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This study aimed to analyse the mean abdominal aortic aneurysm (AAA) diameter for repair in nine countries, and to determine variation in mean AAA diameter for elective AAA repair and its relationship to rupture AAA repair rates and aneurysm related mortality in corresponding populations.
Data on intact (iAAA) and ruptured infrarenal AAA (rAAA) repair for the years 2010–2012 were collected from Denmark, England, Finland, Germany, Hungary, New Zealand, Norway, Sweden, and the USA. The rate of iAAA repair and rAAA per 100 000 inhabitants above 59 years old, mean AAA diameter for iAAA repair and rAAA repair, and the national rates of rAAA were assessed. National cause of death statistics were used to estimate aneurysm related mortality. Direct standardisation methods were applied to the national mortality data. Logistic regression and analysis of variance model adjustments were made for age groups, sex, and year.
There was a variation in the mean diameter of iAAA repair (n = 34 566; range Germany = 57 mm, Denmark = 68 mm). The standardised iAAA repair rate per 100000 inhabitants varied from 10.4 (Hungary) to 66.5 (Norway), p<.01, and the standardised rAAA repair rate per 100 000 from 5.8 (USA) to 16.9 (England), p<.01. Overall, there was no significant correlation between mean diameter of iAAA repair and standardised iAAA rate (r2 = 0.04, p = .3). There was no significant correlation between rAAA repair rate (n = 12 628) with mean diameter of iAAA repair (r2 = 0.2, p = .1).
Despite recommendations from learned society guidelines, data indicate variations in mean diameter for AAA repair. There was no significant correlation between mean diameter of AAA repair and rates of iAAA repair and rAAA repair. These analyses are subject to differences in disease prevalence, uncertainties in rupture rates, validations of vascular registries, causes of death and registrations.
These studies did not find a statistically significant difference in long term survival between immediate open repair and surveillance for aneurysms < 55 mm in diameter. Two trials performed in the endovascular era, the Comparison of Surveillance vs. Aortic Endografting for Small Aneurysm Repair (CAESAR)
trials, compared immediate EVAR with surveillance for AAAs between 4.1 and 5.4 cm (CAESAR) and 4.0 and 5.0 cm (PIVOTAL) and found no survival benefit for early EVAR. This was confirmed by a Cochrane database review
Furthermore, considerable international variation exists in clinical practice where the proportion of AAAs that are repaired at a diameter of less than 55 mm has been reported to range from 6.4% to 29.0% in various countries.
This highlights the potential equipoise that may exist as to when to offer surgery. The ultimate goal of elective AAA repair is to reduce the risk of rupture and burden of disease in AAA related mortality, but assessment of rupture rate and incidence of aortic rupture mortality is challenging. Studies suggest that increasing the number of small AAA repairs due to a lowered threshold for intact repair will in turn increase the overall denominator, reducing the proportion of patients treated for rAAA even though the incidence of ruptures may remain unchanged.
This study aimed to analyse the practice of AAA repair in different European and non-European countries, to determine variation in mean AAA diameter for iAAA repair and its impact on corresponding aneurysm related mortality.
The guidelines by learned societies recommend that for men, intervention should be considered for an intact abdominal aortic aneurysm (AAA) once the maximum diameter reaches 55 mm. This study highlights the variation in the mean diameter of intact AAA repair when nine different European and non-European countries were analysed. However, there were no significant correlations between AAA size at the time of intact repair and rupture AAA repair rates or death from ruptured AAA across the participating countries. Thus this study does not validate previous reports suggesting that a lower mean diameter at time of intact AAA repair would reduce AAA related mortality at a national level.
Materials and methods
This project was carried out in collaboration with the VASCUNET quality improvement network of the European Society for Vascular Surgery (ESVS). Data on iAAA and rAAA between 1 January 2010 and 31 December 2012 were collected from nine countries (Denmark, England, Finland, Germany, Hungary, New Zealand, Norway, Sweden, and USA). Ethics approval was obtained for this analysis as required based on national regulations for participating countries, who provided the following data:
In hospital data for infrarenal iAAA and rAAA repair. Data collected involved the age, gender, date of surgery, AAA diameter at repair and in hospital death (pre-discharge) or within 30 days of surgery.
National rAAA mortality data using the International Classification of Diseases, 10th Revision (ICD-10) codes I71.3 and I71.8 and on iAAA using the ICD-10 codes I71.4 and I71.9.
In hospital data source
In hospital data were provided from vascular registries or administrative data (hospital episode statistics) when not available. These registries consisted of national (Denmark, Hungary, New Zealand, Norway, Sweden, England), regional (Finland), and multicentre (Germany, USA) databases. The estimated coverage of the participating vascular registries was > 90% for aortic procedures performed in Denmark, Hungary, New Zealand, Sweden, England, and the Helsinki region in Finland, and 80% in Norway. The German data were based on population based hospital episode statistics. Data on diameter in Denmark were provided as aggregate mean for the years 2014–2016. US data were obtained from National Surgical Quality Improvement Program (NSQIP) for period 1 January 2011 till 31 December 2012.
