- Email: [email protected]
Proximal Type I Endoleak After Endovascular Abdominal Aortic Aneurysm Repair: Predictive Factors
Papers Presented to the Peripheral Vascular Surgery Society—Winter Meeting Proximal Type I Endoleak After Endovascular Abdominal Aortic Aneurysm Repair: Predictive Factors Sergio M. Sampaio, MD,1 Jean M. Panneton, MD,2,3 Geza I. Mozes, MD,1 James C. Andrews, MD,4 Thomas C. Bower, MD,1 Manju Karla, MB, BS,1 Audra A. Noel, MD,1 Kenneth J. Cherry, MD,1 Timothy Sullivan, MD,1 and Peter Gloviczki, MD,1 Rochester, Minnesota and Norfolk, Virginia
Proximal type I endoleaks after endovascular abdominal aortic aneurysm repair (EVAR) are associated with a high risk of rupture. Risk factors for developing this complication are not fully elucidated. We aimed to define preoperative predictors for proximal type I endoleak and describe its clinical outcome. From a consecutive series of 257 patients who underwent EVAR, we selected 202 who had available pre- and postoperative CT scan studies. Proximal neck diameter, length, angulation, calcification, thrombus load (thickness, percentage of neck circumference coverage, percentage of neck area occupancy), and maximum aneurysm diameter were evaluated on preoperative CT scans. All postoperative CT and duplex ultrasound scans, supplemented with angiograms in selected cases, were reviewed for the presence or absence of endoleak. Device overlap and oversizing (relative to the proximal neck) were also determined. Type I proximal endoleak rates were estimated using the Kaplan-Meier method. The associations between the variables listed above and proximal type I endoleak were evaluated by use of Cox proportional hazards models. Proximal type I endoleak occurred in eight patients, corresponding to a 3-year incidence rate of 4% (SE = 1.5%). The median follow-up was 340 days (range, 22-1954). Univariate analyses found significant associations between proximal type I endoleak and the following variables: percentage of calcified neck circumference (hazards ratio = 2.19 for a 25% increase, p = 0.019), aneurysm maximum diameter (hazards ratio = 1.98 for a 1-cm increase, p = 0.006) and proximal neck and device overlap (hazards ratio = 0.53 for a 5-mm increase, p = 0.007). The mean overlap among cases with and without type I proximal endoleak was 15.6 mm and 29.3 mm, respectively. When these variables were included in a multivariate model, all remained statistically significant. No significant association could be documented for neck thrombus-related variables. Thirty-nine (19.3%) patients had a b neck angle inferior to 120. There was a trend toward a higher incidence of proximal type I endoleaks in these patients (p = 0.057). Device oversize relative to proximal neck diameter did not affect the probability of this type of endoleak. One patient survived an emergency open repair of a ruptured aneurysm after significant expansion. Six patients underwent endovascular reinterventions (4 additional proximal cuff placements, 2 proximal angioplasties). The mean interval for
1
Division of Vascular Surgery, Mayo Clinic, Rochester, MN, USA.
2
Vascular and Transplant Specialists, Norfolk, VA, USA.
3
Eastern Virginia Medical School, Norfolk, VA, USA. Department of Radiology, Mayo Clinic, Rochester, MN, USA.
4
Correspondence to: Jean M. Panneton, 250 West Brambleton Avenue, Suite 101, Norfolk, VA 23510, USA, E-mail: [email protected]
Presented at the 13th Annual Winter Meeting of the Peripheral Vascular Surgery Society, Steamboat Springs, CO, January 31-February 2, 2004. S.M. Sampaio is a recipient of the Edward S. Rogers Clinical Research Fellowship in Vascular Surgery. Ann Vasc Surg 2004; 18: 621-628 DOI: 10.1007/s10016-004-0100-z Annals of Vascular Surgery Inc. Published online: 26 October 2004 621
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reintervention was 389 days. Distal migration (‡5 mm) was identified in four cases (50%). Proximal type I endoleak is a rare complication after EVAR, but it is associated with a high number of reinterventions and potentially serious consequences. Patients with short and heavily calcified aneurysmal necks and large aneurysms are at increased risk of proximal type I endoleaks.
INTRODUCTION Endovascular abdominal aortic aneurysm repair (EVAR) was introduced more than 10 years ago.1 Despite continuing debate over the long-term durability of this therapeutic modality, its use is becoming increasingly popular. Although being disputed as a true indicator of treatment failure,2 endoleak has traditionally been considered the major complication of EVAR.3-6 Currently accepted reporting standards7 include four types of endoleak, according to the site of origin. Type I endoleak, defined as the persistence of a perigraft channel of blood flow caused by inadequate or ineffective seal at either the proximal or distal attachment zones,7 has been considered the type having a Stronger association with negative outcomes. Its association with postoperative aneurysm expansion has been documented in multiple studies.2,8,9 Some authors claim that endoleak presence is not an indicator of any hard clinical end points,2,10,11 but the EUROSTAR registry has correlated type I endoleak with higher risks of late conversion.12,13 and ruptured.8 The prevailing opinions agree that this type of endoleak will have serious clinical consequences, even if secondary sealing is achieved.14 The objective of this study is to evaluate the impact of preoperative anatomic characteristics on the incidence rate of proximal type I endoleak.
