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Corresponding author. Amsterdam UMC, University of Amsterdam, Amsterdam Cardiovascular Sciences, Department of Surgery, Meibergdreef 9, 1105 AZ, Amsterdam, the Netherlands.
The new 2019 guideline of the European Society for Vascular Surgery (ESVS) recommends consideration for elective iliac artery aneurysm (eIAA) repair when the iliac diameter exceeds 3.5 cm, as opposed to 3.0 cm previously. The current study assessed diameters at time of eIAA repair and ruptured IAA (rIAA) repair and compared clinical outcomes after open surgical repair (OSR) and endovascular aneurysm repair (EVAR).
Methods
This retrospective observational study used the nationwide Dutch Surgical Aneurysm Audit (DSAA) registry that includes all patients who undergo aorto-iliac aneurysm repair in the Netherlands. All patients who underwent primary IAA repair between 1 January 2014 and 1 January 2018 were included. Diameters at time of eIAA and rIAA repair were compared in a descriptive fashion. The anatomical location of the IAA was not registered in the registry. Patient characteristics and outcomes of OSR and EVAR were compared with appropriate statistical tests.
Results
The DSAA registry comprised 974 patients who underwent IAA repair. A total of 851 patients were included after exclusion of patients undergoing revision surgery and patients with missing essential variables. eIAA repair was carried out in 713 patients, rIAA repair in 102, and symptomatic IAA repair in 36. OSR was performed in 205, EVAR in 618, and hybrid repairs and conversions in 28. The median maximum IAA diameter at the time of eIAA and rIAA repair was 43 (IQR 38–50) mm and 68 (IQR 58–85) mm, respectively. Mortality was 1.3% (95% CI 0.7–2.4) after eIAA repair and 25.5% (95% CI 18.0–34.7) after rIAA repair. Mortality was not significantly different between the OSR and EVAR subgroups. Elective OSR was associated with significantly more complications than EVAR (intra-operative: 9.8% vs. 3.6%, post-operative: 34.0% vs. 13.8%, respectively).
Conclusion
In the Netherlands, most eIAA repairs are performed at diameters larger than recommended by the ESVS guideline. These findings appear to support the recent increase in the threshold diameter for eIAA repair.
The new 2019 guideline of the European Society for Vascular Surgery recommends consideration for elective iliac artery aneurysm (IAA) repair when the iliac diameter exceeds 35 mm. This nationwide study from the Netherlands demonstrates that elective IAA repair is carried out at a median maximum diameter of 43 mm, and ruptured IAA repair at 68 mm. The findings appear to support the recent raise of the threshold diameter for elective IAA repair.
Introduction
Iliac artery aneurysm (IAA) is a condition that accounts for a small proportion of all intra-abdominal aneurysms. Approximately 20% of patients with abdominal aortic aneurysms (AAAs) have concomitant IAA.
Like AAAs, IAAs are often operated on electively to prevent future rupture. The introduction of endovascular aneurysm repair (EVAR) has resulted in a significant increase in elective IAA (eIAA) repair in recent years.
No IAA specific trials have been conducted to date. The small body of evidence regarding IAA management is in sharp contrast to that of AAA. Outcomes after AAA repair are well known and trials have demonstrated that it is safe to wait for elective AAA repair in men until a maximum diameter of 5.5 cm is reached.
With respect to IAA, the clinical outcomes of patients have not been described extensively and there is no solid evidence with regard to a threshold diameter for elective repair. The recent 2019 guideline on abdominal aorto-iliac artery aneurysms from the European Society for Vascular Surgery (ESVS) recommended consideration for eIAA repair when the iliac artery diameter exceeds 3.5 cm.
The recommended diameter in the previous guideline was 3.0 cm. The new recommendation is based on evidence of low quality (level C) and does not make a distinction between aneurysms of the common, external, or internal iliac artery (CIA, EIA, IIA, respectively). Others have suggested that the threshold diameter for eIAA repair should be raised to 4 cm.