Data source for aneurysm related mortality
Data on the frequency of aneurysm related deaths during the period from 2010 through 2012 in the USA were obtained from the Centers for Disease Control and Prevention (CDC) (www.cdc.gov), and data in England were obtained from the Office of National Statistics (www.ons.gov.uk). Data from Germany were obtained from causes of death statistics of the Federal Statistical Office (www.destatis.de). Data from European Countries were obtained from Eurostat (http://ec.europa.eu/eurostat) while data from New Zealand was obtained from the Ministry of Health Mortality Collection.
The primary outcome of the study was to determine whether the mean iAAA diameter correlates with the rAAA repair rate. The secondary outcomes of the study were to determine whether the mean iAAA repair diameter is related to the nations' standardised rAAA incidence rate. The national rAAA rate was determined by combining the number of patients surviving rAAA repair and the number of deaths due to rAAA (including deaths after attempt at rAAA repair) based on the data on aneurysm related mortality per country. Gender adjusted population for older than 59 years per country was used as the denominator for calculation of all incidence rates per 100 000 inhabitants. Subgroup analyses were carried out to analyse the effect of gender on outcome. For subgroup gender analysis, data from Germany and Denmark were not available (i.e. data provided was a combination with no identifier) while data from Norway could not be standardised by age of patients.
Direct standardisation methods were applied to the national mortality data using the over 59 year old English population in 2012 (obtained from Office of National Statistics) as a reference. This was done to enable comparison of the results with other published studies using the English population.
Logistic regression models were applied based on country frequency data by 10 year age groups, sex, and year. An analysis of variance model was fitted to look at the differences in mean AAA diameter at the time of repair between countries, adjusted by age groups and gender. A p value < .05 was regarded as statistically significant. Statistical analysis was carried out using SAS version 9.4 (SAS Institute, Cary, NC, USA) and R 3.3.2 (R Foundation for Statistical Computing, Vienna, Austria).
To avoid analysing data with potential erroneous AAA diameter values, AAA diameter ≤ 20 mm and ≥ 150 mm were excluded from the analyses (38 patients). Missing AAA diameter values (105 patients) were handled by case deletion.
During the period 2010–2012 there was a variation in the mean diameter of iAAA repair across the countries (n = 34 566; range from 57 mm in Germany to 68 mm in Denmark) (Table 1). A variation in the percentage of male patients operated on for AAA with a diameter < 55 mm and female patients operated on with a diameter < 52 mm (to account for previous version guidelines
= 0.1, p = .1). The standardised iAAA repair rate per 100 000 inhabitants varied from 10.4 (Hungary) to 66.5 (Norway), p <.01, and the standarised rAAA repair rate per 100 000 from 5.8 (US) to 16.9 (England), p <.01. The standardised rates of iAAA and rAAA repair per country are presented in Table 1. Overall, despite an apparent higher rate of iAAA repair in countries where iAAA was operated at a lower mean diameter, there was no statistically significant correlation (Fig. 1) (r2 = 0.04, p = .3). Similarly, there was no significant correlation towards lower rates of rAAA repair (n = 12 628) with decreasing mean diameter of iAAA repair (Fig. 1) (r2 = 0.2, p = .1). These results persisted when analysing the national rAAA rate (rAAA repairs + deaths due to rAAA) per country (Fig. 2).
Table 1The intact abdominal aortic aneurysm (iAAA) and ruptured abdominal aortic aneurysm (rAAA) standardised repair rates and the mean diameter of iAAA repair per participating country
When stratifying the results based on gender, similar observations were noted in male patients (Table 2, Table 3, and Fig. 3). However for female patients, in countries where the mean diameter of iAAA repair was smaller (i.e. closer to 55 mm), there was a statistically significant correlation towards higher incidence of iAAA repair (r2 = 0.8 p = .005) (Table 4, Table 5, and Fig. 4).
Table 2Intact abdominal aortic aneurysm (iAAA) and ruptured abdominal aortic aneurysm (rAAA) standardised repair rates and the mean diameter of iAAA repair per participating country in male patients
Mean iAAA diameter – mm
Number of patients with AAA diameter
iAAA standardised repair rate (per 100 000 male inhabitants)
rAAA standardised repair rate (per 100 000 male inhabitants)
Table 3Intact abdominal aortic aneurysm (iAAA) standardised repair rates and standardised national ruptured abdominal aortic aneurysm (rAAA) rate and the mean diameter of iAAA repair per participating country in male patients
Mean iAAA diameter – mm
iAAA standardised repair rate (per 100 000 male inhabitants)
Table 5Intact abdominal aortic aneurysm (iAAA) standardised repair rates and standardised national ruptured abdominal aortic aneurysm (rAAA) rate and the mean diameter of iAAA repair per participating country in female patients
which showed that in the USA, where more iAAAs were carried out at a mean diameter closer to 55 mm, there was a higher rate of iAAA repair and fewer aneurysm related deaths compared with England. Reasons for this could be that when analysing just two countries, differences in coding systems, AAA national reporting methods, AAA prevalence, population structure, and healthcare expenditure may contribute to the stark differences.