METHODS From a consecutive series of 257 patients who underwent endovascular repair of their abdominal aortic aneurysms, we selected 202 patients whose records included the preoperative and at least one postoperative computed tomography (CT) scan. Mean age was 76.1 (range, 46.9-97.3) years. Twenty-four (11.9%) patients were women and 178 (88.1%) were men. Seven devices were used: TalentTM (Medtronic, Sunrise, FL), (n = 1 [0.4%]), VanguardTM (Boston Scientific, Natick, MA), (n = 5 [2%]), ExcluderTM (W.L. Gore and Associates, Flagstaff, AZ), (n = 3 [1.5%]), EndologixTM (Endologix Inc., Irvine, CA), (n = 6 [3%]), EVTTM (Endo vascular Technologies,
Menlo Park, CA), (n = 2 [1%]), AncureTM (Guidant, Menlo Park, CA), (n = 38 [18.9%]), and AneuRxTM (Medtronic, Santa Rosa, CA), (n = 147 [72.8%]). CT scans were obtained using GE Lightspeed scanners (General Electric, Milwaukee, WI). Noncontrast images, 5 mm thick with 5-mm spacing, were obtained through the abdomen and pelvis. Contrast-enhanced images were then obtained with a single breath-hold during the injection of 120 mL of nonionic contrast at 4 mL/sec. Helical acquisition was performed with reconstruction of the images into 2.5-mm slices every 2.5-mm. Several anatomic characteristics of the proximal neck were evaluated with the aid of electronic calipers available at the CT workstation. Proximal neck angle was measured on spatially corrected three-dimension CT scan reconstructions. The b angle, the angle between the flow axis of the infrarenal neck and the body of the aneurysm, was classified at two levels: > 120 and £ 120.15 A neck was considered reverse tapered when its distal diameter was ‡3 mm wider than the proximal (infrarenal) diameter. Neck length was evaluated by calculating the difference in CT table position (in mm) between the lowest renal artery and the beginning of the aneurysm sac as recorded on the CT image). All of the following anatomic variables were measured at mid-neck level (half-way between these two levels), which was felt to best represent the neck characteristics at the planned deployment site. Neck diameter was measured adventitia to adventitia, using the minor axis of the elliptical cross-section to avoid angulation-related overestimation.15 Neck calcification was evaluated as percentage of calcified neck wall. Neck thrombus load was measured in three different ways: maximum thrombus thickness, percentage of neck wall lined by thrombus, and percentage of cross-sectional area occupied by thrombus. Device proximal oversizing was defined by the following formula: (device proximal diameter – proximal neck diameter) / proximal neck diameter. Device proximal overlap was defined according to the following formula: (proximal neck length) – (lowest renal to proximal end of device distance), in an attempt to quantify the length of device actually landed on the aortic region preoperatively read as ‘‘neck.’’
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Proximal type I endoleak after EVAR 623
Aneurysm maximal diameter was also evaluated form adventitia to adventitia, using the minor axis from the cross-sectional elipse.15 Percentage of sac cross-sectional area occupied by thrombus was measured at the maximal diameter level. The outcome of interest was defined as the occurrence of a type I endoleak arising from the proximal attachment site. Its presence was evaluated in all available postoperative CT scans. This routine evaluation was supplemented with angiograms in selected cases, when the exact origin of the endoleak could not be documented with absolute certainty solely on the basis of the CT images. Cases where the endoleak had multiple origins, if one of them was the proximal attachment site, were considered to have the outcome of interest. Statistics Proximal type I endoleak rate was estimated with the Kaplan-Meier method. Time of event was ascribed to the date of the first postoperative CT scan with evidence of proximal type I endoleak. Associations between all of the previously mentioned variables and proximal type I endoleak were tested using Cox proportional hazards models. Variables with significant associations in the univariate analysis were subsequently included in a multivariate model. A p value < 0.05 was used to determine statistical significance.
RESULTS The 202 patients were followed for a median time of 340 days, with a range of 22 to 1954 days. Proximal type I endoleaks occurred in eight patients, corresponding to an estimated 3-year rate of 4% (SE = 1.5%) (Fig. 1). The median time of endoleak detection was 11 days. The earliest type I endoleak was detected on the first postoperative day, and the latest one 1239 days after the procedure. In three of these eight patients (37.5%), who ultimately went on to develop an attachment site endoleak during follow-up, the EVAR procedure was complicated by an intraoperative proximal type I endoleak. Two were resolved by intraoperative angioplasty of the proximal landing zone and in one patient an additional cuff was placed. None of the eight patients left the operative room with a visible proximal type I endoleak on completion angiogram. In one patient the aneurysm increased in diameter (12.4 mm) and ruptured 155 days after
Fig. 1. Freedom from proximal type I endoleak: 96% at 3 years, Kaplan-Meier estimate. Dashed line, standard error ‡10%.
EVAR. This patient underwent open repair and survived. Six other patients underwent reinterventions to address proximal type I endoleaks. Four of them were managed by additional proximal cuff placement (Fig. 2) and the remaining two by percutaneous balloon angioplasty of the proximal landing zone. All of the reinterventions resulted in technical success, with no residual proximal type I endoleak identifiable up to the last follow-up. Mean post-reintervention follow-up was 6.36 months (range, 0-19.2 months). One of the patients had no reintervention, despite the known proximal type I endoleak. This patient was a 91-year-old male with significant medical comorbidities, unsuitable anatomy for an additional cuff placement, and no detectable aneurysm enlargement. A decision was made to pursue an expectant attitude. Caudad migration of the endograft (‡5 mm) was detected in four (50%) patients with proximal type I endoleak. The main clinical features of all eight cases are summarized in Table I. Forty-three (21.3%) necks had a reverse tapered shape. This characteristic was not associated with the outcome of interest. Thirty-nine (19.3%) patients had a b neck angle inferior to 120. There was a trend toward a higher incidence of proximal type I endoleaks in these patients (p = 0.057). In most necks a relatively small proportion of the wall was calcified. The median proportion of calcifica-
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Fig. 2. Fluoroscopic images of proximal type I endoleak (arrow, left); additional cuff placement (middle); and final angiogram (right).
Table I. Clinical course of 8 patients with proximal type I endoleak Age
Intraoperative proximal type I endoleak
Time interval after EVAR (days)
Aneurysm expansiona
Device migrationb
Reintervention
80 65 64 91 74 76 80 91
Yes No No No Yes No Yes No
1239 253 155 1 1 1 1 21
No No Yes No No No No No
Yes Yes No No Yes Yes No No
Proximal cuff Proximal cuff Open repair after rupture Proximal angioplasty Proximal cuff Proximal cuff Proximal angioplasty —
a
Diameter increase ‡5 mm, relative to preoperative diameter. Device caudad displacement ‡5 mm, relative to first postoperative CT scan.
b
tion was 16.8%, and 90% of the patients had less than half of the wall calcified. Neck calcification was associated with an increased risk of proximal type I endoleak. With a 25% increase in the percentage of neck calcification, the probability of developing this complication increased 2.2 times (p = 0.019). Neck thrombus was relatively scarce. Sixty-one patients (29.5%) had no identifiable thrombus and in 50% less than one-third of the cross-sectional area was occupied by thrombus. In half of the patients <45% of the neck wall perimeter was lined by thrombus. Among patients with neck thrombus, the mean thickness was 4.6 mm and it covered on average 63.7% of the neck wall. None of the neck thrombus-related variables was significantly associated with the risk of developing a proximal type I endoleak.