In this study, the Dutch Surgical Aneurysm Audit (DSAA) registry was used to evaluate the indications for and outcomes of IAA surgery at a national level in the Netherlands.
The primary study objective was to determine the maximum IAA diameters at time of eIAA and ruptured IAA (rIAA) repair. Other objectives were to present clinical outcomes after IAA repair, to compare outcomes after open surgical repair (OSR) and EVAR, and to determine risk factors for post-operative mortality.
Materials and Methods
Study design and setting
This retrospective observational study used prospectively collected data from the DSAA registry, which is a nationwide prospective registry of all patients undergoing aortic or iliac aneurysm repair in the Netherlands. DSAA is one of the healthcare registries of the Dutch Institute of Clinical Auditing.
Registration of patients in the DSAA registry is mandatory for all hospitals carrying out aneurysm repair. Vascular surgeons prospectively register patients and their characteristics and outcomes in this registry. The scientific board of DSAA approved the study protocol (DSAA201707) prior to release of the data. According to Dutch law, patient consent and approval by an ethics committee was not required because the data were anonymised. The study included patients who underwent repair between 1 January 2014 and 1 January 2018. This inclusion period was chosen because the registration of patients undergoing IAA repair was initiated in 2014. The last data verification of the DSAA registry was performed for the items “mortality,” “complications,” “re-interventions,” and “readmissions” in 2016.
All patients who were registered in the DSAA for primary IAA repair were eligible for inclusion. Therefore, no sample size calculation was carried out. Patients were excluded when they underwent revision surgery (e.g. late conversions), or when predefined variables labelled as essential were missing. These essential variables were age, sex, repair method (i.e. OSR, EVAR), and repair urgency (elective, ruptured, or symptomatic non-ruptured IAA). Patients undergoing conversions during initial repair were included.
Endpoints
The IAA diameter was registered as the maximum diameter (in mm) without specification of the imaging modality used. Post-operative mortality was defined as the combined 30 day and in hospital mortality. Definitions of the post-operative complications are listed in Table S1. Baseline patient characteristics and comorbidities were registered in the DSAA in accordance with the categorisations of the Physiological and Operative Severity Score for the enUmeration of Mortality and morbidity (POSSUM), a mortality risk prediction model for surgical patients.
The anatomical location of the IAA (CIA, EIA, or IAA) was not registered in the DSAA and could not be analysed.
The results were also compared with a recent DSAA study (of 1331 men with ruptured AAA) to compare the number of aneurysms that undergo ruptured repair below the threshold diameter.
A registry-based rationale for discrete intervention thresholds for open and endovascular elective abdominal aortic aneurysm repair in female patients.
That study demonstrated that 8% of AAAs were operated on for rupture below the threshold diameter of 5.5 cm. The eighth percentile was translated to the current cohort of ruptured IAAs to find an IAA equivalent diameter.
Statistical analysis
Missing data were not imputed. Categorical data are reported as numbers and percentages with 95% confidence intervals (CI). Normally distributed continuous data are reported as mean ± standard deviation (SD). Data with skewed distribution are reported as median with interquartile range (IQR). Differences between patients undergoing OSR and EVAR were tested with the Fisher's exact test for categorical variables, and with the unpaired t test or Mann–Whitney U test for continuous variables. The test choice was based on the data distribution, which was tested with the Shapiro–Wilk test. Risk factors for post-operative death were identified by applying the same method. Differences were calculated between patients who did and did not survive the hospital stay. This was done separately for both eIAA and rIAA repair. A multivariable logistic regression analysis was not carried out because the absolute mortality numbers were low, and because some baseline variables were so rare that odds ratios could not be calculated or were accompanied by very wide CIs. All statistical analyses were carried out using IBM SPSS Statistics version 24 (IBM Inc., Armonk, NY, USA). A p value of < .050 was considered to be statistically significant.
