Duplex ultrasound factors predicting persistent type II endoleak and increasing AAA sac diameter after EVAR

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1 From the Society for Clinical Vascular Surgery Duplex ultrasound factors predicting persistent type II endoleak and increasing AAA sac diameter after EVAR Brian R. Beeman, MD, Kathy Murtha, RVT, Kevin Doerr, RVT, Sandy McAfee-Bennett, RVT, Matthew J. Dougherty, MD, and Keith D. Calligaro, MD, Philadelphia, Pa Objective: While the significance of type II endoleaks (T2ELs) on the long-term outcome of endovascular abdominal aneurysm repair (EVAR) to repair abdominal aortic aneurysms (AAAs) is debatable, duplex ultrasonography (DU) parameters have been suggested to be predictive of their closure or persistence. The purpose of this study was to determine which, if any, of these variables was associated with persistent T2EL or increased AAA sac diameter. Methods: Between 1998 and 2009, 278 patients underwent EVAR and post-operative DU surveillance during long-term follow-up (1-11 years) in our accredited non-invasive vascular laboratory by one of three experienced technologists. DU measured intra-sac flow velocity (IFV), spectral doppler waveform (SDW) patterns, post-evar sac diameter, and number of T2ELs. Results: T2ELs developed in 14% (38/278) of patients post-evar. Fourteen patients had T2ELs that resolved, and sac diameter decreased or remained the same: the average IFV was 42 cm/second; SDW patterns were monophasic in five, biphasic in seven and bidirectional in two; and multiple T2ELs were not present (0%) in any patient. Twelve patients had T2ELs that persisted, but sac diameter decreased or remained the same: the average IFV was 47 cm/second; SDW patterns were monophasic in one, biphasic in five, bidirectional in five, and undetermined in one; and multiple T2ELs were found in 17% (2) of patients. Twelve patients had T2ELs that persisted and were associated with increased sac diameter: the average IFV was 43 cm/second, SDW patterns were monophasic in one, biphasic in two, and bidirectional in nine; and multiple T2ELs were identified in 75% (9) of patients. None of the 38 patients with T2ELs treated with selective surgical or endovascular intervention for enlarging sac diameters (11/12) experienced a ruptured aneurysm. Conclusion: Contrary to previous smaller reports of T2ELs and DU surveillance, parameters such as IFV did not correlate with increased post-evar sac diameter. The presence of multiple T2ELs and bidirectional SDW may be the strongest factors predictive of increased sac diameter. (J Vasc Surg 2010;52: ) Since its initial description by Parodi et al in 1991, endovascular aortic aneurysm repair (EVAR) has offered a minimally invasive alternative to open abdominal aortic aneurysm (AAA) repair. 1 Successful treatment with EVAR requires the exclusion of arterial flow into the aneurysm sac, preventing continued expansion of aneurysm size and possible rupture. However, perigraft flow may persist or develop in the form of endoleak. Type II endoleaks (T2ELs) are the most common type and are due to patent branch vessels within the aneurysm sac such as the inferior mesenteric artery (IMA), lumbar arteries, or retrograde iliac artery collaterals. 2 Although many T2ELs will spontaneously close, some have been associated with sac expansion and rupture A few studies have examined the utility of duplex ultrasonography (DU) in determining which parameters may predict From the Section of Vascular Surgery, Pennsylvania Hospital. Competition of interest: none. Presented at the Thirty-eighth Annual Symposium of the Society for Clinical Vascular Surgery, Scottsdale, Ariz, Apr 7-10, Reprint requests: Keith D. Calligaro, MD, 700 Spruce St., Ste. 101, Philadelphia, PA ( kcalligaro@aol.com). The editors and reviewers of this article have no relevant financial relationships to disclose per the JVS policy that requires reviewers to decline review of any manuscript for which they may have a competition of interest /$36.00 Copyright 2010 by the Society for Vascular Surgery. doi: /j.jvs closure of these T2ELs. Intrasac flow velocity (IFV) more than 80 cm/second and certain spectral Doppler waveform (SDW) patterns, namely biphasic flow, have been suggested to correlate with endoleak persistence We previously demonstrated that DU in our noninvasive vascular laboratory by experienced registered vascular technologists (RVTs) can be safely used as a stand-alone study to follow EVAR patients in a cost-effective manner and avoid the risk of contrast agents and radiation. 