Mean aneurysm diameter was 54.7 mm (range: 40-96 mm). Larger aneurysms were at a higher risk of developing the outcome of interest: for each additional centimeter, the risk of a proximal type I endoleak increased 1.98 times (p = 0.006). Aneurysms with more thrombus within their sac showed a trend toward decreased risk of this type of endoleak. For a 10% increase in the thrombosed cross-sectional area, this risk decreased by 0.74 (p = 0.053). The degree of proximal oversizing of the device relative to the neck diameter was a function of the neck diameter itself. Wider necks were less oversized. For each additional millimeter in diameter, the oversizing decreased on average 3.3% (linear regression, p < 0.0001; correlation coefficient = -0.83). The diameter difference between device and proximal neck (expressed as percentage of neck
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diameter) was not associated with the probability of proximal type I endoleak. Overlapping of the device on the proximal neck was almost perfectly correlated with the neck length: for each additional millimeter in neck length, the overlapped distance increased 0.97 mm on average (linar regression, p < 0.0001; correlation coefficient = 0.99). Increasing neck length (p = 0.01) and overlapped length (p = 0.007) were associated with lower risks of proximal type I endoleak. For each additional 5 mm of overlapping, the chance of developing this type of endoleak decreased 0.5 times. The strengths and significance of associations between all the above characteristics and the occurrence of a proximal type I endoleak are summarized in Table II. After adjusting for each variable in a multivariate Cox proportional hazards model, all of the univariately significant associations remained significant. The model, whose overall significance reached a p value equal to 0.0001, is summarized in Table III.
DISCUSSION Data on the incidence of type I proximal endoleak are not especially abundant. Most reports tend to mention overall rates of type I endoleaks arising from both proximal and distal attachment sites or of both type I and III endoleaks. This tendency probably results from the conviction that these types of endoleak imply similar negative prognostic consequences. Nevertheless, proximal type I endoleaks have been reported with frequencies ranging from 016 to 2.6%.17 Both these studies, however, did not report estimated probabilities based on the number of patients at risk and respective follow-up time, making comparisons difficult with the present study’s estimated incidence (4% by 3 years in this study), which was calculated using the KaplanMeier method. The risk factors involved in the development of a proximal type I endoleak are certainly specific for this location, and there is some evidence that their clinical consequences might also differ from distal type I endoleaks. In fact, proximal type I endoleaks have been described as independent risk factors for post-EVAR rupture,13 whereas the same association was not demonstrated for endoleaks arising from distal attachment sites. For these reasons we were motivated to focus on isolated proximal type I endoleaks. Our study confirms that these are relatively rare events. Interestingly, three of the patients who had a postoperative proximal type I endoleak had already experienced the same complication intraopera-
Proximal type I endoleak after EVAR 625
tively. Presumably, the same hostile characteristics that did not allow achievement of an effective proximal seal continued to exert their deleterious action postoperatively, causing recurrence of the problem. As described elsewhere, the intraoperative occurrence of a proximal type I endoleak, even if corrected (and thus not visible at the last completion angiogran study), is associated with an increased risk of this complication during postoperative follow-up (Sampio et al., submitted for publication). The number of events (n = 8) is obviously too small for any statistically sound inference about the clinical consequences of this type of endoleak. Nevertheless, it is worth noting that one of the patients (12.5%) progressed to aneurysm expansion and rupture. This isolated instance in concurrence with most reports on the special significance of this complication.2,8,13 Attempts to classify the aneurysm proximal neck in terms of its shape have been dismissed in the currently recommended reporting standards as oversimplistic and of reduced applicability.15 We tried to use objective criteria in defining a reverse tapered neck. Intuitively, such necks would result in the ‘‘squeezing’’ of the device into the aneurysm sac. As in a previous study,18 our results did not provide any evidence to support this hypothesis. Angulated necks have been associated with poor outcome after EVAR.19 Specifically, type I endoleaks have been found more frequently in patients with proximal neck beta angles below 12019 or, conversely, patients with type I endoleaks have more acute proximal neck angles (17, mean).18 Petrik and Moore20 did not confirm this difference, but their study did not include patients with neck angles below 120, limiting the value of any comparisons. Despite finding a clear trend, our study failed to reach a significant association for this variable. Curiously, the only rupture occurred in a highly angulated neck. Thrombus in the aneurysm neck was one of the exclusion criteria for EVAR clinical trials. This exclusion was based on the assumption that neck thrombus posed an additional threat of three complications: proximal type I endoleak, device migration, and renal or distal embolization. As for type I endoleaks, the rationale for this association rests on two possible mechanisms of action: an immediate effect preventing a watertight seal, and deferred thrombus lysis, allowing for sac reperfusion and repressurization. These have been challenged by Gitlitz et al.,21 who found no early or late endoleaks (mean follow-up = 23 months; n = 19) in patients with more than three-fourths of the
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Table II. Impact of preoperative characteristics on proximal type I endoleak cumulative incidence rate by univariate Cox proportional hazards models analysis
Preoperative characteristic
Reverse tapered neck Angulated neck (>60) Percent of calcified neck wall Percent of thrombus-lined neck wall Neck thrombus thickness Percent of thrombosed neck cross-sectional area Neck length Device and neck overlap Device and neck oversize Aneurysm diameter Percent of thrombosed sac cross-sectional area
Hazards ratio of developing proximal type I endoleak
Increment
1.25 2.01 2.19 0.99
Yes or no Yes or no 25% 25%
0.48-2.71 0.98-4.14 1.09-4.17 0.64-1.57
0.6 0.057 0.019 0.996
0.96 0.96
1 mm 10%
0.79-1.16 0.66-1.4
0.644 0.849
0.61 0.53 0.82 1.98 0.74
5 mm 5 mm 10% 1 cm 10%
0.368-0.9 0.34-0.86 0-1.59 1.22-3.25 0.53-1
0.01 0.007 0.555 0.006 0.053
Hazards ratio 95% CI
p
CI, confidence interval.
Table III. Impact of preoperative characteristics on proximal type I endoleak cumulative incidence rate by multivariate Cox proportional hazards models analysis Preoperative characteristic
Hazards ratio of developing a proximal type I endoleak
Increment
Hazards ratio 95% CI
p
Overall model Percent of calcified neck wall Device and neck overlap Aneurysm maximal diameter
— 2.4 0.45 1.9
— 25% 5 mm 1 cm
— 1.19-4.9 0.26-0.81 1.07-3.39
0.001 0.01 0.008 0.03
CI, confidence interval.
