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Table of Contents
ORIGINAL ARTICLE
Year : 2020  |  Volume : 3  |  Issue : 4  |  Page : 104-110

Prevalence of abdominal aortic aneurysms and iliac aneurysms in the UK population of 50,000 women


1 Department of Surgery and Cancer; Department of Vascular Surgery, Imperial College, Nicosia, Cyprus
2 Department of Surgery and Cancer, Imperial College; Department of Surgery, University of Nicosia Medical School, Nicosia, Cyprus
3 Department of Surgery and Cancer, Imperial College, Nicosia, Cyprus
4 Wessex Scientific Medical Ultrasound Consultancy, Southampton, UK
5 Department of Metabolism, Digestion, and Reproduction Faculty of Medicine, Imperial College London; Department of Computing, Faculty of Engineering, Imperial College London, London, UK

Date of Submission06-Jul-2020
Date of Decision08-Jul-2020
Date of Acceptance14-Jul-2020
Date of Web Publication24-Dec-2020

Correspondence Address:
Dr. M Chabok
Department Vascular Surgery, Imperial College, London, W12 0HS
Cyprus
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/VIT.VIT_21_20

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  Abstract 


BACKGROUND AND AIMS: Screening men aged 65–80 years for abdominal aortic aneurysm (AAA) is considered economically viable when the prevalence of AAA is 1.0% or higher. Currently, women are not included in AAA screening programs because the prevalence of AAA is <1.0%. The aim of the present analysis is to report (a) the prevalence of AAA ≥3.0 cm or isolated iliac aneurysm (IIA) ≥1.8 cm in women screened with ultrasound (b) the risk factors associated with AAA or IIA in this population, and (c) whether high-risk groups can be identified with an AAA or IIA prevalence of >1.0%.
MATERIALS AND METHODS: Risk factors were collected from 50,000 females who attended for cardiovascular screening. Ultrasound was used to detect the presence of AAA or IIA, the severity of carotid atherosclerosis, and the measurement of ankle/brachial index (ABI). Electrocardiogram (ECG) was used to detect the presence of atrial fibrillation (AF).
RESULTS: Aneurysms were detected in 116 women. Of these aneurysms, 34 (29%) were IIA and 82 were AAA. The presence of AAA or IA below the age of 66 years was rare (10 of 24,499). In the age group of 66–85, there were 102 (0.41%) in 27,170 women, of which 72 were AAA and 30 IIA. By including IIA in the screening protocol for AAA, it became easy to identify subgroups with an aneurysm prevalence >1%. Univariate analysis demonstrated that the presence of any one of the following risk factors, history of myocardial infarction or coronary artery disease, history of stroke/transient ischemic attack (TIA), pack-years ≥10, AF, ABI <0.9, and internal carotid stenosis ≥50% can identify a high-risk group with a prevalence of AAA or IIA >1.0% (range 1.18–2.06). In a multivariable linear logistic regression, age ≥76, hypertension, pack-years, family history of AAA, and history of stroke/TIA were independent predictors for the presence of AAA or IIA. This model had an area under the receiver operator characteristic curve (AUC) of 0.725 (95% confidence interval [CI] 0.673–0.777) and could identify 2947 women who had 41 AAA or IIA present (prevalence 1.39%). By adding ABI and AF, which require a clinical examination and ECG, the receiver operator characteristic (ROC), AUC increased to 0.745 (95% CI 0.693–0.797). This model could identify 3693 women who had 51 AAA or IIA present (prevalence 1.40%). The presence of ≥50% diameter internal carotid stenosis found in 498 women was associated with a prevalence of AAA or IIA of 3.61%, and when added to the model the ROC AUC increased to 0.775 (95% CI 0.724–0.826). This model could identify 3701 women who had 58 AAA or IIA present (prevalence 1.6%).
CONCLUSION: The findings of this study have important implications for developing a screening selection plan for women over 65. By including IIA in the screening protocol for AAA, it became easy to identify subgroups with an aneurysm prevalence >1%. The presence of any one or more of the risk factors listed above can be used to develop targeted screening because of increased risk (>1%). However, whether such screening will be associated with benefits can only be determined by randomized controlled trials and cost-benefit studies.

