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Ann Thorac Surg 2007;83:S882-S889
© 2007 The Society of Thoracic Surgeons

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Supplement

Risk Factors of Neurologic Deficit After Thoracic Aortic Endografting

^a Section of Cardiovascular and Thoracic Surgery, University of Nebraska Medical Center, Omaha, Nebraska
^b Divisions of Vascular and Endovascular Surgery, Harbor-UCLA Medical Center, Torrance, California
^c Division of Interventional Radiology, Harbor-UCLA Medical Center, Torrance, California

^_* Address correspondence to Dr Khoynezhad, Section of Cardiovascular and Thoracic Surgery, University of Nebraska Medical Center, 982315 Nebraska Medical Center, Omaha, NE 68198-2315. (Email: akhoynezhad{at}unmc.edu).

Presented at Aortic Surgery Symposium X, New York, NY, April 27–28, 2006.

	Abstract

Top Abstract Introduction Patients and Methods Results Comment References

 
BACKGROUND: Stroke and spinal cord injury (SCI) remain the most devastating complications of thoracic endovascular aortic repair (TEVAR). The risk factors associated with these complications are poorly understood. The aim of this study was to analyze the risk factors associated with neurologic deficits after TEVAR.

METHODS: From 1998 to 2005, 153 patients underwent 184 TEVARs. Computed tomography scans, angiograms, and medical records were reviewed. TEVAR was completed in all but 3 patients. The underlying pathologies included descending thoracic aortic aneurysm in 91, acute type B aortic dissection in 25, chronic type B aortic dissection in 42, aortic transection in 12, and penetrating aortic ulcer in 14.

RESULTS: Stroke developed in 8 patients, and SCI developed in another 8 patients (4 immediate, 4 delayed paraplegia/paraparesis). The procedure-associated stroke and SCI rate was 4.3% (8/184). Univariate statistical analysis revealed increased postoperative stroke with obesity, significant intraoperative blood loss, and evidence of peripheral vascular embolization/thrombosis. Aneurysmal pathology, iliac conduit, and hypogastric artery coverage were highly associated with postoperative SCI after TEVAR. Early and late mortality were 9.8% (n = 18) and 19% (n = 35) in a 16-month average period of follow-up.

CONCLUSIONS: The incidence of stroke and SCI after TEVAR was 4.3% (8/184). The risk factors associated with postoperative stroke were obesity, intraoperative blood loss, and vascular embolization. Aneurysm as an underlying pathology, the use of an iliac conduit, and coverage of the hypogastric artery were all associated with SCI. These risk factors for SCI may be markers of tenuous collateral blood supply to the spinal cord.

	Introduction

Top Abstract Introduction Patients and Methods Results Comment References

 
Thoracic endovascular aortic repair (TEVAR) has been promoted as a promising alternative to open surgical graft replacement. Proposed advantages of endograft treatment include shorter operative time, less blood loss, decreased need for general anesthesia, and shorter hospital stays [1–3]. Thoracic aortic endografting avoids morbid thoracotomy and thoracoabdominal incisions, cardiopulmonary bypass, aortic cross-clamping, and in some cases, hypothermic circulatory arrest.

A recent United States (US) multicenter trial with the Gore TAG thoracic endoprosthesis (W.L. Gore & Associates, Flagstaff, AZ) involved a selected patient population [4] of only patients with underlying aneurysm who met anatomic eligibility criteria and were candidates for open surgical repair. The results of this study were encouraging, and indeed demonstrated feasibility and durability while reducing morbidity and mortality in the selected population.

Although thoracic aortic endografting has a pattern of complications that is unique to endovascular procedures, some morbidities, such as stroke and spinal cord ischemia (SCI), are similar in both open and endovascular interventions. The aim of this study was to review the etiology and risk factors associated with stroke and SCI after TEVAR and our experience with endovascular treatment of descending aortic pathologies, and to identify risk factors of postoperative stroke and SCI.