neck wall lined with thrombus. One could argue that this way of classifying neck thrombus is too crude to detect any true effect, especially when it results in an ‘‘exposed’’ cohort of only 19 patients. In the present study, neck thrombus was evaluated using three different measurements, all of them in continuous instead of categorical scales. No impact of thrombus could be demonstrated, but some caution should be used in interpreting these results, because CT images read as thrombus might truly correspond to thick, noncalcified atheroma. Such cases might have been systematically wrongly classified on all studies (as thrombus-lined necks), diluting any potential effect of true neck thrombus. Nevertheless, aortic neck filling defects detected on CT scans do not seem to pose an additional risk of developing proximal type I endoleaks. One should also note that while a seal may be achieved when the endograft is implanted into thrombus proximally, this situation may lead to endotension, graft migration, and rupture, as noted by White et al.22
The potential relevance of endograft oversizing in the development of a proximal type I endoleak is related to endograft migration: excessively oversized grafts would be at a higher risk of being ‘‘squeezed’’ out of the aortic neck, especially devices without hooks or barbs. No reports exists on the direct impact of oversize on endoleak occurrence. Several studies23-26 have documented an association between neck dilation and graft oversizing, but conflicting reports also exist.27 Neck dilation, in turn, was associated with increased risk of device migration.23,25 Interestingly, no direct association was ever demonstrated between oversizing and device migration. Whether this simply reflects a lack of follow-up time to detect enough migration events remains to be elucidated. Device migration was clearly an implicated mechanism in at least half of the endoleak cases in our series, but no significant impact of oversizing could be documented. Calcification of the proximal neck could be implicated in sealing failure, through two potential
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mechanisms. Heavily calcified necks might be less flexible and more irregular, hence less able to fit closely around the endograft and achieve a hemostatic seal. Large surfaces of calcified plaque might constitute a more ‘‘slippery’’ wall, upon which the endograft could easily migrate. Calcification has only been proven under experimental conditions on cadaveric aortas to constitute a risk factor for endograft migration.28 Our results indicate that calcification may be associated with the probability of proximal type I endoleaks. Short necks have been proven to affect the incidence of intraoperative complications.29 The association between neck length and achievement of an effective proximal seal is intuitive. Either by providing a larger area of contact to obtain a hemostatic seal or by increasing the friction forces, making endograft displacement less likely, a long neck is generally seen as an advantageous feature. This is true to the extent that a longer neck actually means a longer distance of overlap, as was the case in our study. Neck length and neck and device overlap were closely correlated. This is an expected consequence of the adopted technique of placing the endograft immediately below the lowest renal artery, taking advantage of the total available proximal landing zone. These considerations might seem logical, but confirming clinical data are absent. Cao et al.23 did not find any significance for neck length in the genesis of device migration, but they evaluated this variable in a categorical fashion, classifying patients as having or not having necks shorter than 10 mm. Conners et al.25 also failed to show any effect of the degree of overlap, but they evaluated its impact in a non-time-dependent fashion, by comparing means between migrators and nonmigrators, not accounting for different lengths of follow-up or censoring. Greenberg et al.30 specifically tested the impact of short necks on endoleak rates, without any significant association. However, their total sample size was only 55, they defined their outcome of interest as any type of endoleak, and they performed their tests without taking follow-up duration or censoring into account. Our study found a highly significant impact of the length of the overlapped zone and the risk of a proximal type I endoleak. Of all the tested variables, this one achieved the highest level of significance and was one of the strongest factors. Our results are in concurrence with a previous work that identified this variable as a key feature in endograft migration in an experimental setting.28 Larger aneurysms have been reported to be at increased risk of developing a type I endoleak.31,32
Proximal type I endoleak after EVAR 627
Debate has ensued about the true meaning of such observations, since they might simply result from the demonstrable inverse correlation between aneurysm diameter and neck length.29,31 This correlation existed in our study, albeit weak and barely significant (correlation coefficient, –0.14; p = 0.046). Moreover, when included together in a multivariate Cox proportional hazards model, both variables remained independent predictors of proximal type I endoleak. The rationale for the deleterious effect of large aneurysm diameter could reside in the lack of support around the main body of the device, which increase its positional stability and decrease the friction forces that presumably help keep the endograft in place. This hypothesis concurs with the trend that our study found for an increased risk of proximal type I endoleaks in patients with less thrombus in their aneurysms: more empty space inside the sac increases the risk of a proximal seal failure. We believe the main weakness of this study lies in the low number of events detected. However, if this increased the risk of a type II error (as might have been the case in evaluation of the impact of neck angulation), it reinforces the significance of the demonstrable associations. Therefore, although we believe special caution should be used in interpretation of this study’s negative results, we are convinced that length of proximal fixation, neck calcification, and aneurysm size are meaningful independent risk factors for development a seal failure at the proximal attachment site.
CONCLUSIONS Proximal type I endoleak is a rare complication after EVAR, but it is associated with a high number of reinterventions and potentially serious consequences. Patients with large aneurysms and shorter and more calcified aneurysmal necks are at increased risk of such events. REFERENCES 1. Parodi JC, Palmaz JC, Barone HD. Transfemoral intraluminal graft implantation for abdominal aortic aneurysm. Ann. Vasc. Surg. 1991;5:491-499. 2. Zarins CK, White RA, Hodgson KJ, Schwarten D, Fogarty TJ. Endoleak as a predictor of outcome after endovascular aneurysm repair: AneuRx multicenter clinical trial. J. Vasc. Surg. 2000;32:90-107. 3. Harris PL. The highs and lows of endovascular aneurysm repair: the first two years of the EUROSTAR registry. Ann. R. Coll. Surg. Engl. 1999;81:161-165. 4. Shurink GWH, Arts NJM, Vanbockel JH. Endoleak after stent-graft treatment of abdominal aortic aneurysm. Br. J. Surg. 1999;86:581-587.