Results
Participants
The DSAA registry database contained 974 patients who underwent IAA repair between 1 January 2014 and 1 January 2018. Eight hundred and fifty-one patients were included in this study after exclusion of 119 patients who underwent revision surgery, and four patients with missing essential variables (age, sex, repair method and repair urgency, in one respectively). Some 91% of patients (n = 778) were male and the mean age was 71.6 ± 8.9 years (Table 1). The aetiology of the IAAs was reported as atherosclerotic (n = 432), inflammatory (n = 6), infectious (n = 9), dissection (n = 9), trauma (n = 3), connective disorder (n = 13), unknown (n = 45), and missing (n = 334). Other patient characteristics are listed in Table S2.
Table 1Characteristics of 851 patients registered in the nationwide Dutch Surgical Aneurysm Audit (DSAA) registry for primary iliac artery aneurysm (IAA) repair
Patient characteristics
Total (n = 851)
Elective (n = 713)
Rupture (n = 102)
Symptomatic (n = 36)
Total missing
Age – years
71.6 ± 8.9 72 (66–78)
71.2 ± 8.7 72 (66–77)
74.0 ± 8.5 74 (68–81)
71.3 ± 12.9 73.5 (66–80)
0
Male sex
778 (91.4)
656 (92.0)
91 (89.2)
31 (86.1)
0
Cardiac disease
447 (53.7)
378 (53.7)
50 (53.8)
19 (54.3)
19
Pulmonary disease
173 (20.9)
153 (21.6)
13 (14.6)
7 (21.9)
23
Pre-operative serum creatinine – μmol/L
103.5 ± 61.6 90 (77–110)
99.9 ± 60.5 88 (76–105)
127.4 ± 56.7 116 (93–150)
107.9 ± 81.1 89 (77–116)
23
IAA diameter – mm
Total
48.6 ± 15.5 45 (38–54)
45.4 ± 11.5 43 (38–50)
69.0 ± 21.5 68 (58–85)
60.4 ± 21.2 60 (42–75)
20
EVAR
47.6 ± 14.1 45 (39–52)
45.2 ± 10.5 43 (38–50)
67.6 ± 22.3 61 (58–84)
61.0 ± 22.5 58 (43–74)
16
OSR
52.2 ± 18.7 48 (38–64)
46.6 ± 14.4 45 (37–52)
72.3 ± 19.7 71 (60–87)
59.0 ± 19.0 65 (38–78)
4
Repair method
EVAR
618 (72.6)
536 (75.2)
57 (55.9)
25 (69.4)
0
OSR
205 (24.1)
154 (21.6)
40 (39.2)
11 (30.6)
0
Other
28 (3.3)
23 (3.3)
5 (4.9)
0
0
Data are provided as n (%) and, for continuous variables, as mean ± standard deviation and median (interquartile range). EVAR = endovascular aneurysm repair; OSR = open surgical repair.
A total of 713 patients (84%) underwent eIAA repair, 102 underwent rIAA repair, and 36 underwent symptomatic IAA (sIAA) repair. The method of repair was OSR in 205 patients, EVAR in 618 (including 100 iliac branched devices), and other methods in 28 (12 hybrid repairs, five primary conversions and 11 others). Patients undergoing rIAA repair were significantly older than patients undergoing eIAA repair (median 74 vs. 72 years, respectively; Table 1; p = .007). Patients who underwent EVAR were treated with Medtronic (n = 229), Gore (n = 196), Cook (n = 92), Vascutek (n = 38), Endologix (n = 30), and other (n = 33) devices.
Main outcomes
IAA diameter at time of repair
Elective IAA repair
Diameter data was available for 706 of 713 patients undergoing eIAA repair. The median maximum IAA diameter of 706 patients was 43 (IQR 38–50) mm. The diameters were not significantly different between the OSR and EVAR subgroups (45 mm vs. 43 mm in 152 and 531 patients, respectively, p = .47; Table 1). Seventy-two of 706 IAAs (10.2%) were smaller than 35 mm at time of elective repair (Fig. 1, Table S3).
