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Endovascular Aneurysm Repair in Challenging Anatomy
137
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In: Aortic Aneurysms ISBN: 978-1-62618-458-9
Editors: Daniel Fischhof and Franz Hatig © 2013 Nova Science Publishers, Inc.
Chapter 6
ABDOMINAL AORTIC ANEURYSM SCREENING
Kevin C. Chun
1
, Jacqulyne H. Sylvia
1
, Kai Y. Teng
1
,
Kiana M. Samadzadeh
1
and Eugene S. Lee
1,2
*
1
Department of Surgery, Sacramento VA Medical Center, Mather, CA, US
2
University of California, Davis, Sacramento, CA, US
ABSTRACT
Abdominal aortic aneurysm (AAA) ruptures cause 16,000 deaths a year.
Randomized clinical trials on AAA screening in Europe demonstrated ultrasonography
significantly reduces AAA-related mortality. As a result, AAA screening programs were
developed to prevent AAA ruptures by identifying and treating patients with AAA. An
AAA is defined as an aortic diameter about 1.5 times greater than a normal aortic
, the diagnosis of
AAA is made in 4-8% of males 65-75 years of age. Much research has been invested into
determining the causes of AAA development and expansion, so that screening yield of
patients and management protocols for patients with AAA can be improved. This chapter
discusses the screening parameters for the diagnosis of AAA, the evolution of AAA
screening from the randomized screening trials to current AAA screening programs, as
well as new research improving AAA screening yield and diagnosis.
I. INTRODUCTION
Abdominal aortic aneurysm (AAA) ruptures attribute a mortality rate of 85% [1] and
cause 16,000 deaths a year in the United States [2]. Randomized clinical trials on AAA
screening demonstrated ultrasonography significantly reduces AAA-related mortality. As a
result, AAA screening programs were developed to prevent AAA ruptures by improving early
diagnosis. An AAA is defined as a widening of the aorta, which is a diameter of about 1.5
*
Corresponding author: Eugene S. Lee, MD, PhD, 4860 Y Street, Suite 3400 Sacramento, CA 95817,
Eugenes.lee@ucdmc.ucdavis.edu Phone: 916-843-7202.
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Kevin C. Chun, Jacqulyne H. Sylvia, Kai Y. Teng et al.
140
current screening data, the incidence of AAA is usually around 4-8% of males 65-75 years of
age [4]. Much research has been invested into determining the causes of AAA development
and expansion. This includes identifying unique risk factors associated with AAA disease, as
well as observing the pharmacological effects on aortic expansion, to improve the screening
yield and diagnosis of AAA. This chapter discusses the diagnosis of AAA, the evolution of
AAA screening from the randomized trials to current AAA screening programs, as well as
new research into improving AAA screening yield and diagnosis.
II. DIAGNOSIS OF AAA USING IMAGING STUDIES
The diagnosis for AAA requires diagnostic imaging of the abdomen. This can be
accomplished either by ultrasonography, computed tomography (CT scan), or magnetic
resonance imaging. Any abdominal scan that detects an aneurysm must be verified by a
radiologist or a vascular specialist for AAA diagnosis. An AAA is defined as a widening of
the abdominal aorta, yet there is no clear consensus on the definition of AAA [3]. However,
an aortic diameter of at least 3.0 cm is the widely accepted clinical definition for AAA, and
aneurysm repair (EVAR)
[3-5].
Ultrasonography has become the front runner in detecting an AAA because it is a
noninvasive, inexpensive, and simple procedure to perform. Particularly, ultrasound
specificity and sensitivity for AAA are around 99% [6]. A four minute ultrasound has been
found more effective in measuring the abdominal aorta than CT scans and intraoperative
measurements [7]. Additionally, eliminating CT scans saves patients around $1600 a year in
health care costs [8]. Thus, many AAA screening programs utilize ultrasonography as the
primary method to detect AAA in patients.
Table 1. Summary of screening data from randomized trials
MASS
(2002)
Western
Australia
(2004)
Viborg
(2005)
Chichester
(1995)
Age range
65-74 years
65-83 years
64-73 years
65-80 years
Gender screened
Male
Male
Male
Male/Female
Total subjects in study
67,770
41,000
12,639
15,775
Total subjects screened
27,147/33,8
39 (80%)
12,203/17,516
(70%)
4843/6339 (76%)
5394/7887
(68%)
AAA detected in
screening
1333/27,147
(4.9%)
875/12,203
(7.2%)
191/4843(3.9%)
218/5394
(4%)
AAA-related mortality
reduced with screening?