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dovascular abdominal aortic aneurysm repair. J. Vasc. Surg. 2002;35:482-486. Petrik PV, Moore WS. Endoleaks following endovascular repair of abdominal aortic aneurysm: the predictive value of preoperative anatomic factors—a review 100 cases. J. Vasc. Surg. 2000;3:739-744. Gitlitz DB, Ramaswamy G, Kaplan D, Hollier LH, Marin ML. Endovascular stent grafting in the presence of aortic neck filling defects: early clinical experience. J. Vasc. Surg. 2001; 3:340-334. White GH, May J, Petrasek P, Waugh R, Stephen MS, Harris J. Endotension: an explanation for continued AAA growth after successful endoluminal repair. J. Endovasc. Surg. 1999;4:308-315. Cao P, Verzini F, Zannetti S, et al. Device migration after endoluminal abdominal aortic aneurysm repair: analysis of 113 cases with a minimum follow-up period of 2 years. J. Vasc. Surg. 2002;31:229-235. Prinssen M, Wever JJ, Willem P, Mali M, Eikelboom BC, Blankensteijn JD. Concerns for the durability of the proximal abdominal aortic aneurysm endograft fixation from a 2-year and 3-year longitudinal computed tomography angiography study. J. Vasc. Surg. 2001;33:S64S69. Conners MS, Sternbergh C, Carter G, Tonnessan BH, Yoselevitz M, Money SR. Endograft migration one to four years after endovascular abdominal aortic aneurysm repair with the AneuRx device: a cautionary note. J. Vasc. Surg. 2002;36:476-484. Badran MF, Gould DA, Raza I, et al. Aneurysm neck diameter after endovascular repair of abdominal aortic aneurysms. J. Vasc. Interv. Radiol. 2002;13:887-892. Matsumura JS, Chaikof EL. Continued expansion of aortic necks after endovascular repair of abdominal aortic aneurysm. J. Vasc. Surg. 1998;28:422-431. Lambert AW, Williams DJ, Budd JS, Horrocks M. Experimental assessment of proximal stent-graft fixation in human cadaveric infrarenal aortas. Eur. J. Vasc. Endovasc. Surg. 1998;7:60-65. Hovsepian DM, Hein AN, Pilgram TK, et al. Endovascular abdominal aortic aneurysm repair in 144 patients: correlation of aneurysm size, proximal aortic neck length and procedure-related complications. J. Vasc. Interv. Radiol. 2001;12:1373-1382. Greenberg R, Fairman R, Srivastava , Criado F, Green R. Endovascular grafting in patients with short proximal necks: an analysis of short-term results. Cardiovasc. Surg. 2000; 8:350-354. Rockman CB, Lamparello PJ, Adelman MA, et al. Aneurysm morphology as a predictor of endoleak following endovascular aortic aneurysm repair: do smaller aneurysm have better outcomes? Ann. Vasc. Surg. 2002;16:644-651. Ouriel K, Srivastava SD, Sarac TP, et al. Disparate outcome after endovascular treatment of small versus large abdominal aortic aneurysm. J. Vasc. Surg. 2003;37:1206-1212.
Proximal type I endoleaks after endovascular abdominal aortic aneurysm repair (EVAR) are associated with a high risk of rupture. Risk factors for developing this complication are not fully elucidated. We aimed to define preoperative predictors for proximal type I endoleak and describe its clinical outcome. From a consecutive series of 257 patients who underwent EVAR, we selected 202 who had available pre- and postoperative CT scan studies. Proximal neck diameter, length, angulation, calcification, thrombus load (thickness, percentage of neck circumference coverage, percentage of neck area occupancy), and maximum aneurysm diameter were evaluated on preoperative CT scans. All postoperative CT and duplex ultrasound scans, supplemented with angiograms in selected cases, were reviewed for the presence or absence of endoleak. Device overlap and oversizing (relative to the proximal neck) were also determined. Type I proximal endoleak rates were estimated using the Kaplan-Meier method. The associations between the variables listed above and proximal type I endoleak were evaluated by use of Cox proportional hazards models. Proximal type I endoleak occurred in eight patients, corresponding to a 3-year incidence rate of 4% (SE = 1.5%). The median follow-up was 340 days (range, 22-1954). Univariate analyses found significant associations between proximal type I endoleak and the following variables: percentage of calcified neck circumference (hazards ratio = 2.19 for a 25% increase, p = 0.019), aneurysm maximum diameter (hazards ratio = 1.98 for a 1-cm increase, p = 0.006) and proximal neck and device overlap (hazards ratio = 0.53 for a 5-mm increase, p = 0.007). The mean overlap among cases with and without type I proximal endoleak was 15.6 mm and 29.3 mm, respectively. When these variables were included in a multivariate model, all remained statistically significant. No significant association could be documented for neck thrombus-related variables. Thirty-nine (19.3%) patients had a b neck angle inferior to 120. There was a trend toward a higher incidence of proximal type I endoleaks in these patients (p = 0.057). Device oversize relative to proximal neck diameter did not affect the probability of this type of endoleak. One patient survived an emergency open repair of a ruptured aneurysm after significant expansion. Six patients underwent endovascular reinterventions (4 additional proximal cuff placements, 2 proximal angioplasties). The mean interval for
1
Division of Vascular Surgery, Mayo Clinic, Rochester, MN, USA.
2
Vascular and Transplant Specialists, Norfolk, VA, USA.
3
Eastern Virginia Medical School, Norfolk, VA, USA. Department of Radiology, Mayo Clinic, Rochester, MN, USA.
4
Correspondence to: Jean M. Panneton, 250 West Brambleton Avenue, Suite 101, Norfolk, VA 23510, USA, E-mail: [email protected]
Presented at the 13th Annual Winter Meeting of the Peripheral Vascular Surgery Society, Steamboat Springs, CO, January 31-February 2, 2004. S.M. Sampaio is a recipient of the Edward S. Rogers Clinical Research Fellowship in Vascular Surgery. Ann Vasc Surg 2004; 18: 621-628 DOI: 10.1007/s10016-004-0100-z Annals of Vascular Surgery Inc. Published online: 26 October 2004 621
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reintervention was 389 days. Distal migration (‡5 mm) was identified in four cases (50%). Proximal type I endoleak is a rare complication after EVAR, but it is associated with a high number of reinterventions and potentially serious consequences. Patients with short and heavily calcified aneurysmal necks and large aneurysms are at increased risk of proximal type I endoleaks.
INTRODUCTION Endovascular abdominal aortic aneurysm repair (EVAR) was introduced more than 10 years ago.1 Despite continuing debate over the long-term durability of this therapeutic modality, its use is becoming increasingly popular. Although being disputed as a true indicator of treatment failure,2 endoleak has traditionally been considered the major complication of EVAR.3-6 Currently accepted reporting standards7 include four types of endoleak, according to the site of origin. Type I endoleak, defined as the persistence of a perigraft channel of blood flow caused by inadequate or ineffective seal at either the proximal or distal attachment zones,7 has been considered the type having a Stronger association with negative outcomes. Its association with postoperative aneurysm expansion has been documented in multiple studies.2,8,9 Some authors claim that endoleak presence is not an indicator of any hard clinical end points,2,10,11 but the EUROSTAR registry has correlated type I endoleak with higher risks of late conversion.12,13 and ruptured.8 The prevailing opinions agree that this type of endoleak will have serious clinical consequences, even if secondary sealing is achieved.14 The objective of this study is to evaluate the impact of preoperative anatomic characteristics on the incidence rate of proximal type I endoleak.