	Patients and Methods

Top Abstract Introduction Patients and Methods Results Comment References

 
A total of 153 consecutive patients were referred to Harbor-UCLA Medical Center for TEVAR for descending thoracic aneurysms, descending thoracic dissections (Stanford type B), penetrating thoracic ulcers, and traumatic aortic transections. This included all comers, including 35 patients (19%) undergoing emergent endografting for ruptured or leaking thoracic aortas. After obtaining approval from the Institutional Review Board, the patients were offered TEVAR through a single-institution-investigator investigational device exemption protocol approved by the US Food and Drug Administration. All patients signed consent forms for the use of these investigational devices and agreed to participate in the surveillance protocols after deployment of the devices.

The inclusion/exclusion criteria for endograft treatment of thoracic aortic pathology have previously been published [5], and the same criteria were used in this patient population. A total of 184 procedures were performed from October 1998 to September 2005. This included primary and subsequent endovascular interventions. Most patients underwent endovascular repair using the Talent device (Medtronic, Minneapolis, MN). Another 37 patients were treated with the Thoracic AneuRx graft (Medtronic), and a Gore Excluder or TAG device was deployed in the remaining 2 patients.

Definitions of Neurologic Deficit
Postoperative stroke was defined as focal neurologic deficit established by an independent neurologist and correlated with acute intracranial changes on imaging studies. Similarly, SCI was reviewed by a neurologist and evaluated by magnetic resonance imaging, and was then categorized as paraplegia or paraparesis. SCI observed immediately after the index procedure was defined as immediate, and occurrence after a period of normal neurologic function was classified as delayed SCI. The lower 10 cm located proximal to the celiac axis was defined as a critical area of stent graft coverage. In most of the population, this portion of the aorta is known to be the origin of Adamkiewicz artery, which contributes significant collateral blood flow to the spinal cord [6].

The follow-up physical exam, laboratory work, and contract computed tomography (CT) imaging were performed at 1, 6, and 12 months, and yearly thereafter, for 5 years. Median follow-up was 16 ± 17 months (range, 1 to 72 months) and was complete for 92% of the patients in this series.

	Results

Top Abstract Introduction Patients and Methods Results Comment References

 
A total of 153 consecutive patients (94 men, 59 women) with a median age of 71 ± 13.7 years (range, 18 to 92 years) underwent 184 endovascular procedures. The underlying pathology was descending or transverse aortic aneurysm in 91 patients (49%), and a complicated acute or chronic type B dissection in 25 (14%) and 42 (23%) patients, respectively. Twelve (7%) patients had an aortic transection, and 14 (8%) patients were treated for a symptomatic penetrating aortic ulcer.

As a regional referral center, most of these patients were transferred by surgical colleagues from surrounding hospitals. Most were deemed to be poor surgical candidates, and 75 (41%) had had prior open-heart or major aortic surgery. The mean preoperative serum creatinine level was 1.5 ± 1.7 mg/dL. Sixteen (9%) patients had congestive heart failure, and chronic obstructive pulmonary disease was prevalent in 32 (17%).

The distribution of proximal landing zones is illustrated in Figure 1. In 23% (43/184) of the procedures, one or more of the brachiocephalic branches were covered with stent grafts. In 2 patients, an endovascular repair of the total arch was performed after transposition of the innominate and left carotid artery. In patients undergoing TEVAR in zone 1, a preoperative carotid–carotid bypass was performed. A carotid–left subclavian bypass was preformed in preparation for TEVAR in 2 patients who had either an internal mammary artery bypass or a dominant left vertebral system. All other subclavian arteries that underwent stent graft coverage were done so without clinical sequela.

View larger version (82K): [in this window] [in a new window]   Fig 1. Distribution of landing zones for thoracic endovascular aneurysm repair. Zone 0 = repair involving the innominate artery; Zone 1 = involving the left carotid artery; Zone 2 = involving the subclavian artery; Zone 3 = involving proximal one third of the descending thoracic aorta; and Zone 4 = involving the distal two thirds of the descending thoracic aorta.

