Compliance of postendovascular aortic aneurysm repair imaging surveillance

Abstract

Objective

Imaging surveillance after endovascular aortic aneurysm repair (EVAR) is critical. In this study we analyzed compliance with imaging surveillance after EVAR and its effect on clinical outcomes.

Methods

Retrospective analysis of prospectively collected data of 565 EVAR patients (August 2001-November 2013), who were followed using duplex ultrasound and/or computed tomography angiography. Patients were considered noncompliant (NC) if they did not have any follow-up imaging for 2 years and/or missed their first post-EVAR imaging over 6 months. A Kaplan-Meier analysis was used to compare compliance rates in EVAR patients with hostile neck (HN) vs favorable neck (FN) anatomy (according to instructions for use). A multivariate analysis was also done to correlate compliance and comorbidities.

Results

Forty-three percent were compliant (7% had no follow-up imaging) and 57% were NC. The mean follow-up for compliant patients was 25.4 months (0-119 months) vs 31.4 months for NC (0-140 months). The mean number of imaging was 3.5 for compliant vs 2.6 for NC (P< .0001). Sixty-four percent were NC for HN patients vs 50% for FN patients (P = .0007). The rates of compliance at 1, 2, 3, 4, and 5 years for all patients were 78%, 63%, 55%, 45%, and 32%; and 84%, 68%, 61%, 54%, and 40% for FN patients; and 73%, 57%, 48%, 37%, and 25% for HN patients (P = .009). The NC rate for patients with late endoleak and/or sac expansion was 58% vs 54% for patients with no endolcak (P = .51). The NC rate for patients with late reintervention was 70% vs 53% for patients with no reintervention (P = .1254). Univariate and multivariate analyses showed that patients with peripheral arterial disease had an odds ratio of 1.9 (P = .0331), patients with carotid disease had an odds ratio of 2 (P = .0305), and HN patients had an odds ratio of 1.8 (P = .0007) for NC. Age and residential locations were not factors in compliance.

Conclusions

Overall, compliance of imaging surveillance after EVAR was low, particularly in HN EVAR patients, and additional studies are needed to determine if strict post-EVAR surveillance is necessary, and its effect on long-term clinical outcome.

Endovascular aortic aneurysm repair (EVAR) has become the primary treatment for infrarenal abdominal aortic aneurysms (AMs). In the modern era, approximately 75% of AMs are repaired using EVAR in the United States.¹ Of patients who undergo EVAR, 13% to 22% require reintervention.^2,3 Several studies have compared different aspects of aortic neck morphology as a predictor of outcome after EVAR. Aortic neck angulation of >45°, a short infrarenal neck, a large aortic neck, and large aneurysms (>6.5 cm in diameter) are predictors of reintervention^4,5 and associated with increased rates of aneurysm-related morbidity.^6,7It is our opinion that patients who have had EVAR outside of the instructions for use (IFU; ie, with a hostile neck (HN) feature, defined by a neck angle of ≥60°), neck length <10 mm, ≥50% circumferential proximal neck thrombus, ≥50% circumferential calcified proximal neck, a diameter >31 mm, or reverse taper should have strict surveillance protocols.

The Society for Vascular Surgery (SVS) established lifelong surveillance guidelines for patients who undergo EVAR.⁸ These guidelines included computed tomography (CT) scanning at 1 and 12 months in tl1e first postoperative year and additional CT imaging at 6 months if an abnormal ity is detected at the first postoperative month scan. After 12 months, CT scanning is recommend ed annually, with the option of duplex ultrasound imaging if no abnormality is detected during the first year.^8,9 Even with the SVS-recommended surveillance guidelines and the logi cally modified alternative protocols, postoperative EVAR surveillance imaging compliance remains poor.^9,10 Patients who underwent EVAR at higher-volume centers were independently associated with complete su1veillance, and low-volume centers showed higher rates of noncompliance and l oss to follow-up.^9,11 Several studies have reported on post-EVAR imaging stuveillancc compliance.^9-13 Our present study will analyze post-EVAR imaging surveillance compliance and its effect on clinical outcome.