Yes
No
Yes
Yes
Reported AAA surgeries
Elective Repair
322/1,333
(24.2%)
107/875
(12.2%)
48/191 (25.1%)
28/218
(12.8%)
Emergent Repair
80/1,333
(6%)
33/875 (3.8%)
5/191 (2.7%)
3/218 (1.4%)
AAA, Abdominal aortic aneurysm; MASS, United Kingdom Multicentre Aneurysm Screening Study
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Abdominal Aortic Aneurysm Screening
141
Figure 1. Ultrasound of a detected normal aorta. Crosshairs indicate location of aorta in the image with
a diameter measurement of 1.96 cm.
III. THE RANDOMIZED AAA SCREENING
STUDIES – EVALUATING AAA SCREENING
Evaluation of ultrasound screening for AAA has been examined primarily in four
randomized population-based studies. These four trials include the United Kingdom
Multicentre Aneurysm Screening Study (MASS) in 2002 [1], the Chichester trial in 1995 [9],
the Viborg County of Denmark trial in 2005 [10], and the Western Australia trial in 2004
[11].
A. The European and Australian Randomized Studies
The MASS trial (2002) [1] was a landmark study that produced the most comprehensive
data on evaluating AAA screening of a population to date. Approximately 68,000 randomized
subjects, males 65-74 years of age participated in the study. About half of the subjects were
chosen for screening and the other half were not screened. The results of the study indicate an
aneurysm detection rate of 4.9% of all patients screened for AAA [1]. Over the course of a 4-
year follow-up on participating subjects, screened subjects had significantly lower AAA-
related mortality than control subjects. Additionally, the number of AAA ruptures was also
significantly lower in screened subjects versus control subjects. Concurrently, a rise in the
number of elective AAA repairs and a decrease in emergent AAA repairs in screened subjects
were also reported [1]. The authors concluded that population-based AAA screening benefits
the older male population and significantly reduces AAA-related mortality.
The Chichester randomized trial (1995) [9] was considered to be the pilot study to the
much larger MASS trial. The study evaluated 16,000 men and women that were 65-80 years
of age. There were around 5,400 patients screened, with an AAA detection rate of 4% of all
screened subjects. Men themselves had around a 7.6% AAA detection rate. A 5-year analysis
of this study revealed a 42% decrease in AAA-related deaths in patients screened compared to
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Kevin C. Chun, Jacqulyne H. Sylvia, Kai Y. Teng et al.
142
patients not screened [9]. The trial concluded that AAA screening significantly reduced
AAA-related mortality and that screening women for AAA may not be needed.
The Viborg County of Denmark randomized trial (2005) [10] had over 12,000 male
subjects participate in the AAA screening program. The study revealed a 67% reduction in
AAA-related mortalities in screened men aged 64-73 years of age versus men that were not
screened [9]. An analysis determining AAA screening benefit also showed that 352 men
needed to be screened to save 1 life from AAA rupture [10]. The authors of this study further
speculated that running a population-based AAA screening program would be cost-effective
in the long-term because the number of emergent AAA repairs and AAA-related mortality
would decrease.
Figure 2. Ultrasound of a detected aneruysm. Crosshairs indicate location of the aneurysm in the image
with a diameter measurement of 6.52 cm.
Table 2. Summary of inclusion criteria for screening among active national AAA
screening programs
Medicare
(SAAAVE Act)
VA
NHS
Highland
Sweden
Age range
65 -75 years
65 -75 years
years
65 -74
years
years
Gender
screened
Male and Female
Male and Female
Male
Male
Male
Smoking
history?
Yes
Yes
No
Yes
No
Family
history of
aneurysms?
Yes, but only for
females
Yes, but only for
females
No
No
No
New to
health care
system?
Yes
No
No
No
No
AAA, Abdominal aortic aneurysm; SAAAVE, Screen for Abdominal Aortic Aneurysms Very Efficiently;
VA, Department of Veterans Affairs; NHS, National Health Service of England
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Abdominal Aortic Aneurysm Screening
143
The Western Australia trial (2004) [11] had the largest inclusive age group of all of the
randomized studies. There were 41,000 men, aged 65-83 years of age, which participated in
the study. The trial overall had an AAA detection rate of 7.6% of all patients screened.