Postoperative paraplegia or paraparesis occurred in 8 patients (Table 4), all of whom had aneurysm as their underlying aortic pathology. There were four immediate and four delayed cases of SCI. One patient in each group recovered completely. The remaining 6 patients (3.2%) sustained permanent SCI: 2 with paraparesis and 4 with paraplegia. Both patients with complete recoveries had cerebrospinal fluid (CSF) drains in place, and further protection was afforded to all patients by keeping the arterial system pressure high to improve cerebrospinal perfusion pressure.

Univariate analysis of variables associated with SCI was performed using methods described by Pearson and Fisher (Table 5). The chance of SCI developing was significantly higher in patients with an aortic aneurysm undergoing endografting and also in patients requiring an iliac conduit for vascular access and with an occluded or excluded hypogastric artery. The remainder of variables that were reviewed did not reveal statistical significance (Table 5).

Endoleak occurred in 36 patients (20%) during the follow-up period, and a reintervention was necessary in 23 (15%). Indications for reinterventions were type I endoleaks and enlargement of the excluded portion of the aorta. This enlargement was evaluated by increased diameter or volume on the follow-up CT scans using three-dimensional aortic reconstructions (M2S software, West Lebanon, NH). Fifteen patients had one reintervention, another 5 patients required two reinterventions, and 3 patients needed three reinterventions. Chronic or acute type B aortic dissection was the underlying pathology in 12 (52%) of 23 patients, and the remainder (48%) had aortic aneurysms. Two (9%) of the 23 patients who required a reintervention died within 30 days after the first reintervention.

Procedural associated early mortality was 9.8% (18/184) in the entire cohort, and this was similar for various aortic pathologies. The overall survival was 80% at 1 year and 67% at 5 years according to Kaplan-Meier analysis (Fig 2). When aortic-related mortality was isolated, the survival rate was 90% at 5 years (Fig 2).

View larger version (16K): [in this window] [in a new window]   Fig 2. Kaplan-Meier survival curve comparing aortic-related (solid line) and overall mortality (gray line). Tick marks indicate at least one censored patient due to the length of follow-up.

	Comment

Top Abstract Introduction Patients and Methods Results Comment References

Although the rate of stroke in the Gore TAG trial is comparable with contemporary published results, the incidence of SCI was surprisingly higher than established in aortic surgery centers [8–12]. Most experienced groups have a SCI rate of less than 5% for patients undergoing open repair of thoracic aorta, although it has been reported as high as 21% for ruptured thoracic aneurysms and acute type B dissections [8–12]. Makaroun and colleagues [4] did not review or analyze the risk factors contributing to postoperative development of stroke and SCI. The results of this study are intended to establish variables associated with postoperative neurologic deficit.

The cause of stroke after any endovascular procedure is thought to be embolic. Advancing wires and catheters in the aortic arch are known to dislodge significant amounts of atherosclerotic emboli to the brain. The initial studies on cholesterol embolization after catheterization of the aortic arch come from cardiology literature. In autopsy series, catheter-related embolization was reported in 30% of patients [13]. Recently, transcranial Doppler (TCD) ultrasound imaging has been used to evaluate the effect of guidewires and catheters in the transverse aorta after diagnostic left-heart catheterization [14]. Braekken and colleagues [14] reported cerebral microembolic signals detected by the TCD ultrasound imaging in up to 86% of the study population.

Since August 2005, we have established a protocol that uses continuous TCD ultrasound monitoring for all patients undergoing TEVAR. TCD ultrasound is an accurate monitoring tool for the detection of cerebral microemboli in a patient population with an increased risk for strokes. The TCD probe is positioned on the temporal bone window for monitoring of the middle cerebral artery. The mean blood flow velocities, pulsatility indices, and high-intensity transient signals are recorded and displayed on the screen. Although the results of our protocol are pending, TCD ultrasound has proven to be very helpful in selecting catheters, wires, and maneuvers that have a lower high-intensity transient signal rate.