METHODS

This was a retrospective analysis of prospectively collected data of 565 patients who underwent EVAR using commercially available devices for infrarenal aortic aneu1ysms by solely the full-time faculty at our institution during a recent 12-year period (August 2001-November 2013). Patients with ruptured AAAs were not included in this analysis. All patients were followed originally according to the recommendations of the manufacturer (ie, postoperative imaging [CT angiography (CTA)] and/or duplex ultrasound) with a clinic visit at the Vascular Center of Excellence at 30 days after the procedure. These were repeated at 6 and 12 months, then yearly thereafter; however, over the past few years, our protocol was modified to include a CTA and/or duplex ultrasound scan at 30 days postoperatively, and, if normal, only a duplex ultrasound was obtained at 6 and 12 months, then followed annually. CTA was only done for patients who showed an endoleak on duplex ultrasound and/or enlarging aortic sac size. It should be noted that all patients were initially instructed by the operating physician and/or designated personnel (resident, fellow, physician assistant, or registered nurse) of the importance of post-EVAR imaging surveillance , which was also repeated during the post-EVAR discharge instructions and during the routine follow-up visits at the Vascular Center of Excellence. Every effort was made to contact these patients a few days before the next imaging/clinic visit by the charge nurses or clinic support staff. All postoperative inpatient or outpatient imaging, which were identified from the electronic medical records or the Vascular Center of Excellence visit notes, were reviewed for the presence of endoleak, aortic sac size changes, including regression, stability, enlargement, or graft migration. All post-EVAR duplex ultrasound scans were done at our accredited vascular laborato1y; similarly, all post-EVAR CTA scans were done at our medical center, except for occasional patients who might have their CT scan performed at an outside institution.

Patient demographic and clinical characteristics were recorded, including age, sex, geographic residential location according to city, county, state, and zip code. Indications for the procedure were classified as elective (asymptomatic) or symptomati c. All comorbidities were also recorded , including the presence of congestive heart failure, corona1y artery disease, peripheral arterial disease, chronic obstructive pulmonary disease, cerebrovascular disease, chronic renal insufficiency, diabetes mellitus, hyperlipidemia, and hypertension.

Aortic neck anatomic features were also reviewed from previous preoperative CTA imaging. Patients were classified accordingly into EVAR patients with HN features (outside IFU) vs favorable neck (FN) features (IFU p•ltients). HN features included : neck length of <10 mm, neck angle of <60°, ≥50% circumferential proximal neck thrombus (2:2 mm thick), ≥50% circumferential calcified proximal neck, reverse taper, and a diameter >31 mm. This study was approved by West Virginia University / Charleston Area Medical Center institutional review board with waiver of consent because the study was retrospective and the data did not contain patient names.

Definitions

Patient compliance of post-EVAR imaging surveillance was classified into compliant vs noncompliant (NC) groups. Patients were considered NC if they did not have any follow-up imaging (CT and/or duplex ultrasound) for 2 years at any time during their follow-up and/or missed their first post-EVAR imaging over 6 months.

Compliance was compared in patients with HN (outside IFU) vs patients with FN anatomic features (IFU patients). This was done on the basis of the presumption that patients with HN anatomy (or outside IFU) might be at higher risk of late adverse outcomes (eg, late endoleak, sac expansion, and/or intervention); therefore they might need more strict post-EVAR imaging surveillance. Compliance was also correlated with late clinical outcome, specifically patients who had late endoleak and/or late reintervention or sac enlargement to show the effect of loss of compliance on these outcomes.

Statistical analysis

A statistical analysis was performed using SAS version 9.2 software (SAS Institute Inc, Cary, NC). Categorical variables were compared using contingency table analysis with χ² or Fisher exact test. A Kaplan-Meier analysis was used to compare compliance rates in EVAR patients with HN vs FN anatomy (according to IFU). Statistical comparisons were made with the logrank test. A multivariate logistic regression analysis was also done to correlate compliance, comorbidities, and other factors.