However, compared to the other randomized trials, there was no observed significant decrease
in AAA-related mortality [11]. The study mentions that less than 1% of all subjects died from
AAA-related causes. However, a subgroup analysis of men between the ages of 65-74,
showed AAA screening significantly reduced AAA-related mortality, which produced similar
data from the other European randomized trials [11]. The authors of the Western Australia
trial concluded that designing a population-based AAA screening program should have a
specific targeted group within the age range of 65-74 years of age to increase the
effectiveness of the screening program.
IV. ESTABLISHING AAA SCREENING CRITERIA
An analysis of the randomized controlled studies was conducted by the United States
Preventive Services Task Force (USPSTF) [12] and a Cochrane review [13]. As a result, the
USPSTF recommended that men between the ages of 65-75 receive a one-time
ultrasonography screening for AAA if they smoked at least 100 cigarettes. Conversely, the
USPSTF recommends against screening non-smoking men between 65-75 and women [12].
The only exception USPSTF makes for screening women is if there is a clear family history
of aneurysmal disease.
Some vascular surgeons believe that the age range for AAA screening should be broader,
such as having all males aged 60-85 years of age, women aged 60-85 years of age with
prevalent cardiovascular risk factors, and anyone over 50 years of age with family history of
aneurysmal disease [14]. However, all of the randomized controlled trials found the subgroup
of males with an age range of 65-74 years to benefit the most from screening, even though the
trials primarily consisted of males 64-83 years of age [6]. Out of the 4 randomized controlled
trials, the MASS trial is widely considered the landmark study on AAA screening because it
was the largest and most comprehensively studied long-term of the randomized trials. The
USPSTF highly regards the MASS trial as a model of other AAA screening programs to
follow [12]. Thus, many AAA screening programs compare their results to the MASS trial to
determine their overall effectiveness.
V. AAA SCREENING IN THE UNITED STATES
AAA screening programs have also been established in the United States. There are no
current randomized clinical trials evaluating AAA screening in the United States. However,
there were several sponsored AAA screening trials. The Stroke and Aneurysm Vascular
Evaluation (SAVE) program [15] offered volunteers diagnostic screening for vascular
diseases, which included AAA screening. This study detected AAA in 2.1% of participating
subjects. The Dare to CARE trial [16] was a program to increase vascular disease awareness
in patients of the Annapolis, Maryland region. This study found AAA in 1.6% of their
subjects. Both the SAVE and Dare to CARE programs were primarily used to screen for
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Kevin C. Chun, Jacqulyne H. Sylvia, Kai Y. Teng et al.
144
vascular diseases and raise health awareness for the older population. The Aneurysm
Detection and Management (ADAM) study, led by the Veterans Affairs Cooperative Study
Group, screened 73,000 veteran patients 50-79 years of age [17]. The ADAM study detected
AAA in 1.4% of the total patients enrolled. The incidence of AAA detected in these
American screening programs is much lower than the randomized controlled trials.
Table 3. Summary of known risk factors associated with AAA diagnosis
Risk Factor
Association
Older Age
Positive
Male Gender
Positive
Smoking
Positive
Hypertension
Positive
CAD
Positive
Atherosclerosis
Positive
PVD
Positive
COPD
Positive
Elastin & Collagen Breakdown
Positive
Diabetes
Negative
AAA, Abdominal aortic aneurysm; CAD, Coronary artery disease; PVD, Peripheral vascular disease;
COPD, Chronic obstructive pulmonary disease
Figure 3. This diagram summarizes a standard protocol in identifying patients with an abdominal aortic
aneurysm in a screening program.
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Abdominal Aortic Aneurysm Screening
145
A. The SAAAVE Act
The Screen for Abdominal Aortic Aneurysms Very Efficiently (SAAAVE) Act was
implemented by the United States Federal Government in January 2007 in response to the
conclusions made by the USPSTF and Cochrane review [12, 13]. The SAAAVE Act was
designed to assist health care professionals in determining if their Medicare patients were at
risk of AAA by doing abdominal ultrasound screening. However, the SAAAVE Act only
applies to patients that are new to Medicare. This stipulation caused low rates of participating
subjects because physicians had to selectively choose Medicare patients that were deemed
eligible for screening. A more recent analysis on the impact of the SAAAVE Act revealed
only modest increases in AAA screening ultrasounds among Medicare beneficiaries, with no
impact to current elective or emergent AAA repair rates [18].