Postoperative stroke has shown an association with obesity, significant intraoperative blood loss, and evidence of peripheral vascular embolization/thrombosis in this current study. The World Health Organization has defined obesity as body mass index exceeding 30 kg/m², and it is an established risk factor for developing ischemic stroke (hazard ratio, 1.72) [15]. Intraoperative blood loss and peripheral vascular complications are both markers of prolonged and complex endovascular cases. These cases involve manipulation of multiple wires, catheters, sheaths, balloons, and stent grafts close to or within the transverse aorta.

Multiple logistic regression analysis revealed no independent risk factors for developing stroke after TEVAR because the study was underpowered to detect such results. For the same reason, the known variables from clinical practice associated with a higher risk of stroke did not reveal a statistical significance. Septuagenarians and octogenarians had a higher incidence of postoperative stroke compared with patients younger than 70 years, but the statistical analysis failed to show any difference. Similarly, the following variables had higher incidence of postoperative stroke: female gender, preoperative and postoperative renal insufficiency, duration of the operation, use of general anesthesia, postoperative bleeding, and reinterventions. A multicenter study involving a greater patient population should help to further differentiate those variables and offer a more in-depth statistical computation.

The mechanism of SCI after TEVAR is not well investigated. We hypothesize that immediate SCI is related to acute ischemia of the spinal cord secondary to coverage of a large segment of intercostal vessels and other collaterals to the spinal cord blood supply, such as the subclavian and hypogastric arteries. Late SCI is thought to be secondary to a compromise of an already marginal spinal cord circulation [16]. This may be secondary to an episode of hypotension or thrombosis of covered intercostal arteries. In this study, immediate SCI occurred 4 patients and late in 4. All afflicted patients were treated with CSF drainage, increasing systemic blood pressure, and steroids after the onset of paralysis. Two patients regained normal function, 2 ambulate with walkers, and 4 remained paralyzed. Univariate analysis revealed risk factors for postoperative SCI to include aneurysm as an underlying pathology, use of iliac conduit as vascular access, and coverage/occlusion of the hypogastric artery. All three risk factors are markers of compromised spinal cord blood supply.

An iliac conduit is frequently necessary in patients with severe atherosclerosis of iliofemoral arteries. Degenerative aneurysms of the thoracic or abdominal aorta are known to have fewer numbers of patent intercostal/lumbar arteries. Many risk factors missed the threshold of statistical significance but are known to compromise the collateral blood flow to the spinal cord. These risk factors increase the incidence of SCI. Risks that are presumably a marker for more complex endovascular cases include patients having three or more stents or who require a reintervention (extended coverage of aorta), intraoperative contrast use exceeding 115 mL, and the need for general anesthesia. Septuagenarians and octogenarians also had a higher risk of postoperative SCI compared with patients younger than 70 years; however, this did not reach the conventional statistical threshold of 0.05. A multicenter trial involving more patients will further substantiate the risk factors of SCI, which are known to decrease collateral blood flow to the spinal column.

In conclusion, this study suggests that the incidence of temporary and persistent stroke and SCI after TEVAR is 4.3%, respectively. These results compare favorably with open surgical repair. Risk factors associated with postoperative stroke and SCI were identified. Although larger multicenter trials are necessary, this study confirms that TEVAR is a promising alternative to open repair. Knowledge of these variables will assist the endovascular surgeon to gauge the risk of TEVAR in patients with multiple comorbidities.

	References

Top Abstract Introduction Patients and Methods Results Comment References

 

1. White RA, Donayre CE, Walot I, et al. Endovascular exclusion of descending thoracic aortic aneurysms and chronic dissections: initial clinical results with the AneuRx device J Vasc Surg 2001;33:927-934.[Medline]
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