Keywords: Abdominal aortic aneurysm, prevalence, risk factors


How to cite this article:
Chabok M, Nicolaides A, Aslam M, Farahmandfar M, Humphries K, Kermani N Z, Standfield N. Prevalence of abdominal aortic aneurysms and iliac aneurysms in the UK population of 50,000 women. Vasc Invest Ther 2020;3:104-10

How to cite this URL:
Chabok M, Nicolaides A, Aslam M, Farahmandfar M, Humphries K, Kermani N Z, Standfield N. Prevalence of abdominal aortic aneurysms and iliac aneurysms in the UK population of 50,000 women. Vasc Invest Ther [serial online] 2020 [cited 2021 Jul 27];3:104-10. Available from: https://www.vitonline.org/text.asp?2020/3/4/104/304837




  Introduction Top


Screening for abdominal aortic aneurysm (AAA) using ultrasound followed by surgical intervention when maximum aneurysm diameter reaches 5–5.5 cm reduces mortality by 40% in men aged 65–80-year-old as demonstrated by several randomized studies.[1],[2],[3],[4],[5],[6] Screening is considered economically viable when the prevalence of AAA is 1.0% or higher.[7] Currently, women are not included in AAA screening programs because this is considered as “not indicated or not economically viable.”[8] Epidemiological studies have found that the prevalence of AAA in women is nearly a quarter of that found in men.[9],[10]

Iliac aneurysms are present in 10%–20% of patients with AAA,[11],[12] and their repair is recommended when their diameter exceeds 3–4 cm.[13] Isolated iliac aneurysms (IIAs) were found in 0.03% of 26,251 patients undergoing autopsy.[11] Although IIA are uncommon, their rupture is associated with a 50%–75% mortality.[11]

The prevalence of AAA in 50,000 women in a private, community-based screening program and the risk factors that could identify a subgroup, in which the prevalence of AAA was > 1% was published by our group in 2016.[14] We now report on the prevalence of both AAA and IIA.

The aim of the present analysis is to report (a) the prevalence of AAA ≥3.0 cm or IIA ≥1.8 cm in women screened with ultrasound, (b) the risk factors associated with AAA or IIA in this population, and (c) whether high-risk groups can be identified with a prevalence of AAA or IIA >1%.


  Materials and Methods Top


The material and methodology of this study have already been reported elsewhere.[14] Briefly, participants were screened for preclinical atherosclerotic arterial disease and AAA or IIA through a private, community-based screening program operated by Life Line Screening in the UK and Ireland. Invitations were sent to males and females over the age of 50 years in all UK and Ireland postcodes and regions. Approximately 1% of invitees responded and, together with some younger individuals, decided to take part in this health check program with an attendance rate of 80%. A total of 300,000 men and women were screened. Before the screening, individuals completed consent along with a comprehensive health questionnaire on their demographic information and risk factors for cardiovascular disease. The anonymized database is comprised of 300,000 adult participant records across the UK and Ireland, including both urban and rural populations. For the purpose of this report, we selected the first 50,000 female participants screened between January 2012 and November 2013. Ethical approval was obtained from the Imperial College Research Ethics Committee (ICREC_14_3_7).

Information on age, gender, race/ethnicity, marital status, height, and weight, family history of AAA, coronary artery disease (CAD), stroke, and peripheral vascular disease were collected. Detailed risk factors and comorbidities such as CAD, cerebrovascular disease (previous transient ischemic attack or stroke), hypertension, hypercholesterolemia, and diabetes were included. Patients were considered to have hypertension, hypercholesterolemia, or diabetes if they had been given these diagnoses by a physician or were treated for these conditions. Known cardiovascular disease was defined as having had a prior myocardial infarction (MI), a history of percutaneous or surgical coronary revascularization. A family history of AAA was defined as a first-degree relative who carried a diagnosis of AAA.