18 The purpose of this study was to determine in a large patient cohort, which, if any, of these DU variables was associated with persistent T2EL or increased AAA sac diameter. METHODS From September 1998 until June 2009, 278 patients underwent EVAR by the Vascular Surgery Service at Pennsylvania Hospital in Philadelphia. Five types of endografts were used during this time period: Ancure (Endovascular Technologies, Menlo Park, Calif) early in our experience, and later AneuRx (Medtronic, Minneapolis, Minn), Excluder (W.L. Gore and Associates Inc, Flagstaff, Ariz), Zenith (Cook Medical Inc, Bloomington, Ind), and Powerlink (Endologix, Irvine, Calif). Our EVAR surveillance practice has changed considerably since the start of our endograft program. Before July 2004, our protocol consisted of computed tomography (CT) and DU scanning within 2 weeks of discharge, at

2 1148 Beeman et al JOURNAL OF VASCULAR SURGERY November 2010 and 12 months, and then yearly if no problems were found. DU and CT scans were equivalent in determining aneurysm sac diameter after EVAR (P.001). 18 Additional CTAs were ordered if AAA sac sizes increased by 0.5 cm within 6 months of prior evaluations. After this date, we obtained one CT and DU scan within 2 weeks of surgery and then performed DU at 6 and 12 months and then yearly without confirmatory CT scans if no problems were detected. We have previously shown a high specificity and sensitivity of DU in our vascular laboratory in detecting endoleaks and sac enlargement of AAAs following EVAR. 18 CT rarely recorded T2ELs correctly. 18 In fact, DU was our sole mode of surveillance after 2004 unless the AAA sac increased by 0.5 cm in size. In those circumstances, there was little correlation between CT and DU since DU was the study to document these T2ELs on multiple successive visits by the same vascular technician. All patients in the current series had follow-up DU scans performed in our accredited vascular laboratory by one of three experienced vascular technologists (K.M., K.D., S.M.-B.). Each patient was included in a prospectively maintained computerized registry (Access; Microsoft Corp, Redmond, Wash). High definition, color-flow Doppler equipment was employed using 2-4 MHz transducers with 10.4 software (Phillips HD-11, Phillips HDI- 5000, Phillips HD-3000, Bothell, Wash). After overnight fasting, examination with DU commenced with the patient in the supine position. Imaging of the aorta was performed from the celiac artery to the iliac bifurcation in the longitudinal and transverse axis. The iliac and common femoral arteries were scanned in a similar fashion. Transverse measurements relative to the vessel were made just proximal to the celiac artery, at the level of the renal arteries, at the maximal aneurysm diameter, and just proximal to the aortic bifurcation. Presence or absence of T2ELs by DU imaging was defined by real-time B-mode image data with SDW criteria with flow direction and IFV. Color-flow mode was used to help identify endoleaks and further focus on determination of origin. The source of peri-graft flow was categorized: lumbar, IMA, internal or external iliac artery collateral, or indeterminate. We also documented the presence of multiple branch endoleaks. Each T2EL was confirmed by the same technician at each follow-up visit. In addition, the majority of the T2ELs were found after 2004, and this is when we were using DU as our sole surveillance modality. 18 SDW criteria were characterized as three types (Fig 1): biphasic (high resistance with a reverse flow component in early diastole), monophasic (blunted with rounded peaks and no reverse flow in diastole), or bidirectional (to-fro) flow (similar to that described in the neck of a pseudoaneurysm with forward flow in systole and reverse flow in diastole). Each T2EL was documented with a velocity, location relative to the AAA sac, and SDW by the same technician at each follow-up appointment. Each velocity measurement was recorded from immediately within the AAA sac and immediately outside the sac. The highest value was recorded as the highest velocity. Fig 1. Spectral doppler waveforms. A, Biphasic. B, Monophasic. C, Bidirectional. This was a retrospective review of our prospectively maintained vascular registry to identify those EVAR patients with T2ELs. Multiple endoleaks mean more than one T2EL. For example, if a patient had two independent endoleaks, then we would describe two T2ELs for that particular patient. Only those patients who had T2ELs documented by either repeated DU studies or confirmatory CT scan or contrast arteriography were included in this