METHODS From a consecutive series of 257 patients who underwent endovascular repair of their abdominal aortic aneurysms, we selected 202 patients whose records included the preoperative and at least one postoperative computed tomography (CT) scan. Mean age was 76.1 (range, 46.9-97.3) years. Twenty-four (11.9%) patients were women and 178 (88.1%) were men. Seven devices were used: TalentTM (Medtronic, Sunrise, FL), (n = 1 [0.4%]), VanguardTM (Boston Scientific, Natick, MA), (n = 5 [2%]), ExcluderTM (W.L. Gore and Associates, Flagstaff, AZ), (n = 3 [1.5%]), EndologixTM (Endologix Inc., Irvine, CA), (n = 6 [3%]), EVTTM (Endo vascular Technologies,
Menlo Park, CA), (n = 2 [1%]), AncureTM (Guidant, Menlo Park, CA), (n = 38 [18.9%]), and AneuRxTM (Medtronic, Santa Rosa, CA), (n = 147 [72.8%]). CT scans were obtained using GE Lightspeed scanners (General Electric, Milwaukee, WI). Noncontrast images, 5 mm thick with 5-mm spacing, were obtained through the abdomen and pelvis. Contrast-enhanced images were then obtained with a single breath-hold during the injection of 120 mL of nonionic contrast at 4 mL/sec. Helical acquisition was performed with reconstruction of the images into 2.5-mm slices every 2.5-mm. Several anatomic characteristics of the proximal neck were evaluated with the aid of electronic calipers available at the CT workstation. Proximal neck angle was measured on spatially corrected three-dimension CT scan reconstructions. The b angle, the angle between the flow axis of the infrarenal neck and the body of the aneurysm, was classified at two levels: > 120 and £ 120.15 A neck was considered reverse tapered when its distal diameter was ‡3 mm wider than the proximal (infrarenal) diameter. Neck length was evaluated by calculating the difference in CT table position (in mm) between the lowest renal artery and the beginning of the aneurysm sac as recorded on the CT image). All of the following anatomic variables were measured at mid-neck level (half-way between these two levels), which was felt to best represent the neck characteristics at the planned deployment site. Neck diameter was measured adventitia to adventitia, using the minor axis of the elliptical cross-section to avoid angulation-related overestimation.15 Neck calcification was evaluated as percentage of calcified neck wall. Neck thrombus load was measured in three different ways: maximum thrombus thickness, percentage of neck wall lined by thrombus, and percentage of cross-sectional area occupied by thrombus. Device proximal oversizing was defined by the following formula: (device proximal diameter – proximal neck diameter) / proximal neck diameter. Device proximal overlap was defined according to the following formula: (proximal neck length) – (lowest renal to proximal end of device distance), in an attempt to quantify the length of device actually landed on the aortic region preoperatively read as ‘‘neck.’’
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Proximal type I endoleak after EVAR 623
Aneurysm maximal diameter was also evaluated form adventitia to adventitia, using the minor axis from the cross-sectional elipse.15 Percentage of sac cross-sectional area occupied by thrombus was measured at the maximal diameter level. The outcome of interest was defined as the occurrence of a type I endoleak arising from the proximal attachment site. Its presence was evaluated in all available postoperative CT scans. This routine evaluation was supplemented with angiograms in selected cases, when the exact origin of the endoleak could not be documented with absolute certainty solely on the basis of the CT images. Cases where the endoleak had multiple origins, if one of them was the proximal attachment site, were considered to have the outcome of interest. Statistics Proximal type I endoleak rate was estimated with the Kaplan-Meier method. Time of event was ascribed to the date of the first postoperative CT scan with evidence of proximal type I endoleak. Associations between all of the previously mentioned variables and proximal type I endoleak were tested using Cox proportional hazards models. Variables with significant associations in the univariate analysis were subsequently included in a multivariate model. A p value < 0.05 was used to determine statistical significance.
RESULTS The 202 patients were followed for a median time of 340 days, with a range of 22 to 1954 days. Proximal type I endoleaks occurred in eight patients, corresponding to an estimated 3-year rate of 4% (SE = 1.5%) (Fig. 1). The median time of endoleak detection was 11 days. The earliest type I endoleak was detected on the first postoperative day, and the latest one 1239 days after the procedure. In three of these eight patients (37.5%), who ultimately went on to develop an attachment site endoleak during follow-up, the EVAR procedure was complicated by an intraoperative proximal type I endoleak. Two were resolved by intraoperative angioplasty of the proximal landing zone and in one patient an additional cuff was placed. None of the eight patients left the operative room with a visible proximal type I endoleak on completion angiogram. In one patient the aneurysm increased in diameter (12.4 mm) and ruptured 155 days after
Fig. 1. Freedom from proximal type I endoleak: 96% at 3 years, Kaplan-Meier estimate. Dashed line, standard error ‡10%.
EVAR. This patient underwent open repair and survived. Six other patients underwent reinterventions to address proximal type I endoleaks. Four of them were managed by additional proximal cuff placement (Fig. 2) and the remaining two by percutaneous balloon angioplasty of the proximal landing zone. All of the reinterventions resulted in technical success, with no residual proximal type I endoleak identifiable up to the last follow-up. Mean post-reintervention follow-up was 6.36 months (range, 0-19.2 months). One of the patients had no reintervention, despite the known proximal type I endoleak. This patient was a 91-year-old male with significant medical comorbidities, unsuitable anatomy for an additional cuff placement, and no detectable aneurysm enlargement. A decision was made to pursue an expectant attitude. Caudad migration of the endograft (‡5 mm) was detected in four (50%) patients with proximal type I endoleak. The main clinical features of all eight cases are summarized in Table I. Forty-three (21.3%) necks had a reverse tapered shape. This characteristic was not associated with the outcome of interest. Thirty-nine (19.3%) patients had a b neck angle inferior to 120. There was a trend toward a higher incidence of proximal type I endoleaks in these patients (p = 0.057). In most necks a relatively small proportion of the wall was calcified. The median proportion of calcifica-
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Fig. 2. Fluoroscopic images of proximal type I endoleak (arrow, left); additional cuff placement (middle); and final angiogram (right).