RESULTS

Five hundred sixty-five EVAR patients were analyzed. These included: 304 Excluder (W. L. Gore and Associates, Flagstaff, Ariz), 108 Zenith (Cook Corp, Indianapolis, Ind), 75 AneuRx, 34 Talent, and nine Endurant (Medtronic Corp, Santa Rosa, Calif), 33 Powerlink (Endologix, Irvine, Calif), and two Trimodular (TriVascular, Inc, Santa Rosa, Calif). Thirty-nine of 565 patients with no or suboptimal preoperative CT imaging to define neck features were not included in the analysis of compliance according to neck fratures. In Table I we summarize the compliance rate in the whole se1ies. Only 43% of patients were fully compliant. The mean follow-up for compliant patients was 25 .4 months (range, 0-119 months) vs 31.4 months (range, 0-140 months) for NC patients. The mean number of imaging was 3.5 (range, 1-10) for compliant patients vs 2.6 (range, 0-10) for NC patients (P = .0001). The demographic and clinical characteristics are summarized in Table II. As noted, NC rates were significantly higher in patients with peripheral arterial disease and carotid arte1y disease. Age, whether <75 vs ≥75 or <80 vs ≥80, was not a significant factor for compliance. Similarly, there was no correlation with patient residential location and compliance, whether these patients lived in same county of the medical center or other counties (referring localities).

Table I.

Rates of compliance and noncompliance

Variable	Frequency	Percentage
Compliant	242	43
No follow-up imaging	42	7
Missed first post-EVAR up to 6-month  imaging	85	15
No follow-up imaging for 2 years	196	35
Total	565	100

EVAR, Endovascular aortic aneurysm repair.

Table II.

Demographic and clinical characteristics and compliance (N = 565)

Characteristic	Compliant (n = 242)	NC (n = 323)	P
Age, years
<75	139 (45)	172 (55)	.3221
≥75	103 (41)	151 (59)
<80	176 (44)	225 (56)	.4266
>80	66 (40)	98 (60)
Sex
Male	197 (43)	264(57)	.9205
Female	45 (43)	59 (57)
Hypertension
Yes	211 (43)	277(57)	.6236
No	31 (40)	46(60)
Hypcrlipidemia
Yes	165 (45)	203 (55)	.188
No	77 (39)	120(61)
Smoking (past and present)
Yes	142 (40)	214 (60)	.0649
No	100(48)	109(52)
Diabetes mcllitus
Yes	44 (37)	75 (63)	.1461
No	198 (44)	248 (56)
Coronary artery disease
Yes	132 (40)	198 (60)	.107
No	110 (47)	125 (53)
Congestive heart failure
Yes	32 (43)	42 (57)	.9388
No	210 (43)	281 (57)
Peripheral artery disease
Yes	19 (30)	44 (70)	.031
No	223 (44)	279 (56)
Chronic obstructive pulmonary disease
Yes	79 (43)	105(57)	.9726
No	163 (43)	218 (57)
Home oxygen
Yes	17 (50)	17(50)	.3836
No	225 (42)	306(58)
Chronic renal insufficiency
Yes	44 (38)	71 (62)	.267
No	198 (44)	252 (56)
Carotid disease
Yes	18 (29)	44(71)	.02
No	224 (45)	279 (55)
Race
White	239 (43)	313 (57)	.1453
Others	3 (23)	10(77)
Symptomatic AAA
Yes	38 (54)	33 (46)	.0533
No	204 (41)	289(59)
Geography (distance); Kanawha Countya
Yes	103(44)	129(56)	.5304
No	139 (42)	194 (58)
Geography (distance); CAMC primary service areab
Yes	160 (45)	195 (55)	1621
No	82 (39)	128 (61)

AAA, Abdominal aoitic aneurysm; CAMC, Charleston Area Medical Center; NC, noncompliant.

Data are presented as n (%).

^aKanawha County is the location of CAMC.

^bNeighboring counties that refer to CAMC.

Two hundred fifty-one patients (48%) had FN features and 275 patients (52%) had HN features. Sixty-four percent of patients with HN features were NC vs 50% for patients with FN features (P = .0007; Table III).

Table III.

Neck anatomy and compliance

	HN
Compliance	No	Yes	Total	P
Compliant	126	98	224	.0007
	50%	36%
NC	125	177	302
	50%	64%
Total	251	275	526

HN, Hostile neck; NC, noncompliant.