Figure 1Distribution of iliac artery aneurysm (IAA) diameter at time of elective (n = 706) and ruptured IAA repair (n = 90) in patients registered in the nationwide Dutch Surgical Aneurysm Audit (DSAA) registry. The distribution is additionally listed in Table S3. SD = standard deviation; IQR = interquartile range.
Diameter data was available for 90 of 102 patients undergoing rIAA repair. The median maximum diameter of 90 patients was 68 (IQR 58–85) mm and was not significantly different between the OSR and EVAR subgroups (71 mm vs. 61 mm in 38 and 47 patients respectively, p = .31). At the time of rupture, four of 90 IAAs (4.4%) were <30 mm, three IAAs (3.3%) were 30–34 mm, and two IAAs (2.2%) were 35–39 mm (Fig. 1, Table S3). IAA diameters were significantly larger at the time of rupture than at the time of elective repair (p < .001).
Sex differences
Diameters at the time of surgery were not different between men and women, both for eIAA repair (median 43.0 mm vs. 42.5 mm, in 650 and 56 patients respectively, p = .41), and for rIAA repair (median 68.5 vs. 63.0 mm, in 80 and 10 patients respectively, p = .72).
Comparison with AAA
A recent study with DSAA data demonstrated that 8% of AAAs underwent ruptured repair below the threshold diameter of 5.5 cm.
A registry-based rationale for discrete intervention thresholds for open and endovascular elective abdominal aortic aneurysm repair in female patients.
The translation of that eighth percentile to the current cohort of 90 ruptured IAAs revealed an IAA equivalent diameter of 34 mm (Table S3).
Post-operative outcomes
Elective IAA repair
Mortality was 1.3% (9/713; 95% CI 0.7–2.4%) after eIAA repair and was not significantly different between the OSR and EVAR subgroups (2.6% vs. 0.9% respectively; p = .12). Complications occurred significantly more often after OSR (intra-operative complications: 9.8% vs. 3.6%, p = .005; post-operative complications: 34.0% vs. 13.8%, p < .001). In total, 197 post-operative complications occurred in 130 patients (Table 2). The most frequent complications were arterial occlusions (in 25) and abdominal and pulmonary complications (both in 23). The number of hospital admission days was significantly higher after OSR (median 7 vs. 2 days; p < .001). Similar differences between OSR and EVAR were observed for ICU admission days (p < .001) and re-intervention rates (p = .003; Table 2).
Table 2Post-operative outcomes after iliac artery aneurysm (IAA) repair by open surgical repair (OSR) or endovascular aneurysm repair (EVAR) in patients registered in the nationwide Dutch Surgical Aneurysm Audit (DSAA) registry
The “Total” columns also include methods of repair other than open surgical repair (OSR) and endovascular aneurysm repair (EVAR) (i.e. hybrid repair and primary conversion).
The “Total” columns also include methods of repair other than open surgical repair (OSR) and endovascular aneurysm repair (EVAR) (i.e. hybrid repair and primary conversion).
The “Total” columns also include methods of repair other than open surgical repair (OSR) and endovascular aneurysm repair (EVAR) (i.e. hybrid repair and primary conversion).
Data are provided as n (%) and, for continuous variables, as mean ± standard deviation and median (interquartile range). ICU = intensive care unit.
∗ The “Total” columns also include methods of repair other than open surgical repair (OSR) and endovascular aneurysm repair (EVAR) (i.e. hybrid repair and primary conversion).
† The sum of complications is more than the number of patients with complications.
Mortality after rIAA repair was 25.5% (26/102; 95% CI 18.0–34.7%). The difference between OSR and EVAR was not statistically significant (32.5% vs. 17.5% respectively, p = .097). A total of 100 post-operative complications occurred in 57 patients. Intra- and post-operative complication rates were not statistically different between the OSR and EVAR subgroups, however, the number of hospital admission days was significantly higher after OSR (median 10 vs. 7 days, p = .003). Outcomes after symptomatic (non-ruptured) IAA repair are also listed in Table 2. The small number of patients and events in the male and female subgroups did not allow other statistical assessments of mortality differences between men and women (Table S4).
Risk factors for mortality
None of the available baseline patient characteristics or pre-operative measurements was associated with mortality after eIAA repair. The single measurement significantly associated with mortality after rIAA repair was pre-operative serum creatinine (p = .003) (Table S5).
Discussion
This nationwide analysis of surgery for IAA in the Netherlands demonstrated that elective IAA repair was carried out at a median maximum diameter of 43 mm. IAAs ruptured at a median maximum diameter of 68 mm. Mortality was 1.3% after elective repair and 25.5% after ruptured IAA repair. Mortality was not significantly different between the OSR and EVAR subgroups. Patients undergoing elective OSR suffered from significantly more intra- and post-operative complications than patients undergoing elective EVAR.
With a median IAA diameter of 43 mm at the time of elective repair, most patients in the Netherlands are electively operated on when the recommended threshold diameter of 35 mm is exceeded. Currently, only 10% of patients are operated on before the IAA reaches a diameter of 35 mm. As there is no IAA screening programme in the Netherlands, this could either be the consequence of IAA detection at late stages, or because of conservative surgical management of Dutch surgeons. Yet, this outcome is in line with practice in other countries. Boules et al. reported a mean diameter of 42 mm at time of elective repair in the United States between 1995 and 2004.
More recently, a survey among vascular surgeons from the United Kingdom revealed that two thirds of surgeons would wait until a CIA aneurysm reached 40 mm in diameter before considering elective repair.
The large difference between IAA diameter at time of eIAA and rIAA repair supports the recent raise of the threshold diameter from 3.0 to 3.5 cm by the ESVS.
As listed in Table S3, three iliac artery aneurysms ruptured between 30–34 mm (over the course of four years). This would mean that approximately one additional patient per year would undergo ruptured IAA repair per year in the Netherlands if a threshold diameter of 3.5 cm was applied. The raise of the threshold diameter to 3.5 cm is also supported by comparison of the present study with a recent AAA study, which resulted in an IAA equivalent diameter of 34 mm.
A registry-based rationale for discrete intervention thresholds for open and endovascular elective abdominal aortic aneurysm repair in female patients.
The implementation of a 34 mm threshold for eIAA repair would result in 8% of patients with IAA undergoing ruptured repair below the threshold diameter. That would be equal to the currently accepted risk of rupture for AAA. This comparison between IAA and AAA only serves for hypothesis generating purposes, and is only valid if the ratio between operation risk and rupture risk is similar for IAA and AAA, and if detection rates for AAA and IAA are similar – in the absence of an AAA or IAA screening programme. With regard to the operation risk, the peri-operative mortality in the present study was 2.6% and 0.9% after elective OSR and EVAR, respectively, which is slightly lower than the short term mortality of 5.0% and 0.9% after elective OSR and EVAR for AAA in the Netherlands.
These studies did not detect sufficient ruptures to allow assessment of rupture risk. Another reason for the relatively large diameters at time of elective IAA repair in the Netherlands could be that IAAs are detected at late stages. After all, there is no AAA or IAA screening programme in the Netherlands, and asymptomatic IAAs can be difficult to detect clinically.
With regard to EVAR, post-operative mortality was around 1%, and patients had significantly fewer complications and shorter hospital admissions compared with OSR. The present findings correspond to results from previous studies. Buck et al. consulted the Nationwide Inpatient Sample database from the United States (with 9016 elective EVARs for IAA) and demonstrated an in hospital mortality of 0.5%, a complication rate of 6.7%, and a median hospital stay of 2.3 days after elective EVAR for isolated IAA.
However, as long term outcomes after IAA repair are largely unknown, it remains premature to suggest an EVAR first policy for all patients with suitable anatomy.