Thus, the effects mentioned could be less influential when analysing more countries as in the current analysis. Furthermore, the two outliers with national mean of iAAA diameter < 60 mm (USA and Germany) have a fee for service re-imbursement system while the other six countries have population based re-imbursement further highlighting potential confounders. This could potentially be due to an increased rate of imaging resulting in an increased rate of diagnosis and potentially repair rate.
This study also shows that despite the recommended threshold of 55 mm for elective AAA repair, the mean diameter of AAA at time of repair was 59 mm in females and 62 mm in males. There are several reasons why the mean diameter at the time of repair is higher than the recommended threshold for repair. Only Sweden and England offer AAA screening to men aged 65 and above, while in the USA screening is offered to Medicare men aged 65–75 years who have smoked, thereby patients may remain undiagnosed until they present with incidental AAA at a larger diameter. However, screening in Sweden started in the County of Uppsala in 2006 and reached nationwide cover in 2015,
As a result, the data presented in this study (including data from England, Sweden, and the USA) may not reflect analysis influenced by screening as screening needs a minimum of six to ten years for any benefit in reduction in rAAA.
Thus, the larger than recommended mean diameter of iAAA repair may partly be due to lack of screen detected AAA. Clinicians may also increase the individual threshold for iAAA repair to 60 mm or more in elderly patients or those with important co-morbidities or technically challenging aneurysms, in order to balance the increased peri-operative risk against the risk of rupture.
Another potential reason for the variation in mean diameter may be partially explained by the imaging modality used to capture the size of iAAA in the registries. The diameter of large AAAs obtained through computed tomography scans are usually larger than those obtained by ultrasound;
however, the registries do not state the imaging modality used to capture the AAA diameter. Furthermore, if the data inputted in the registries were captured from the ultrasound findings, there remains no consensus on which aortic boundaries were used to define the diameter (i.e. whether outer, inner, or leading edge, or combinations of these were used). Among those patients who had a screen detected AAA on ultrasound and were referred for surgery once the diameter reached 55 mm, given the difference in AAA size between imaging modalities, the planning computed tomography angiography may result in a larger AAA diameter. This may explain the larger mean diameter than the recommended 55 mm. It was also noted that despite the variation in iAAA repair rate, the percentage of patients operated on with a small AAA (Table S1), age at repair (Table S2), operative modality (Table S3), and variation in the mean iAAA diameter, there was no difference in all cause in hospital death or death within 30 days.
There are several limitations of this study. Data were obtained from a variety of datasets including a population sample (NSQIP). Only the vascular registries of Hungary, Sweden, Denmark, and New Zealand have been internationally validated so far and, as a result, data provided might not be entirely reliable due to potential selection bias.
Another limitation of the study is that due to constraints from registry data including data protection issues, in some countries it was not possible to obtain patient level data from the required time period such as diameter data from Denmark. Furthermore, not all registries covered the whole population, such as the data from Finland which only reflects regional data. Obtaining large numbers of data from different sources, however, may lead to enhanced understanding of the subject and may improve the validity of the data collected through triangulation.
Therefore, the correlation between iAAA repair and rAAA repair rate was chosen as primary endpoint of this study, as registration of rAAA repairs can be expected to be more accurate than rAAA related deaths. However, the results were similar when assessing the correlation between iAAA diameter and rAAA repair rate as well as the national rAAA rate (rAAA operations + rAAA deaths) in this study. Difference in AAA national reporting methods, AAA prevalence, population structure and healthcare expenditure
Other study limitations were that potential different pathologies, including surgery for iliac artery disease and other aortic pathologies may have been included in the study. Despite adjusting for age and gender, it was not possible to adjust for comorbidities, smoking and ethnic/racial differences in different countries.
This study is an analysis of real world evidence of AAA repair practice to determine the impact of mean iAAA repair diameter on corresponding aneurysm related mortality. There was variation in the mean diameter of iAAA repair, iAAA repair rate and rAAA repair rates across countries, however, no significant correlation could be found between mean iAAA diameter at time of repair and rAAA repair rate in different countries.
Data from the National Vascular Registry (England) is based on data collected by or on behalf of the Healthcare Quality Improvement Partnership, who have no responsibility or liability for the accuracy, currency, reliability and/or correctness of this publication.
Appendix A. Supplementary data
The following is the Supplementary data to this article: