Common Femoral to Iliac Artery Ratio Predicts Type IB Endoleak in Patients Undergoing Endovascular Aneurysm Repair (EVAR)
Sally Boyd1, Kedar Lavingia2, Luke Wolfe1, Michael Amendola2
1Virginia Commonwealth University Health System, Richmond, VA;2Central Virginia VA Health Care System, Richmond, VA
INTRODUCTION:Type 1B Endoleak (T1B-E) after endovascular aortic aneurysm repair (EVAR) represents a failure of the distal portion of the endograft to adequately seal to the vessel wall, potentially perpetuating aneurysmal dilation. The incidence of T1B-E is estimated to be approximately 4.4% for elective cases1. With regards to T1B-E, a paucity of data is centered around T1B-E, however larger diameter or aneurysmal iliac vessels have shown to have higher propensity for future interventions and subsequent development of T1B-E2-6. The aim of our analysis was to evaluate the bilateral common iliac artery (CIA) and common femoral artery (CFA) diameters in patients who underwent EVAR in our facility and the subsequent development of Type 1B Endoleak. We use CIA:CFA diameter ratio to better assess the relative dilation of the CIA compared to the CFA.
METHODS:After obtaining IRB approval, we retrospectively reviewed our Veterans Administration Hospital EVAR database from January 2011 to January 2015 to identify all patients who underwent EVAR. Preoperative computerized topography (CT) scans were examined. Proximal common iliac artery measurements were taken at the first axial cut beyond the aortic bifurcation. Bilateral common femoral artery measurements were taken at the first axial cut proximal to the origin of the profunda femoris artery. The vessels were measured using standard ruler tool on our imaging platform. The CIA:CFA ratio was calculated for each patient using combined measurements from both left and right CIA and CFAs. Need for secondary intervention for T1B-E was followed for 6 years postoperatively. Patient comorbidities, demographics, fluoroscopy time, and mortality rates were collected. Fishers Exact Test* and unpaired t-test** were utilized to compare the differences between patients who developed T1B-E to those that did not develop T1B-E. Receiver operator characteristic curve and Cox Regression were also utilized to assess the ability of CIA:CFA ratio to predict need for later intervention.
RESULTS:Eighty-five patients underwent EVAR during this time period examined with 8.2% (n=7) developing a Type 1B Endoleak (T1B-E) with mean time to repair of 2014 ± 1214 days. One patient had both Type 1A and Type 1B endoleaks. For those requiring repair, two were bilateral, three isolated to the left side, and two on the right. Patients who developed Type 1B Endoleaks (T1B-E) were compared to those that did not develop Type 1B Endoleaks (no T1B-E). There was no significant differences between the two groups in terms of comorbidities, demographics, and mortality rates with the exception of white race (85.7% in the no T1B-E group v. 42.8% in the T1B-E group, p=0.01*), chronic kidney disease (CKD) (15.6% in the no T1B-E group v. 57.1% in the T1B-E group, p=0.02*), and peripheral vascular disease (PVD) (9.0% in the no T1B-E group v. 42.8% in the T1B-E group, p=0.03*) (Table 1). The average combined proximal common iliac artery was 37.2 ± 13.4 in the no endoleak group and 48.8 ± 19 in the T1B-E group (p=0.04**) (Table 2). The average combined common femoral artery diameter was 25.4 ± 5.6 in the no T1B-E group and 25.2 ± 6.5 in the T1B-E group (p=0.09**) (Table 2). The average CIA:CFA ratio in the no T1B-E group was 1.47 ± 0.47 and in the T1B-E group was 1.99 ± 0.76 (p=0.01**) (Table 2). Receiver operating characteristic curve shown in Figure 1 demonstrates the predictive nature of CIA:CFA ratio when CKD, PVD, and race are entered in a stepwise fashion (area under the curve = 0.883). Using CIA:CFA ratio, race, CKD, PVD as covariates, Cox regression demonstrated that CIA:CFA ratio, CKD, and PVD increase the risk of requiring a secondary intervention. The hazard ratio (HR) for the CIA:CFA variable is 5.89 (95% CI 1.39-24.9, p=0.016). The HR for CKD was 10.03 (95% CI 1.73-58.0, p=0.01) and for PVD was 12.04 (95% CI 1.87-77.7, p=0.009). Race did not significantly increase the risk for reintervention (Figure 2).
CONCLUSIONS:In our retrospective, single-center examination of a veteran population undergoing EVAR with a six-year follow-up, we found that CIA:CFA Ratio is predictive of subsequent need for reintervention for Type 1B Endoleak (T1B-E).Studies have described the need for secondary intervention in patients with challenging iliac anatomy including smaller external iliac arteries7, hostile iliac artery anatomy (defined as >90-degree iliac angulation, >50% circumferential calcification, hemodynamically significant stenosis or obstruction of iliac arteries, small external iliac (<7mm), or previous aortoiliac/femoral graft)7. For T1B-E specifically, diameter of iliac artery may play an important role in the need for later intervention. In one retrospective study, patients who underwent EVAR with iliac limbs >20mm (with the patient’s distal common iliac artery measuring >16mm) had an increased risk of developing late T1B-E in the 5 year follow up. The authors concluded that larger diameter iliac arteries may not be adequate for sealing at the distal landing zone and therefore pose a higher risk for development of endoleak 2. Another study also determined that dilated common iliac arteries (diameter >16mm) were more dilated at average follow up of 44 months than those with diameter < 16mm3. Richards et. al also found that common iliac arteries larger than 16 mm were more likely to expand during duplex surveillance for abdominal aortic aneurysm (AAA)4. In one study utilizing the EUROSTAR database, patients who had iliac artery aneurysmal disease were more likely to develop T1B-E than those who did not have iliac aneurysm5. The bell bottom technique (BBT) uses an enlarged, pathologic artery as the distal sealing zone. This technique is associated with a subsequent increase in CIA size due to the radial force of the graft at this distal landing zone. Therefore, use of BBT may increase the risk for type 1B endoleak6. These studies examine the absolute diameter of iliac vessels while our study uses the CIA:CFA diameter ratio to assess the relative dilation of the CIA as compared to the CFA. One weakness of our study is the small sample size, population limited to one facility, and a largely veteran population that has poor female representation. Our findings suggest that enhanced surveillance based on assessment of preoperative imaging may help diagnose and reintervene on T1B-E earlier. Additionally, vascular surgeons should potentially consider surgical options other than standard EVAR approach in patients with a higher CIA:CFA ratio.
|Preoperative Characteristic||No T1B-E (n=77)||T1B-E (n=7)||p-value|
|Age (years ± SD)||70.4 ± 7.56||69.9 ± 8.40||NS|
|White race (%)||85.7||42.9||p=0.01*|
|Coronary artery disease (%)||45.4||42.3||NS|
|Diabetes Mellitus (%)||31.2||14.3||NS|
|OR time (minutes ± SD)||146 ± 27.8||149 ± 19.3||NS|
Table 1: Preoperative characteristics of patients undergoing EVAR in both patients who subsequently developed type 1B endoleak and in those who did not develop type 1B endoleak. SD: standard deviation; COPD: chronic obstructive pulmonary disease; CKD: chronic kidney disease; PVD: peripheral vascular disease; CVA: cerebrovascular accident; PTSD: post-traumatic stress disorder; BMI: body mass index; OR: operating room;
|Measurement||Table of Contents||T1B-E(n=7)||p-value|
|Average Combined CIA (mm ± SD)||37.2 ± 13.4||48.8 ± 19||0.04|
|Average Combined CFA (mm ± SD)||25.4 ± 5.6||25.2 ± 6.5||0.09|
|Average CIA:CFA Ratio||1.47 ± 0.47||1.99 ± 0.76||0.01|
Table 2: Artery measurements at CIA and CFA and calculated CIA:CFA ratio in patients with no endoleak and in patients who experienced endoleak in the study period. CIA: common iliac artery; SD: standard deviation; CFA: common femoral artery
Figure 1: Receiving Operator Characteristics Curve for Combined Proximal Common Iliac Artery Diameter to Combined Common Femoral Artery Diameter Ratio using a stepwise selection method where CKD, PVD, and CIA:CFA ratio were considered significant factors. Race was removed from the model as it was not a significant factor. AUC: Area under curve; CI: Confidence Interval
Figure 2: Cox Regression with cumulative intervention free survival (reintervention for T1B-E) and time since initial operation in days using CIA:CFA ratio, CKD and PVD as covariates. CIA: common iliac artery; CFA: common femoral artery; CKD: chronic kidney disease; PVD: peripheral vascular disease
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