Compliance rates and late clinical outcome

The NC rate for patients with late endoleak and/or sac expansion was 58% vs 54% for patients with no endoleak and/or sac expansion (P = .51). The NC rate for patients with late reintervention was 70% vs 53% for patients with no late reintervention (P = .1254; Table IV). The overall mortality rate in compliant patients was 17.8% (43 of 242 [three of these were ruptured aneurysm-related]) vs 4.2% (12 of284 [none were aneurysm-related]) for NC patients (P< .0001). Other noted late complications included: two graft migrations (one in each group) and one late limb occlusion (in the NC group).

Table IV.

Compliance and late clinical outcomes

Compliance	No	Yes	Total	P
Late cndolcak and/or sac expansion
Compliant	219	23	242	.51
	47%	42%
NC	252	32	284
	54%	58%
Total	471	55	526
Late Rcintcrvention
Compliant	235	7	242	.1254
	47%	30%
Noncompliant	268	16	284
	53%	70%
Total	503	23	526

NC, Noncompliant.

Kaplan-Meier analysis and compliance

The rates of compliance at 1, 2, 3, 4, and 5 years for all patients were: 78%, 63%, 55%, 45%, and 32%. When compliance was correlated with aortic neck features, the compliance rates were: 84%, 68%, 61%, 54%, and 40% for patients with FN anatomy vs 73%, 57%, 48%, 37%, and 25% for patients with HN (P = .009; Fig).

Fig.

Graph showing compliance for patients with a favorable neck (FN), hostile neck (HN), and the whole series for 5 years.

Univariate and multivariate analysis of compliance and comorbidities

In Table V the univa1iate and multivariate analysis of compliance according to comorbidities is summarized. As noted in this table, using a univariate model, patients with a history of peripheral artery disease, carotid artery disease, and patients with HN features have significantly higher rates of noncompliance. However, age and residential location had no effect on compliance. In the multivariate model, only patients with carotid artery disease (odds ratio, 1.97; 95% confidence interval, 1.07-3.65; P = .0318) and HN features (odds ratio, 1.84; 95% confidence interval, 1.29-2.61; P = .0007) had significantly higher rates of noncompliance.

Table V.

Univariate and multivariate analyses of comorbidities and other factors and/or compliance

Comorbidity	Noncompliance	P
Univariate
Indication: symptomatic	0.61 (0.37-1.01)	.0549
Tobacco use (current or past)	1.38 (0.98-1.95)	.0653
PVD	1.85 (1.05-3.26)	.0331
Carotid disease	1.96 (1.10-3.49)	.0218
HN (outside IFU)	1.82 (1.28-2.58)	.0008
Age (>75 years)	1.17 (0.83-1.63)	.3725
CAMC service areaa	0,78 (0.55-1.11)	.1624
Multivariate
Indication: symptomatic	0.58 (0.34-0.97)	.0385
Carotid disease	1.94 (1.05-3.61)	.0349
HN (outside IFU)	1.85 (1.30-2.63)	.0007

HN, Hostile neck; IFU, instructions for use; PVD, peripheral vascular disease.

^aKanawha, Logan, Boone, Fayette, and Putnam counties.

DISCUSSION

Our study shows relatively poor compliance results for post-EVAR imaging surveillance in patients who undergoing EVAR. Of 565 patients, 57% were NC; patients with HN anatomy had a 64% noncompliance rate, and those with FN anatomy and characteristics had a 50% noncompliance rate. The noncompliance rate for patients with a finding of a late endoleak or sac expansion was 58%, compared with 54% for patients with no endoleak or sac expansion. Also, patients who required a late reintervention had noncompliance rates that approached 70% in contrast to 53% for patients who requiring no subsequent interventions. These were patients who had identified abnormalities during surveillance imaging or complications that required an additional procedure. Yet these two obviously concerning scenarios failed to encourage compliance with surveillance protocols designed to identify and treat a potentially life-threatening development. West Virginia is a rnral state, which requires significant travel by patients to tertia1y centers. However, distance was not a significant variable in noncompliance in our study. Our patients tend to be afflicted by multiple comorbidities, including renal insufficiency; yet this parameter, which arguably included the fear of nephrotoxicity, was not significant. Indeed, despite substitution of duplex ultrasound for CT imaging in our protocol, compliance remains low. Unfortunately, recent studies that have investigated this same issue have had similar findings, and attempts have failed to provide any consistent explanations for these results.

