used in this study; AneuRxTM, Medtronic AVE, Cupertino, CA, USA (n=6, 21%); Talent LPSTM, Medtronic (n=9, 32%); and ExcluderTM, W.L. Gore & Associates, Flagstaff, AZ, USA (n=13, 46%). Each endoprosthesis consisted of a self-expanding nitinol stent, covered externally by a Dacron graft or internally by a PTFE graft (ExcluderTM). The type of stent-graft was selected only upon availability and surgeon's preference. A total of 41 endoprostheses were implanted in 27 patients (mean number 1.5 stent-graft per patient). In 12 patients (43%), two stent-grafts were required for aneurysm exclusion, and three stents were needed in one patient. The mean length of the stent-grafts was 140 mm (range, 60200 mm), and the mean stent-graft diameter was 35 mm (range, 2844 mm). We oversized the stents for 1020% compared with the diameter of the aortic neck on CT-scanning (mean 31 mm; range, 2440 mm) for adequate fixation.
All procedures were performed under general anesthesia by a cardiovascular surgeon in close collaboration with an interventional radiologist or cardiologist in the operating room, equipped with a movable radiolucent surgical table combined with a digital angiographic system using a ceiling-suspended C-arm (OPC 9 and DSI, Philips Medical Systems, Best, The Netherlands). The patient was placed in a supine position with the left hemithorax slightly elevated and the left arm resting beneath the posterior axillary line to enable left-anterior-oblique projections to visualize the aortic arch in its full extent. The technique of stent-graft insertion and deployment has been described in detail previously [1113]. In short, after open surgical exposure of the femoral artery, a pigtail catheter is inserted over a guidewire for the initial aortogram. Percutaneous introduction of the diagnostic catheter through the left brachial artery was used in all 11 patients (39%) with involvement of the proximal segment of the descending aorta, to aid in proper device positioning using intermittent contrast angiography. After the proximal and distal necks of the aneurysm has been marked on the monitor, a 0.035'' super-stiff guidewire (Back-up Meier, Boston Scientific, Nattick, Mass) is inserted and passed above the aneurysm site. Following the administration of 5000 IU of heparin, the stent-graft system is inserted through a transverse arteriotomy and positioned at the desired location. The femoral artery could be used for introduction of the stent-graft system in the majority of cases (n=25, 89%). In three patients, however, severe tortuosity and calcification of the ilio-femoral arteries prevented infra-inguinal introduction, and we converted to a retroperitoneal (n=2, 7%) or transabdominal approach (n=1, 4%). With the placement catheter held stationary, the sheath is gently retracted to deploy the stent-graft. The nitinol spring expands and conforms to the shape and size of the proximal and distal aortic neck. Just before the device is released, mean arterial pressure is decreased to 70 mmHg using sodium nitroprusside in order to reduce the risk of downstream migration due to arterial bloodflow. Deployment of the ExcluderTM stent-graft is achieved differently by pulling a string attached to the graft. This device opens rapidly from the middle portion to the extremities. In all stent-grafts, a polymeric balloon is inflated to obtain the optimal sealing. Finally, completion aortography is performed to verify complete aneurysm exclusion and to demonstrate free perfusion of the stent-graft (Figs. 1 and 2). All catheters are removed and the arteriotomy is closed in the usual manner. No intraoperative transesophageal echocardiography was used to verify stent-graft positioning, and no evoked spinal cord potentials were monitored intraoperatively.
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| 3. Results |
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Total length of the procedure was 94±40 min with minimal use of fluoroscopy (12±6 min) and contrast agent (108±39 ml). There was a median blood loss of 200 ml (range, 501500 ml). After a median stay in the ICU for 1 day (range, 15 days), 25 of 28 patients were discharged home within 1 week postoperatively (range 336 days).
After a median follow-up of 21 months (range, 149 months), there was one non-related late death due to a stroke 18 months postoperatively. There was no aneurysmal rupture. Maximal aneurysmal diameter either remained stable or decreased slightly over time in all but one patient with evidence of an endoleak.
3.1. Endoleaks
Intraoperative completion angiography using a pigtail catheter positioned in the thoracic aorta far above the proximal stent-graft revealed delayed contrast leakage into the aneurysmal sac in four patients (14%). Because of adequate proximal and distal sealing, all the endoleaks were considered retrograde endoleaks due to patent intercostal arteries (Type II endoleak [14]), and were treated conservatively. Of these four intraoperative endoleaks only two were noted on the CT-scan prior to discharge, in addition to two newly occurred endoleaks. CT-scanning at 3 months demonstrated one persistent endoleak with slight dilation of the aneurysm in a patient who complained of aspecific thoracic pain. Careful scrutiny of the imaging study revealed migration of the distal end of the stent-graft in the proximal direction. In another patient a newly occurred endoleak was noted at the distal attachment zone with dilation of the latter. Both endoleaks noted at 3 months follow-up (7%) were considered attachment endoleaks (Type I endoleak [14]), and were successfully treated endovascularly with insertion of a distal extension. Follow-up CT-scanning at 12 months, revealed one newly occurred endoleak in 18 evaluated patients (6%). This 81-year old man is treated conservatively to determine endoleak persistence and/or aneurysm growth. In 11 patients treated more than 2 years ago, no endoleaks have been noted on their latest annual CT-scan.