3 JOURNAL OF VASCULAR SURGERY Volume 52, Number 5 Beeman et al 1149 Table I. Doppler ultrasonography results of post-endovascular abdominal aneurysm repair Group 1 Group 2 Group 3 Number of patients Intrasac flow velocity (cm/sec) (mean) Spectral Doppler waveform Monophasic Biphasic Bidirectional Unknown Type 2 endoleak Number with 1 type 2 endoleak Number with multiple type 2 endoleaks Follow-up, months (mean) Abdominal aortic aneurysm sac diameter Decreased No change Increased Group 1, resolution of type 2 endoleak, no sac enlargement; Group 2, persistent type 2 endoleak, no sac enlargement; Group 3, persistent type 2 endoleak, sac enlargement. analysis. Three different groups of T2EL patients were identified: Group 1 (14 patients whose T2ELs resolved spontaneously and whose AAA sac decreased in size), Group 2 (12 patients who had persistent T2ELs and decreasing or stable AAA sac sizes), and Group 3 (12 patients who had persistent T2ELs that were both persistent and associated with an increasing AAA sac size; Table I). Statistical analysis was performed by the University of Pennsylvania s Biostatistics Analysis Center (BAC). The Fisher s exact test was used to compare the three groups with the following DU characteristics: IFV, SDW patterns, location of endoleak, and number of T2ELs. The alpha or significance level was set at Institutional Review Board approval was not obtained to perform this study, since we believed there had been reasonable justification to follow these patients in this manner based on our previous publication. 18 In addition, we felt the increased radiation risk of CT scans negated the potential adverse effects of deleting CT scans. RESULTS Of the 278 EVAR patients, 38 (14%) had T2ELs identified by DU (Table I). Patients were categorized into three groups. Group 1 included 14 patients with T2ELs that resolved spontaneously (range, 2-48 months) with AAA sac diameter decreased (71% [10/14]) or unchanged (29% [4/14]) during follow-up (mean, 38 months; range, months). Mean IFV was 42 cm/second (range, 9-82 cm/second). SDW patterns were monophasic in five patients, biphasic in seven, and bidirectional in two. Out of a total of 11 patients who had multiple T2ELs, only one had both IMA and lumbar endoleaks. All the rest had multiple lumbar T2ELs. All 14 patients in Group 1 had only one T2EL (ie, none (0%) had multiple endoleaks). T2ELs were due to lumbar arteries in nine patients and in unnamed branches in five. No patients in Group 1 underwent any interventions for endoleaks post-evar. Group 2 included 12 patients with persistent T2ELs whose AAA sac diameter decreased (25% [3/12]) or remained unchanged (75% [9/12]) during follow-up (mean, 31 months; range, months). Mean IFV was 47 cm/second (range, cm/second). SDW patterns were monophasic in one patient, biphasic in five, bidirectional in five, and undetermined in one. Multiple T2ELs (two per patient) were present in 17% (2/12) of patients. T2ELs were due to lumbar arteries in nine patients, IMAs in two, and unnamed branches in one. No patients underwent any interventions for endoleaks post-evar in Group 2. Of the Group 2 patients with multiple T2ELs, there were two patients with more than one or two T2ELs. Group 3 included 12 patients with persistent T2ELs with increased sac diameter during follow up (mean, 65 months; range, months). Mean IFV was 43 cm/ second (range, cm/second). SDW patterns were monophasic in one patient, biphasic in two, and bidirectional in nine. Multiple T2ELs (two in six patients, three in three patients) were present in 75% (9/12) of patients (Fig 2). T2ELs were due to lumbar arteries in 10 patients and IMAs in two patients. Eleven of 12 Group 3 patients underwent a secondary intervention to treat an increasing AAA sac diameter: transcatheter embolizations with transarterial and translumbar coils, thrombin, or glue in 10 patients and