Strengths and limitations
The strength of this study lies in the large sample size and the national coverage. It is the largest study to date that has reported diameters at time of IAA repair. Nevertheless, this study is subject to some major limitations. As with other retrospective studies using administrative databases, there is a possibility of coding errors and missing data. The last data verification of DSAA from 2016 was also limited by the small number of verified data items (only four), and the small number of hospitals participating in the verification (14 of 60). Furthermore, the included patients were registered for undergoing primary IAA repair, and not for undergoing isolated IAA repair. Therefore, the proportion of patients undergoing concomitant AAA repair is unknown. Another limitation was that DSAA only consists of patients who have undergone repair. Diameters at time of rupture are therefore unknown for patients who were not operated on for ruptured IAA. Moreover, patients with aorto-iliac aneurysms who were primarily operated on for AAA are not included in this analysis. Therefore, the diameters at the time of IAA repair may be subject to bias. In addition, the method of diameter measurement was not standardised. As a consequence, it was unclear which diameters were based on ultrasound measurements and which on CT measurements. Considering the measurement variation between ultrasound and CT, this is an important limitation. Moreover, diameter data were not available for 12 of 102 patients undergoing ruptured repair and for seven of 713 undergoing elective repair. The non-availability of some relevant and interesting data was another limitation. This prevented characterisation of the cohort in more detail. The most important non-available variable was the aneurysm location, namely CIA, EIA, or IIA. CIAs with normal anatomy have diameters that are two times larger than the IIA.
Ideally, the suggested threshold diameter would be tailored to aneurysms of specific iliac locations. Unfortunately, the present study could not make this anatomic distinction, similar to the ESVS guideline that only provided recommendations for IAA in general.
Other items such as pseudoaneurysms, complications such as buttock claudication, or level of care needed after discharge also were not available in the registry. The aetiology of the IAA was missing in many cases (n = 334). Another limitation was posed by the low absolute mortality rates and some infrequent baseline variables (Table S2). As a consequence, only one baseline characteristic was identified (i.e. serum creatinine prior to rIAA repair) that was significantly associated with post-operative mortality. In addition, it was not possible to carry out a multivariable logistic regression analysis that could identify independent risk factors for mortality. Furthermore, the DSAA only contains outcomes up to 30 days after IAA repair. Mid and long term outcomes for this cohort are therefore unknown. Information on endoleaks, graft patency, and re-interventions is needed to determine all benefits and harms of OSR and EVAR, which in turn are needed to determine the best treatment strategy for patients with IAA.
Future perspectives
As no IAA specific trials are expected in the near future, evidence for clinical management comes from the results of observational studies. Large registries that include both post-operative outcomes and IAA diameters could provide data for these future studies. With statistical methods such as standardisation or inverse probability weighting, trials can be mimicked to estimate causal effects.
Yet, this would require a larger volume of patient specific data than available for the current study. Furthermore, considering the positive outcomes after EVAR, more research should be conducted on improving EVAR suitability. Future studies should also investigate the long term outcomes after IAA repair, and EVAR specifically– as the long term outcomes after IAA repair are unknown.
Acknowledgements
The authors thank all collaborators of the Dutch Society for Vascular Surgery (NVvV) who registered the patients and outcome data in the DSAA database (see Appendix S1).
Conflict of Interest
None.
Funding
This work was supported by the AMC Foundation, which was not involved in the conduct of this study.
Appendix A. Supplementary data
The following is the Supplementary data to this article:
A registry-based rationale for discrete intervention thresholds for open and endovascular elective abdominal aortic aneurysm repair in female patients.
The decision to operate on an asymptomatic patient with an aorto-iliac aneurysm is multifactorial, with rupture risk being an important piece of a complex equation. We recognise that diameter is a relatively poor predictor of rupture, but epidemiological studies have long established that it is reasonably safe to observe small aneurysms, while large ones tend to rupture and repair should be considered. High quality, level A evidence has been published supporting the conservative management of men with abdominal aortic aneurysms <55 mm.
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