| 4. Discussion |
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Safe stent-graft placement requires distal arterial access of sufficient size, limited tortuosity of the aorta, and most importantly, a suitable aneurysm morphology. In our early experience, four patients (14%, three women) had a complicated inguinal introduction of the device, necessitating an alternative arterial access or even an emergent transabdominal iliac artery repair in one of them. In the recently reported experience of White and colleagues, seven of 26 patients (27%, five women) required femoral artery reconstruction or iliac artery grafts to repair injuries during deployment catheter passage [12]. All our potential candidates, therefore, are since then evaluated preoperatively by duplex scanning of the ilio-femoral access vessels. Angiography and spiral CT-scanning is used to determine transverse and longitudinal aneurysm diameters and their relation to the left subclavian artery and the celiac axis. For adequate fixation and safe stent-graft deployment, a sufficient length of normal aorta is necessary. In five patients (18%), we transposed the left subclavian artery onto the common carotid artery first as a separate procedure to lengthen the proximal anchoring zone. Inadvertent stent-graft placement across the origin of the left subclavian artery may result in occlusive thrombosis with left upper extremity ischemia, despite unimpeded blood flow and absence of a pressure-gradient at completion angiography [17]. Additionally, subclavian artery obstruction may lead to cerebral vascular insufficiency in compromised patients due to reversal of flow in the ipsilateral vertebral artery. The latter also contributes to the anterior spinal artery, and it is conceivable that its flow reversal may increase the risk of spinal ischemia. Furthermore, persistent flow in the left subclavian artery may result in a retrograde endoleak (Type II endoleak [14]). Alternatively, the origin of the left subclavian artery can be overstented with an uncovered proximal design of the stent-graft (Talent FreeFloTM, Medtronic). Recently, a fenestrated stent-graft with a U-shaped window at the greater curvature of the graft has been devised to prevent subclavian obstruction [18]. Both techniques however, jeopardize adequacy of proximal fixation.
Four patients (14%) were treated because of a chronic type B aortic dissection with a diameter greater than 6 cm. The dissection was limited to the thoracic aorta in all patients, meaning that all abdominal organs were perfused by the true lumen. In one patient, the stent-graft dislocated upon deployment, requiring conventional open repair in a separate procedure. In the remaining patients, successful stent-graft implantation in the proximal (n=1) and central (n=2) part of the thoracic aorta, covering the entire dilated segment, induced partial thrombosis of the false lumen within 3 months [19]. Exclusion of the false lumen in a chronically dissected aorta that extends into the abdominal aorta, however, may result in malperfusion of the abdominal organs, and represents therefore a contraindication to stent-grafting in our institution. The use of stent-grafts to cover the primary aortic intimal tear in acute type B aortic dissection, thereby obliterating the false lumen, and hence preventing subsequent dilatation, appears to be a promising new treatment [20].
Because of the absence of aortic cross-clamping and reperfusion, endovascular stent graft repair of the descending thoracic aorta may lower the incidence of spinal cord ischemia [8,11,13]. Concurrent or previous abdominal aortic repair, however, has been associated with an increased risk of paraplegia [7]. We noted no paraplegia or paraparesis, although the distal thoracic aorta was stented in eight patients (29%) with previous abdominal aortic surgery in two of them. In none of our patients, spinal vessel supply was investigated preoperatively. In the case of immediate or delayed onset paraplegia, the current design of the stent-grafts does not enable retrieval of the endoprosthesis once completely deployed. Successful reversal of paraplegia has been reported by both emergent conversion to open surgery [21], and cerebrospinal fluid (CSF) drainage [22]. Monitoring evoked spinal cord potentials during temporary interruption of the intercostal arteries by a specially designed retrievable occlusive device [23], may aid in identifying the patients at risk for spinal cord ischemia, in whom conversion to traditional open repair or prophylactic CSF drainage may be performed to avoid this complication.
The incidence of endoleaks continues to be a cause for concern. In this series, endoleaks occurred in eight of 28 cases (29%) during follow-up. In the majority of cases the endoleaks sealed spontaneously, whereas in two of them a distal extension was inserted because of dilation of the distal aortic neck and proximal migration of the distal end of the stent-graft, respectively. It has recently been shown that endovascularly excluded thoracic aortic aneurysms decrease in size similar to that found in abdominal aneurysms (about 10% yearly [8], 4 mm at 12-month follow-up) [24]. As the absolute value is quite small, it is conceivable that diameter measurement on the CT scan after midterm follow-up did not yet reveal a cumulative decrease in aneurysm size in our series. The presence of endoleaks, however, prevents substantial size decrease [8,24]. In addition, both the proximal and distal aortic neck are prone to dilation and may be associated with stent-graft migration in the tortuous aorta [24].
Recently, we have been informed about some stent-fractures that have been observed in the ExcluderTM stent-grafts, which were implanted in an early feasibility study. No clinical implications have been reported yet. However, the ExcluderTM stent-graft has not been used since in our institution, and all 13 patients (46%) will be closely evaluated at their routine follow-up.
In conclusion, our midterm data illustrate that endovascular stent-grafting for descending thoracic aortic aneurysms is technically feasible with low morbidity and mortality, and with a low conversion and reintervention rate. The occurrence of endoleaks, aortic neck dilation, and stent-graft migration remains a cause for extreme concern, and meticulous evaluation of this new technique is indicated to determine its efficacy and durability in the longer term.
| Footnotes |
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| References |
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