Ultrasound study of the abdominal aorta after a 4-h fasting period was performed using a portable ultrasound scanner, Sonosite, M Turbo with a 5–2 MHz curved array transducer. B-mode gray-scale images of the aorta and iliac arteries were obtained in longitudinal and transverse orientations with the patient in the supine position. Measurements were obtained at the area of the largest inner diameter in the supra-celiac, supra-renal, and infra-renal aorta, as well as common iliac arteries. An infra-renal aortic diameter of 3.0 cm or larger was defined as an AAA. A common iliac diameter of 1.8 cm or larger was defined as an iliac aneurysm.

Duplex ultrasonography of the carotid arteries included grayscale, color flow, and Doppler studies of both common carotid and internal carotid arteries using a portable ultrasound scanner, Sonosite, M Turbo with a 10-5 MHz linear transducer. The normal result was defined as the absence of atherosclerotic plaque in the common and internal carotid arteries. In the presence of atherosclerotic plaque (thickness >2 mm), stenoses were divided into three categories according to the recorded peak systolic velocity (PSV): <50% (PSV < 125 cm/s), 50%–70% (PSV of 125–230 cm/s) and >70% (PSV >230 cm/s).

The Ankle-brachial index (ABI) was measured using a handheld continuous-wave Multi Duplex II bi-directional Doppler with an 8-MHz Doppler probe (Huntleigh Healthcare Ltd., Cardiff. UK) and standard 12 or 14 cm pressure cuff and an analog sphygmomanometer. Participants were asked to lie supine as flat as possible and keep the foot and leg still. Systolic brachial pressure (SBP) was measured bilaterally, and the highest pressure reading was recorded as a brachial pressure reference. Distal tibial systolic pressures were measured bilaterally, and the highest reading was used to calculate ABI using the standard formula (SPTP/SBP ratio) for each side. ABI ≤0.9 or >1.4 was considered abnormal.

All scans were performed by qualified (minimum of ultrasound or radiography degrees and Health Professions Council registered) and experienced (5–20 years of ultrasound experience) vascular ultrasonographers. All clinical teams followed identical protocols and were subject to a quality control program.[14]

For atrial fibrillation (AF), a standard 10-s limb-lead electrocardiogram (ECG) (leads iI, II, II, aVL, aVR, and aVF) were recorded on the screening day by applying four limb leads to both arms and both legs when participants were lying supine on a bed. Those with existing pacemaker or known, self-reported AF were excluded. ECGs were subsequently reviewed by a consultant cardiologist to indicate the presence or absence of AF. Limb-lead ECG was preferred to 12-lead ECG for ease, simplicity, and better privacy in the community settings, while also maintaining the ability to provide information for AF detection. When participants were diagnosed with AF, a copy of the ECG, along with their report, was posted to them advising participants to visit their GP for follow-up and appropriate course of action.

Statistical methods

Initially, the prevalence of AAA and IIA was determined for each 5 year age group for the whole population of 50,000 women studied. Subsequently, the mean (± standard deviation [SD]) of the AAA and IIA present were determined. The percentages of AAA with a maximum diameter ≥5.0 cm and IIA with a diameter ≥2.5 cm were also calculated.

Because the prevalence of AAA and IIA was very low in women younger than 66 and just over 1.0% in those over 85, subsequent analysis was confined to those in the age group 66–85 (n = 25,710) with 102 patients having AAA or IIA (prevalence of 0.40%). The association between potential risk factors and prevalence of AAA or IIA in this group was determined using univariate analysis and odds ratios.

After recording continuous variables that were not normally distributed [Table 1] the significant risk factors were included in a multivariable linear logistic regression analysis in three models with AAA or IIA as the dependent variable. Model 1 was based on history and comorbid conditions. Model 2 included the significant risk factors (independent predictors) from Model 1 with ABI and AF obtained from clinical examination and ECG. Model 3 included the presence of internal carotid stenosis (>50% in relation to the normal distal internal carotid) in addition to the significant risk factors in Model 2. After identification of the independent predictors for the presence of AAA or IIA, the predicted probability estimate for AAA or IIA was calculated for every individual in each model and used to construct ROC curves. The area under the ROC curve (AUC) was measured for each model.
Table 1: Prevalence of Isolated Iliac Aneurysms >1.8 cm and Abdominal aortic Aneurysms <3 cm in diameter in different age groups in 50,000 consecutive women screened with ultrasound

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Using a 0.5% probability for the presence of AAA or IA as a cutoff point, the number of women having an estimated probability >0.5% was determined. The actual prevalence of AAA or IIA was calculated in this group for each model.