Table I. Clinical course of 8 patients with proximal type I endoleak Age
Intraoperative proximal type I endoleak
Time interval after EVAR (days)
Aneurysm expansiona
Device migrationb
Reintervention
80 65 64 91 74 76 80 91
Yes No No No Yes No Yes No
1239 253 155 1 1 1 1 21
No No Yes No No No No No
Yes Yes No No Yes Yes No No
Proximal cuff Proximal cuff Open repair after rupture Proximal angioplasty Proximal cuff Proximal cuff Proximal angioplasty —
a
Diameter increase ‡5 mm, relative to preoperative diameter. Device caudad displacement ‡5 mm, relative to first postoperative CT scan.
b
tion was 16.8%, and 90% of the patients had less than half of the wall calcified. Neck calcification was associated with an increased risk of proximal type I endoleak. With a 25% increase in the percentage of neck calcification, the probability of developing this complication increased 2.2 times (p = 0.019). Neck thrombus was relatively scarce. Sixty-one patients (29.5%) had no identifiable thrombus and in 50% less than one-third of the cross-sectional area was occupied by thrombus. In half of the patients <45% of the neck wall perimeter was lined by thrombus. Among patients with neck thrombus, the mean thickness was 4.6 mm and it covered on average 63.7% of the neck wall. None of the neck thrombus-related variables was significantly associated with the risk of developing a proximal type I endoleak.
Mean aneurysm diameter was 54.7 mm (range: 40-96 mm). Larger aneurysms were at a higher risk of developing the outcome of interest: for each additional centimeter, the risk of a proximal type I endoleak increased 1.98 times (p = 0.006). Aneurysms with more thrombus within their sac showed a trend toward decreased risk of this type of endoleak. For a 10% increase in the thrombosed cross-sectional area, this risk decreased by 0.74 (p = 0.053). The degree of proximal oversizing of the device relative to the neck diameter was a function of the neck diameter itself. Wider necks were less oversized. For each additional millimeter in diameter, the oversizing decreased on average 3.3% (linear regression, p < 0.0001; correlation coefficient = -0.83). The diameter difference between device and proximal neck (expressed as percentage of neck
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diameter) was not associated with the probability of proximal type I endoleak. Overlapping of the device on the proximal neck was almost perfectly correlated with the neck length: for each additional millimeter in neck length, the overlapped distance increased 0.97 mm on average (linar regression, p < 0.0001; correlation coefficient = 0.99). Increasing neck length (p = 0.01) and overlapped length (p = 0.007) were associated with lower risks of proximal type I endoleak. For each additional 5 mm of overlapping, the chance of developing this type of endoleak decreased 0.5 times. The strengths and significance of associations between all the above characteristics and the occurrence of a proximal type I endoleak are summarized in Table II. After adjusting for each variable in a multivariate Cox proportional hazards model, all of the univariately significant associations remained significant. The model, whose overall significance reached a p value equal to 0.0001, is summarized in Table III.
DISCUSSION Data on the incidence of type I proximal endoleak are not especially abundant. Most reports tend to mention overall rates of type I endoleaks arising from both proximal and distal attachment sites or of both type I and III endoleaks. This tendency probably results from the conviction that these types of endoleak imply similar negative prognostic consequences. Nevertheless, proximal type I endoleaks have been reported with frequencies ranging from 016 to 2.6%.17 Both these studies, however, did not report estimated probabilities based on the number of patients at risk and respective follow-up time, making comparisons difficult with the present study’s estimated incidence (4% by 3 years in this study), which was calculated using the KaplanMeier method. The risk factors involved in the development of a proximal type I endoleak are certainly specific for this location, and there is some evidence that their clinical consequences might also differ from distal type I endoleaks. In fact, proximal type I endoleaks have been described as independent risk factors for post-EVAR rupture,13 whereas the same association was not demonstrated for endoleaks arising from distal attachment sites. For these reasons we were motivated to focus on isolated proximal type I endoleaks. Our study confirms that these are relatively rare events. Interestingly, three of the patients who had a postoperative proximal type I endoleak had already experienced the same complication intraopera-
Proximal type I endoleak after EVAR 625
tively. Presumably, the same hostile characteristics that did not allow achievement of an effective proximal seal continued to exert their deleterious action postoperatively, causing recurrence of the problem. As described elsewhere, the intraoperative occurrence of a proximal type I endoleak, even if corrected (and thus not visible at the last completion angiogran study), is associated with an increased risk of this complication during postoperative follow-up (Sampio et al., submitted for publication). The number of events (n = 8) is obviously too small for any statistically sound inference about the clinical consequences of this type of endoleak. Nevertheless, it is worth noting that one of the patients (12.5%) progressed to aneurysm expansion and rupture. This isolated instance in concurrence with most reports on the special significance of this complication.2,8,13 Attempts to classify the aneurysm proximal neck in terms of its shape have been dismissed in the currently recommended reporting standards as oversimplistic and of reduced applicability.15 We tried to use objective criteria in defining a reverse tapered neck. Intuitively, such necks would result in the ‘‘squeezing’’ of the device into the aneurysm sac. As in a previous study,18 our results did not provide any evidence to support this hypothesis. Angulated necks have been associated with poor outcome after EVAR.19 Specifically, type I endoleaks have been found more frequently in patients with proximal neck beta angles below 12019 or, conversely, patients with type I endoleaks have more acute proximal neck angles (17, mean).18 Petrik and Moore20 did not confirm this difference, but their study did not include patients with neck angles below 120, limiting the value of any comparisons. Despite finding a clear trend, our study failed to reach a significant association for this variable. Curiously, the only rupture occurred in a highly angulated neck. Thrombus in the aneurysm neck was one of the exclusion criteria for EVAR clinical trials. This exclusion was based on the assumption that neck thrombus posed an additional threat of three complications: proximal type I endoleak, device migration, and renal or distal embolization. As for type I endoleaks, the rationale for this association rests on two possible mechanisms of action: an immediate effect preventing a watertight seal, and deferred thrombus lysis, allowing for sac reperfusion and repressurization. These have been challenged by Gitlitz et al.,21 who found no early or late endoleaks (mean follow-up = 23 months; n = 19) in patients with more than three-fourths of the
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Table II. Impact of preoperative characteristics on proximal type I endoleak cumulative incidence rate by univariate Cox proportional hazards models analysis
Preoperative characteristic
Reverse tapered neck Angulated neck (>60) Percent of calcified neck wall Percent of thrombus-lined neck wall Neck thrombus thickness Percent of thrombosed neck cross-sectional area Neck length Device and neck overlap Device and neck oversize Aneurysm diameter Percent of thrombosed sac cross-sectional area
Hazards ratio of developing proximal type I endoleak
Increment
1.25 2.01 2.19 0.99
Yes or no Yes or no 25% 25%
0.48-2.71 0.98-4.14 1.09-4.17 0.64-1.57
0.6 0.057 0.019 0.996
0.96 0.96
1 mm 10%
0.79-1.16 0.66-1.4
0.644 0.849
0.61 0.53 0.82 1.98 0.74
5 mm 5 mm 10% 1 cm 10%
0.368-0.9 0.34-0.86 0-1.59 1.22-3.25 0.53-1
0.01 0.007 0.555 0.006 0.053
Hazards ratio 95% CI
p
CI, confidence interval.