As EVAR becomes more widely applied to AAA repair in the elective and emergent settings, it has become imperative to establish protocols to provide effective surveillance evaluation and to allow subsequent interventions, if necessary. In the modern era of abdominal anernysm treatment, approximately 75% are repaired using EVAR in the United States.¹ Of those who undergo EVAR, 13% to 22% will require reintervention.^2,3 A short infrarenal neck, neck angulation of >45°, and large aortic neck (>28 mm) are predictors of reintervention,^4,5 and large aneurysms (>6.5 cm diameter) and postdeployment migration are poor prognostic signs and associated with increased rates of aneurysm-related morbidity.^6,7 Thus, certain subsets of patients would particularly benefit from effective post-EVAR surveillance, and it is our contention that patients with HN anatomy, defined by neck length of <10 mm, neck angle of 60°, ≥50% circumferential proximal neck thrombus (≥2 mm thick), ≥50% circumferential calcified proximal neck, reverse taper, or a diameter >31 mm, should strictly adhere to surveillance protocols.

To achieve this goal, the SVS established lifelong surveillauce gui<leliues for patients who urn.lergu EVAR.⁸ The guidelines recommend CT scanning at 1 and 12 months during the first postoperative year, with an additional CT scan at 6 months if an abnormality is detected at the first month follow-up. After the first year, CT scanning is recommended every 12 months, with the alternative option of ultrasound imaging if no abnormality is detected during the first year.^8,9 However, some practitioners have limited the use of CT scans in favor of duplex ultrasound evaluation, in whole or in part. Bargellini et al advocated reserving CT after 1year of follow-up in favor of annual ultrasound evaluations.¹⁴ Troutman et al went even further, and proposed replacement of CT with ultrasound evaluation as the primary surveillance tool and indicated that additional ultrasound evaluation could be postponed until 3 years after EVAR if the initial result of surveillance ultrasound is normal.2 Arguments for avoiding CT scans include contrast-induced nephrotoxicity, cumulative radiation exposure, and increased follow-up costs,¹⁵ and the claim that early postprocedure CT scans fail to influence treatment in 99% of cases.¹⁶ At our institution, the postoperative imaging protocol consisted of CT and/or duplex ultrasound with a clinic visit at 30 days and then repeated at 6 and 12 months, followed by yearly evaluations. Over the past few years, this regimen was modified to include CT and/or duplex ultrasound at 30 days postoperatively; if this study was normal, then only duplex ultrasound was performed at 6 and 12 months, then annually. CT was reserved only for patients who showed an endoleak or enlarging aortic sac size.

Despite the SVS-recommended surveillance guidelines, and the logically modified alternative protocols adopted by various practitioners, postoperative EVAR surveillance imaging compliance remains poor . Schanzer et al analyzed 19,962 patients (Medicare beneficiaries) who underwent EVAR and found the incidence of loss to annual imaging follow-up at 1, 3, and 5 )'Cars to be 22%, 38%, and 50%.¹⁰ Jones et al found a 33% noncompliance rate in 302 patients who underwent EVAR at a single institution over an average follow-up of 30 months.¹² The European Collaborating Group on Stent-Graft Techniques for Abdominal Aortic Aneurysm Repair found that 65% of 4433 patients enrolled in their registry between 1996 and 2004 failed to complv with their follow-up regimen.¹⁷ Similarly, Garg et al reported only a 43% surveillance compliance among 9695 patients who received EVAR from 2002 to 2005 and were imaged through 2011.9 Our review of 565 patients echoed these findings, with only a 43% compliance rate with our surveillance protocol.

On the basis of further analysis in various studies, certain subsets of patients appeared to exhibit poorer compliance than others. Patients who underwent EVAR at higher-xvolume centers were independently associated with complete surveillance, and low-volume centers showed higher noncompliance rates and number of patients lost to follow-up.^9,11 Although some authors found geographic factors, such as rural or small-town residence or increased distance to the hospital adversely affected compliance,⁹ others found no difference.^11,18 Urgent or emergent treatment, and EVAR for ruptured AAA, were found to be significant factors for compliance failure and loss to follow-up in studies by Schanzer et al¹⁰ and Garg et al.⁹ Other medical comorbidities, such as congestive heart failure, cerebrovascular disease, chronic obstructive pulmonary disease, chronic renal insufficiency, diabetes, and cancer also significantly contributed to poor compliance.^9,10 In our study, peripheral artery disease, carotid artery disease, and patients with HN anatomy appeared to adversely affect compliance; however, after multivariate analysis, only patients with carotid artery disease or HN anatomy showed statistical significance. Age was not a factor in compliance in our series.