Due to the futility of the SAAAVE Act, Bill H.R 1213 was introduced in 2009 to modify
the SAAAVE Act [19]. This revision would remove the need for a physical examination prior
to screening to encourage additional Medicare patients to participate in AAA screening. This
proposed solution would increase the screening yield and the effectiveness of Medicare-
sponsored AAA screening programs across the United States. As of December 2012, the
revised bill has yet to become law.
B. AAA Screening and the Department of Veterans Affairs
The Department of Veterans Affairs (VA) initiated a more inclusive AAA screening
program mandated by the SAAAVE Act. The VA allowed any person that met USPSTF
guidelines to be eligible for AAA screening. This would increase screening yield more
significantly than the strict Medicare guidelines. Additionally, the VA Inspector General
reported AAA screening programs should be implemented at all VA medical centers because
the availability of staff and resources allows a national screening program to be feasible [20].
The VA Northern California Health Care System (VANCHCS) has an active AAA
screening program since January 2007 [21]. A 5-year analysis of the VANCHCS AAA
screening program [22] revealed an AAA detection rate of about 7.1% of all veteran patients
screened. This percentage of AAA detected was closer to the European trials than other U.S.
screening programs. Yet, there were some differences in the distribution of AAA detected.
The VA study found more 3.0-4.4 cm aneurysms versus the MASS trial, which may be
attributed to the high cardiovascular risk profile found in veterans compared to those of
similar age of the general population [23]. Furthermore, 28.2% of all patients screened in the
VA study were inappropriately screened because clinicians did not follow USPSTF
guidelines when referring patients for AAA screening. This study provided evidence that
some clinicians are unaware of USPSTF guidelines for AAA screening. The ordering of
unnecessary diagnostic studies for patients suspected with AAA amount to increasing health
care costs and provider burdens.
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VI. OTHER AAA SCREENING PROGRAMS
Other AAA screening programs exist throughout Europe and North America. The
Highland and Western Isles of Scotland AAA Screening Programme [24] was implemented in
2001 and found an AAA detection rate of 5.1%. Additionally, an analysis of the AAA
screening program determined there is a link between aortic diameter and poor health
outcomes in men screened for AAA. In England, the National Health Service (NHS) AAA
Screening Programme [25, 26] is the largest known AAA screening program implemented for
the general population. The NHS wanted to include as many eligible participants to be
included in the program. Thus, any male 65 years of age or older is eligible for AAA
screening. The NHS AAA screening program is expected to be fully deployed by 2013.
Sweden was the first country to institute nationwide coverage for AAA screening [27].
Over 90% of men 65 years of age or older are participating in a screening program within the
21 counties of Sweden. Moreover, Swedish AAA screening programs have attendance rates
of around 85%. Much of the high participation rates are attributed to each county using a
centralized hospital to coordinate AAA screening and inviting eligible subjects from a
national registry. Conversely, despite the success of screening programs, there is evidence
illustrating that Swedish AAA screening programs may need to alter AAA screening criteria
because of a growing population of elderly people and a constant rate of elective AAA repairs
[28].
In Canada, a national AAA screening program does not exist within the Canadian Health
Care System. However, vascular surgeons have urged primary care physicians to follow
certain guidelines when screening patients for AAA. Additionally, there is growing support
from the Canadian medical community for a national screening program. Based upon a
review of USPFTF and randomized trial data, both the Canadian Society of Vascular
Surgeons [29] and the Ontario Health Technology Advisory Committee [30] recommend a
national AAA screening program in Canada.
VII. LONG-TERM ANALYSIS OF AAA SCREENING
There is substantial evidence demonstrating long-term benefits from implementing AAA
screening programs to both patients and health care systems. Most of the long-term analysis
data came from the 10-year follow-up of patients enrolled in the MASS trial [31] and a 15-
year follow-up of patients from the Chichester trial [32]. Both long-term analysis studies
conclude that AAA screening still reduces AAA-related mortality.
The clinical benefits of long-term AAA screening are apparent. Screened patients with an
AAA tend to live relatively long life spans of about 11 years [32]. In the MASS trial, every
10,000 patients screened saved 75 patients from a ruptured AAA over 13 years. Specifically,
this meant approximately 216 patients had to be screened to save 1 person from AAA rupture
[31]. Additionally, 47 fewer AAA-related deaths were found in the screened group compared
to the control group [33]. The 10-year analysis on the Chichester trial showed a relative risk
reduction for AAA-related mortality in screened patients was 42% after 5 years and 21% after
10 years [32].
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