laparotomy with oversewing of a lumbar T2EL in one patient. One patient was deemed too high risk for further intervention. Treatment for 5 of 11 patients resulted in resolution of the T2EL with sac contraction, while six patients demonstrated continued sac enlargement. Two patients were deemed too high risk for surgery and were followed with DU every 3 months. Two patients declined open surgical repair when given this option. One patient underwent an additional endovascular attempt at coil embolization. One patient expired from unrelated causes. Group 3 (12 patients), of which there were nine patients with more than one type 2 endoleak. In these cases, six patients had two T2ELs and three patients had three type 2 endoleaks. Of the patients in Groups 2 and 3 with persistent T2ELs, 71% (17/24) had IFV 80 cm/second. For Group 3 patients who required intervention for increasing AAA sac diameter, 67% (8/12) had IFV 80 cm/second. IFV (P.1805) and location of T2ELs (P.0868) did not predict sac growth in our cohort (Table II). However, the presence of a bidirectional Doppler flow pattern (P.0069) and the presence of multiple T2ELs (P.0001) were found to be predictive for sac expansion post-evar (Table II). None of the 38 patients with T2ELs followed by DU for EVAR surveillance experienced a ruptured aneurysm. When considering all 3 groups and SDWs, the average IFV values of monophasic waveforms were 41 cm/second (range, cm/second). The average IFV values of

4 1150 Beeman et al JOURNAL OF VASCULAR SURGERY November 2010 a faster rate of expansion. Mean follow-up for each group was Group 1 (38 months), Group 2 (31 months), and Group 3 (65 months). Fig 2. Patients from group 3 with type II endoleaks. bidirectional waveforms were 50 cm/second (range, cm/second). The average IFV values of biphasic waveforms were 43 cm/second (range, cm/second). IFV could neither differentiate SDW patterns nor determine future AAA sac size enlargement or persistence of T2EL, as other studies have suggested. The overall rate of AAA sac expansion following EVAR was 0.5 cm per year on average with a range of 0.2 to 2 cm per year. Those patients with multiple T2ELs did not have DISCUSSION T2ELs are the most common endoleak following EVAR. 3 The long-term significance of T2ELs is unknown. Systemic pressure can be recorded in the aneurysm sac of patients with T2ELs and is a cause for concern for rupture risk. 19 Several studies have shown that patients without endoleak have a decrease in AAA sac size over time, while those with a persistent endoleak may experience sac growth and rupture. 2,4,5,10,12 DU is being increasingly utilized for surveillance following EVAR Characteristics that can predict which patients will experience sac growth or endoleak persistence following EVAR have been investigated While most groups, including our own, do not intervene on T2ELs unless sac diameter increases, others advocate a more aggressive approach and treat all T2ELs that persist beyond 6 months. 4,8,10,11,17,20,21 Other studies have attempted to use DU characteristics to predict the behavior of T2ELs and AAA sac size following EVAR Arko et al reported that T2EL intrasac flow velocities (IFV) 80 cm/second were likely to resolve without treatment and that those with velocities 100 cm/second were related to large branch vessel diameter and multiple endoleaks. 16 They also suggested that higher velocity endoleaks were more resistant to transarterial embolization. 16 A critical finding of our study is that IFV did not correlate with likelihood of closure of T2EL, nor did high IFV predict sac enlargement. In addition, the velocity and multiplicity of T2ELs was not additive for AAA sac expansion. In other words, those with multiple branch endoleaks did not have higher velocities and, therefore, a greater chance at sac expansion post-evar. Meier et al suggested that SDW patterns can differentiate endoleaks that spontaneously seal from those that persist They suggested that bidirectional to-fro waveforms in T2ELs may precede occlusion, while waveforms that remain biphasic with characteristics similar to normal peripheral arterial flow appear to predict persistent endoleak. 