All analyses were performed using IBM Corp. Released 2011. IBM SPSS Statistics for Windows, Version 20.0. Armonk, NY: IBM Corp.


  Results Top


A total of 116 women with an aneurysm were identified. Of these, 34 had an IIA in the absence of an AAA. IIA had a mean (± SD) maximum diameter of 2.35 ± 0.25 cm and range 1.9–2.8 cm. Of these, 12 (35%) had a maximum diameter of 2.5 cm or greater. The remaining 82 patients had an AAA with a mean (± SD) maximum diameter of 3.82 ± 0.85 cm and range 3.0–6.3 cm. Of these, 12 (14%) had a maximum diameter of 5.0 cm or greater.

The prevalence of AAA or IIA in different age groups of the 50,000 women screened is shown in [Table 2]. The results demonstrate that the presence of an aneurysm below the age of 66 years is rare. The prevalence increases with age from 0.27% in the 66–70 age group to 0.74% in the 81%–85% age group. The prevalence of AAA or IIA over the age of 85 is just over 1%.
Table 2: Association of risk factors with presence of abdominal aortic aneurysms or isolated Iliac aneurysms in 25,170 women aged 65-85

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In the age group of 66–85, there were 27,170 women with 102 (0.41%) AAA or IIA. The association between each risk factor and the prevalence of AAA or IIA is shown in [Table 1] using univariate analysis. Age, history of MI or CAD, history of stroke/TIA, hypertension, hyperlipidemia, history of smoking 10 pack-years or more, family history of AAA, presence of AF, ABI <0.9, and carotid bifurcation atherosclerosis were associated with increased prevalence of AAA or IIA. The strongest risk factor was the presence of internal carotid stenosis >50%, followed by smoking and ABI <0.9. Interestingly, diabetes and ABI >1.4 (data not shown), which is associated with incompressible arteries, were not associated with the presence of AAA or IIA.

The presence of any one of the risk factors listed in [Table 3] can identify a high-risk group with AAA IIA prevalence >1.0%, (range 1.18%–3.61%). In the age group of 66–85 consisting of 27,170 women, at least one of the first five risk factors listed was present in 3,170 women. This group contained 45 aneurysms (prevalence of 1.42%). When the family history of AAA is added to this list, then the presence of one of the first five risk factors and family history of AAA was present in 4419 women. This group contained 51 aneurysms (prevalence of 1.15%).
Table 3: List of risk factors that on their own can identify a high risk group with AA prevalence greater than 1.0% in 25,710 women age 66-85

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In a multivariable linear logistic regression analysis using the significant risk factors based on the history [Table 4], Model 1], age ≥76, hypertension, pack years ≥10, family history of AAA and history of stroke/TIA were independent predictors for the presence of AAA or IIA. Hyperlipidemia, family history of CAD, and family history of stroke or TIA were not significant. This model had an area under the ROC curve of 0.725 (95% confidence interval [CI] 0.673–0.777). For a probability >0.5%, this model could identify a high-risk group of 2947 women who had 41 aneurysms (prevalence 1.39%). By adding ABI and AF, which require a clinical examination and ECG [Table 4], Model 2], the prediction improved to an area under the ROC curve of 0.745 (95% CI 0.693–0.797). This model could identify 3693 women who had 51 aneurysms (prevalence 1.40%). Finally, by adding internal carotid artery stenosis greater than 50% [Table 4], Model 3], the predictive ability of the model improved even further with an area under the ROC curve of 0.775 (95% CI 0.724–0.826). This model could identify 3,701 women who had 58 aneurysms (prevalence 1.40%).
Table 4: Results of linear logistic regression

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  Discussion Top


This study shows that the prevalence of AAA or IIA in women increases with age stepwise [Table 2]. The prevalence is 0.27%–0.34% in the age group of 66–75 and 0.74–0.77 in the age group of 76–85. In ages over 65 a prevalence >1.0% is found in the presence of any of the following risk factors: history of MI (1.18%), history of stroke/TIA (1.21%), having smoked >10 pack-years (2.24%), ABI <0.90 (2.06%), carotid artery stenosis >50% (3.61%) and AF (2.17%). Thus, the presence of any of the above may become an indication to screen for AAA or IA. In addition, in this age group, 29% of the aneurysms detected were IIA. Including them in the screening protocol is justified because rupture is associated with a 50%–75% mortality.[11]