Table III. Impact of preoperative characteristics on proximal type I endoleak cumulative incidence rate by multivariate Cox proportional hazards models analysis Preoperative characteristic
Hazards ratio of developing a proximal type I endoleak
Increment
Hazards ratio 95% CI
p
Overall model Percent of calcified neck wall Device and neck overlap Aneurysm maximal diameter
— 2.4 0.45 1.9
— 25% 5 mm 1 cm
— 1.19-4.9 0.26-0.81 1.07-3.39
0.001 0.01 0.008 0.03
CI, confidence interval.
neck wall lined with thrombus. One could argue that this way of classifying neck thrombus is too crude to detect any true effect, especially when it results in an ‘‘exposed’’ cohort of only 19 patients. In the present study, neck thrombus was evaluated using three different measurements, all of them in continuous instead of categorical scales. No impact of thrombus could be demonstrated, but some caution should be used in interpreting these results, because CT images read as thrombus might truly correspond to thick, noncalcified atheroma. Such cases might have been systematically wrongly classified on all studies (as thrombus-lined necks), diluting any potential effect of true neck thrombus. Nevertheless, aortic neck filling defects detected on CT scans do not seem to pose an additional risk of developing proximal type I endoleaks. One should also note that while a seal may be achieved when the endograft is implanted into thrombus proximally, this situation may lead to endotension, graft migration, and rupture, as noted by White et al.22
The potential relevance of endograft oversizing in the development of a proximal type I endoleak is related to endograft migration: excessively oversized grafts would be at a higher risk of being ‘‘squeezed’’ out of the aortic neck, especially devices without hooks or barbs. No reports exists on the direct impact of oversize on endoleak occurrence. Several studies23-26 have documented an association between neck dilation and graft oversizing, but conflicting reports also exist.27 Neck dilation, in turn, was associated with increased risk of device migration.23,25 Interestingly, no direct association was ever demonstrated between oversizing and device migration. Whether this simply reflects a lack of follow-up time to detect enough migration events remains to be elucidated. Device migration was clearly an implicated mechanism in at least half of the endoleak cases in our series, but no significant impact of oversizing could be documented. Calcification of the proximal neck could be implicated in sealing failure, through two potential
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mechanisms. Heavily calcified necks might be less flexible and more irregular, hence less able to fit closely around the endograft and achieve a hemostatic seal. Large surfaces of calcified plaque might constitute a more ‘‘slippery’’ wall, upon which the endograft could easily migrate. Calcification has only been proven under experimental conditions on cadaveric aortas to constitute a risk factor for endograft migration.28 Our results indicate that calcification may be associated with the probability of proximal type I endoleaks. Short necks have been proven to affect the incidence of intraoperative complications.29 The association between neck length and achievement of an effective proximal seal is intuitive. Either by providing a larger area of contact to obtain a hemostatic seal or by increasing the friction forces, making endograft displacement less likely, a long neck is generally seen as an advantageous feature. This is true to the extent that a longer neck actually means a longer distance of overlap, as was the case in our study. Neck length and neck and device overlap were closely correlated. This is an expected consequence of the adopted technique of placing the endograft immediately below the lowest renal artery, taking advantage of the total available proximal landing zone. These considerations might seem logical, but confirming clinical data are absent. Cao et al.23 did not find any significance for neck length in the genesis of device migration, but they evaluated this variable in a categorical fashion, classifying patients as having or not having necks shorter than 10 mm. Conners et al.25 also failed to show any effect of the degree of overlap, but they evaluated its impact in a non-time-dependent fashion, by comparing means between migrators and nonmigrators, not accounting for different lengths of follow-up or censoring. Greenberg et al.30 specifically tested the impact of short necks on endoleak rates, without any significant association. However, their total sample size was only 55, they defined their outcome of interest as any type of endoleak, and they performed their tests without taking follow-up duration or censoring into account. Our study found a highly significant impact of the length of the overlapped zone and the risk of a proximal type I endoleak. Of all the tested variables, this one achieved the highest level of significance and was one of the strongest factors. Our results are in concurrence with a previous work that identified this variable as a key feature in endograft migration in an experimental setting.28 Larger aneurysms have been reported to be at increased risk of developing a type I endoleak.31,32
Proximal type I endoleak after EVAR 627
Debate has ensued about the true meaning of such observations, since they might simply result from the demonstrable inverse correlation between aneurysm diameter and neck length.29,31 This correlation existed in our study, albeit weak and barely significant (correlation coefficient, –0.14; p = 0.046). Moreover, when included together in a multivariate Cox proportional hazards model, both variables remained independent predictors of proximal type I endoleak. The rationale for the deleterious effect of large aneurysm diameter could reside in the lack of support around the main body of the device, which increase its positional stability and decrease the friction forces that presumably help keep the endograft in place. This hypothesis concurs with the trend that our study found for an increased risk of proximal type I endoleaks in patients with less thrombus in their aneurysms: more empty space inside the sac increases the risk of a proximal seal failure. We believe the main weakness of this study lies in the low number of events detected. However, if this increased the risk of a type II error (as might have been the case in evaluation of the impact of neck angulation), it reinforces the significance of the demonstrable associations. Therefore, although we believe special caution should be used in interpretation of this study’s negative results, we are convinced that length of proximal fixation, neck calcification, and aneurysm size are meaningful independent risk factors for development a seal failure at the proximal attachment site.
CONCLUSIONS Proximal type I endoleak is a rare complication after EVAR, but it is associated with a high number of reinterventions and potentially serious consequences. Patients with large aneurysms and shorter and more calcified aneurysmal necks are at increased risk of such events. REFERENCES 1. Parodi JC, Palmaz JC, Barone HD. Transfemoral intraluminal graft implantation for abdominal aortic aneurysm. Ann. Vasc. Surg. 1991;5:491-499. 2. Zarins CK, White RA, Hodgson KJ, Schwarten D, Fogarty TJ. Endoleak as a predictor of outcome after endovascular aneurysm repair: AneuRx multicenter clinical trial. J. Vasc. Surg. 2000;32:90-107. 3. Harris PL. The highs and lows of endovascular aneurysm repair: the first two years of the EUROSTAR registry. Ann. R. Coll. Surg. Engl. 1999;81:161-165. 4. Shurink GWH, Arts NJM, Vanbockel JH. Endoleak after stent-graft treatment of abdominal aortic aneurysm. Br. J. Surg. 1999;86:581-587.
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