Speculation as to why compliance remains poor has been oftered by various authors. Some believe that fear of contrast nephrotoxicity or the cumulative effects of radiation might discourage patients from undergoing repetitive CT evaluations.^15,19,21 With regard to EVAR treatment for ruptured AAA or urgent and/or emergent AAA treatment with EVAR, patients might be treated far from their residence, and travel distance to these treatment centers after discharge for surveillance might be overly burdensome.^9,10 Others might obtain treatment outside of their established health care network and simply become Jost to follow-up. Also, patients who ultimately suffer a ruptured AAA might have had poor surveillance to begin with, which would thus contribute to rupture rather than a timely intervention.⁹ Others believe that patients with multiple comorbidities are usuallv followed closer by physicians and perhaps have a higher chance of incorporation of aneurysm surveillance as part of a more rigorous, more frequent follow-up regimen because of their complexity of ailments.^9,10

Recently, some authorities recommended some modifications of post-EVAR surveillance. Nordon et al¹⁵ reported on secondary intervention and surveillance imaging rates, and reported the evidence to support modified EVAR surveillance programs. They conducted a systematic review of the literature between 2002 and 2009 and a meta-analysis of Kaplan-Meier reintervention-free survival rates. Their analysis included 32 studies (17,987 EVAR cases). The crude annual secondary intervention rates from U.S. population registries were 3.7% per year (range, 1.7%-4.3%). The combined reintervention-free survival rates from 14 series (10,365 cases) demonstrated a linear progression with 90%, 87%, and 82% of grafts without secondary procedures at 2, 3, and 5 years, respectively. Surveillance imaging alone initiated secondary interventions in 1.4% to 9% of cases, and >90% of EVAR cases received no benefit from surveillance. They believe that some form of surveillance after EVAR is necessary, despite a reduction in secondary interventions with use of modern stent grafts. They concluded that EVAR surveillance should be targeted at stent grafts and patients at high risk of complications.

Sternbergh et al²² reported on redefining postoperative surveillance after EVAR and their recommendations based on a 5-year follow-up in the United States Zenith multicenter trial. They raised several concerns regarding post-EVAR surveillance, such as radiation exposure, effect on renal function, and the significant cost incurred. They analyzed 739 patients who underwent EVAR as part of a prospective multicenter pivotal (phase II) and continued-access (phase III) U.S. Zenith Endovascular graft trials. They concluded that the absence of endoleak at 30 days and 1 year predicted greatly improved long-term freedom from aneurysm-related morbidity, compared with early endoleak. A modified EVAR surveillance protocol was recommended, which modulates the frequency and intensity of post-EVAR imaging based on these early outcomes. They believe that in patients without early endoleak, the 6-month surveillance can be eliminated and aortic ultrasound is suggested for long-term surveillance over 1 year. This modified surveillance protocol would be sufficient in most patients and could improve patient safety by reducing the negative effects of radiation exposure and contrast, while also reducing costs.

Finally, on the basis of the findings of our study, we are presently discussing the possibility of adding a designated full-time employee to assist patients in compliance with their follow-up visits and receipt of their post-EVAR imaging.

This study has limitations, including its being a retrospective analysis, therefore, these results should be interpreted cautiously. A significant number of the devices were Gore Excluder (n = 304) or Zenith (n = 108) with a lesser number of other devices, which might yield different clinical outcomes, particularly with a different follow-up time frame. Other factors that might affect surveillance is the type of insurance, however, most of our patients had Medicare and/or Medicaid. There is also a lack of a consistent definition of adequate post-EVAR surveillance compliance in the literature.

CONCLUSIONS

The overall patient compliance rate for post-EVAR imaging surveillance was low, particularly in EVAR patients with HN anatomy. However, additional studies are needed to verify if strict post-EVAR surveillance is necessary and to determine its effect on long-term clinical outcome.

The authors gratefully acknowledge Mary Emmett, PhD for her assistance and Mona Lett for her editorial assistance in the preparation of this report.