13 Our findings contradict their results (Table II). In our study, 9 of 16 (56%) patients with bidirectional SDWs had increased AAA sac diameter during follow up. Conversely, patients with biphasic waveforms (8/14 [57%]) were the most likely to have a decreased AAA sac diameter over time (Table II). Bidirectional to-fro waveforms could be predictive of AAA sac enlargement due to the following mechanism: An endoleak can connect a higher pressure inflow source (lumbar or IMA) with an outflow vessel such as another nearby lower pressure lumbar vessel we would see biphasic SDWs much as normal peripheral arteries. However, if the lumbar or IMA has only an inflow source into the AAA sac and no nearby lumbar or other feeding vessel, the SDW would reveal the to-and-fro SDW. The to-and-fro SDW reflects the lack of an outflow source vessel and thus increases the

5 JOURNAL OF VASCULAR SURGERY Volume 52, Number 5 Beeman et al 1151 Table II. Statistical analysis of type 2 endoleaks and aortic sac size Predictor Value Decreased sac size Stable sac size Increased sac size P value Location Lumbar artery 8 (29.6%) 9 (33.3%) 10 (37.0%).0868 Inferior mesenteric artery 0 (0.0%) 1 (33.3%) 2 (66.7%) Unknown 5 (71.4%) 2 (28.6%) 0 (0.0%) Lumbar inferior mesenteric artery 0 (0.0%) 1 (100.0%) 0 (0.0%) Spectral Doppler waveform Biphasic 8 (57.1%) 4 (28.6%) 2 (14.3%).0069 Bidirectional 1 (6.3%) 6 (37.5%) 9 (56.3%) Monophasic 3 (50.0%) 3 (50.0%) 0 (0.0%) Unknown 1 (50.0%) 0 (0.0%) 1 (50.0%) Velocity (cm/sec) (40.6%) 10 (31.3%) 9 (28.1%) (0.0%) 3 (50.0%) 3 (50.0%) Number of type II endoleaks One 13 (48.1%) 11 (40.7%) 3 (11.1%).0001 Multiple 0 (0.0%) 2 (18.2%) 9 (81.8%) diastolic pressure in the AAA sac; the net effect is to increase the mean pressure in the AAA sac. Our study is to date the largest published focusing on DU parameters and T2EL resolution. The only statistically significant predictors for sac growth were multiple T2ELs and bidirectional Doppler flow. We found that endovascular intervention for expanding AAA sac diameter due to T2ELs was successful in preventing future sac growth in only slightly more than half of the cases. These disappointing results with embolization were mirrored by Sheehan et al, who reported a 20% rate of increased AAA sac size following transcatheter coiling of T2ELs. 11 Success of DU alone for EVAR surveillance depends greatly on RVT experience and accuracy. An adequate exam can be very time-consuming. Most vascular surgeons believe that increasing AAA sac size following EVAR is the most important DU parameter to document at each follow-up visit, since this factor is the one that most likely predicts sac rupture. 2 Our data suggest that the number of T2ELs is the strongest predictor of sac growth. The next logical step concerning post-evar surveillance is to determine whether sac enlargement alone is the best predictor or sac rupture, and if all other parameters are insignificant. Our current practice is to observe T2ELs as long as the aneurysm sac is stable or shrinking. However, if the AAA sac diameter increases by 5 mm, the endoleak is treated. Knowledge of the presence of multiple T2ELs or bidirectional Doppler flow would lead us to perform more frequent EVAR surveillance and possibly earlier intervention. We thank Amy Praestgaard, MS, (Director, Biostatistics Analysis Center, Center for Clinical Epidemiology and Biostatistics, University of Pennsylvania School of Medicine) for her help with the statistical interpretation of our data. AUTHOR CONTRIBUTIONS Conception and design: BB Analysis and interpretation: BB Data collection: BB, KM, KD, SB Writing the article: BB, KC Critical revision of the article: MD, KC Final approval of the article: MD, KC Statistical analysis: BB Obtained funding: BB Overall responsibility: BB REFERENCES 1. Parodi JC, Palmaz JC, Barone HD. Transfemoral intraluminal graft implantation for abdominal aortic aneurysms. Ann Vasc Surg 1991;5: Heikkinen MA, Arko FR, Zarins CK. What is the significance of endoleaks and endotension? Surg Clin N Am 2004;84: Jones JE, Atkins MD, Brewster DC, Chung TK, Kwolek CJ, LaMuraglia GM, et al. Persistent type 2 endoleak after endovascular repair of abdominal aoric aneurysm is associated with adverse late outcomes. J Vasc Surg 2007;46: Baum RA, Carpenter JP, Golden MA, Velazquez OC, Clark TWI, Stavropoulous W, et al. Treatment of type 2 endoleaks after endovascular repair of abdominal aortic aneurysms: comparison of transarterial and translumbar techniques. 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