The higher prevalence of AAA in first degree relatives of females with AAA indicates that genetic susceptibility plays a key role in pathogenesis and is consistent with those of other studies.[15],[16],[17],[18] Smoking is a strong risk factor for AAA in both genders.[19],[20],[21],[22],[23],[24],[25],[26],[27] Our findings on hypertension and hyperlipidemia are consistent with previous publications, which reported that high blood pressure is an independent risk factor for AAA.[19],[20],[21],[22] Although elevated serum total cholesterol and low high density lipoprotein (HDL) cholesterol were shown to be associated with increased risk of developing an AAA by previous studies,[20],[28],[29],[30] they were not independent predictors for the presence of AAA/isolated IA in our series of 27,170 women.

AAA has historically been considered as a manifestation of atherosclerosis.[15] It has been shown that AAA and atherosclerosis share many risk factors such as age, smoking, hypertension, and hypercholesterolemia.[20],[21] Several studies have noted a higher prevalence of cardiovascular disease among AAA patients compared with subjects without an aneurysm.[9],[20],[22],[31] The findings of our study further support these reports and highlight the fact that women with a history of cardiovascular disease are more likely to develop AAA or IIA.

A limitation of this study is the potential of selection bias as only 1% of the invited population attended, and they may have done so because of family history or relatives with cardiovascular problems. However, the prevalence of major risk factors of this cohort is comparable with the published prevalence from population-based studies. In our population, aged 66–85 history if MI was present in 2.01%, which is similar to the 2.05% self-reported heart attack among females in a Canadian study.[32] and lower than the 3.5% coronary heart disease prevalence reported by the National Cardiovascular Intelligence Network.[33] The observed prevalence of hypercholesterolemia of 33% is also similar to that of US Heart Disease and Stroke Statistics published by the American Heart Association, showing an overall prevalence of 32% history of high cholesterol among women.[34] The prevalence of hypertension of 20% was lower than in population-based studies showing 28.5% prevalence among women in the last few years.[35] A history of stroke/TIA of 5.2% detected in our population is in line with WHO estimates on UK stroke prevalence among women (50/1000 population aged 65–74 and 79/1000 population in 75–84-year-old.[36]

One of the issues that emerge from our findings is that limiting AAA screening to men aged 65 and over is perhaps neglecting the needs of the female population and, therefore, a legitimate reason for reconsidering current recommendations. It should be noted that although women are inherently less likely to develop AAA or IIA than men, those who develop such aneurysms have a higher rate of rupture and higher mortality than men.[37] It is surprising that 29% of the aneurysms detected in our study involved the common iliac arteries without being associated with an AAA.

Conclusion

The findings of our study have important implications for developing a screening selection plan for women over 65. First, a search for IIA should be included in the screening protocol for AAA in women. Second, the presence of carotid stenosis ≥50% (symptomatic or asymptomatic) in women identifies a subgroup with a relatively high AAA or IIA prevalence of 3.6%. This finding suggests that any patient known to have such a lesion should have screening with ultrasound to exclude the presence of AAA or IA. The presence of any one or more of the other risk factors listed in [Table 3] can be used to develop targeted screening because of increased risk (>1%). However, whether such screening will be associated with benefits can only be determined by randomized controlled trials and cost-benefit studies. The authors hope that this paper, taken together with the initial report confined to AAA[14] will provide the stimulus for such studies.

Acknowledgments

The authors would like to thank all Ultrasonographers at Life Line Screening (LLS) for performing studies and LLS management, including but not limited to Dr. A. Manganaro, J. Waters, S. Zwicki, D. Jordan, J. Reizes, and J. Demchak, for providing us access to data. The study received funding from the Department of Surgery and Cancer, Imperial College, London.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.



 
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  [Table 1], [Table 2], [Table 3], [Table 4]



 

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