Abdominal aortic aneurysm screening

Associate Editors-In-Chief: Caitlin J. Harrigan [mailto:charrigan@perfuse.org], Amjad Almahameed MD, MPH.

Overview

 * Patients with abdominal aortic aneurysms (AAAs) are often asymptomatic, with the first clinical event often being fatal or life-threatening.
 * Due to this apparent "detection gap," pasternak between the asymptomatic disease and clinically apparent disease has increased the interest in screening in the medical community, and both in the general public and industry as well.
 * Screening for AAAs remains controversial because it fails to take lead time, length time, and overdiagnosis biases into account. Also, screening may be harmful if it leads to patients needlessly undergoing dangerous invasive procedures.

Why Screen for AAAs?

 * AAAs are defined as an aortic diameter of 3-6 cm, and are common in older people (10th leading cause of death in American men older than 65 years).
 * The same number of AAAs are still seen in emergency departments, despite advances in surgical techniques and in critical care practices heller
 * AAAs are usually asymptomatic during the latent stage, with the possibility of as many as one in three rupturing if left untreatable
 * A ruptured AAA carries an overall mortality rate approaching 75%, with a mortality rate of 2-6% in those patients who underwent elective surgical repair
 * Approximately 16% of large AAAs (diameter >5.5 cm)rupture, causing 9000 AAA-related deaths in the United States per year gillum
 * Several studies have shown that screening can drastically reduce the aneurysm rupture rate by 45-49% for men older than 60, and reduce AAA-related mortality by 21-68%.

The Multicenter Aneurysm Screening Study (MASS)

 * In the largest population-based screening study to date, the Multicenter Aneurysm Screening Study (MASS) randomized 67800 men (age 65-74) equally to either a group that received an ultrasound screening for AAA or a control group. ashton mass
 * In the screening group, men with an abdominal aorta larger than 3 cm in diameter were followed with serial ultrasounds for a mean duration of 4.1 years.
 * When the aneurysm reached 5.5 cm, grew more than 1 cm/year or became symptomatic, it was repaired surgically.
 * The aneurysm-related mortality was 53% lower in the screening group.
 * However, despite the relative risk reduction in the MASS trial, there were 65 AAA-related deaths in the intervention group (absolute risk of 0.19%), and 113 AAA-related deaths in the control group (absolute risk 0.33%).

Defining High-Risk Groups

 * Risk factors for aortic wall dilatation:
 * Male sex
 * Older age
 * Family history of AAAs or death from a ruptured aneurysm
 * Current or past smoking
 * Hypertension
 * Known atherosclerotic disease
 * Hypercholesterolemia
 * Cardiovascular risk factors tend to cluster in certain patients
 * Men who have hypertension, smoke and have other cardiovascular risk factors have an incidence of AAAs 2-5 times than those of the general population
 * Similarly, women over the age of 60 with cardiovascular risk factors are 2-3 times more likely to develop aneurysmal disease
 * Both diabetes mellitus and black race appear to be associated with a lower incidence of AAAs

Cost-Effectiveness of Screening

 * In a cost-effectiveness study in the United States, found a ratio of an AAA screening program to be $11,285 kent
 * This figure is comparable to the cost of such successful screening programs such as mammography for brest cancer detection, as well as therapeutic interventions (such as coronary artery bypass surgery).

Safety

 * The cornerstone of AAA screening is ultrasonography. It is available in almost every medical center and many physician offices.
 * Abdominal aortic ultrasonography is fast, inexpensive, safe and well-tolerated by most patients
 * It is highly accurate with 95% sensitivity and 100% specificity for AAAs laroy
 * The most important limitations of ultrasonography are:
 * Operator dependence
 * Reduced accuracy in those patients with bowel gas, periaortic disease and those patients who are obese
 * These limitations present less of an issue for highly experienced sonographers, and in accredited, validated, high-volume institutions
 * Clinical abdominal examination should be considered part of AAA screening and surveillance
 * Physical examinations may detect large AAAs, but is not specific or sensitive enough to detect smaller ones.
 * Computed tomography (CT) and magnetic resonance angiography are accurate for diagnosing AAA, but are less often used as a first-degree screening modality because of the lack of availability, and the risks and side-effects of iodinated contrasts for CT.

Ethics

 * Screening using ultrasonography causes no serious side effects, and is therefore ethically acceptable and accepted by patients
 * Several studies have shown that screening for AAAs and diagnosing asymptomatic small aneurysms in clinical practice were not associated with long-term emotional or psychological stress to patients vammen
 * A simple screening ultrasound test costs approximately $500, for which Medicare usually reimburses $160
 * Lack of insurance coverage raises the ethical delimma of AAA screening being available only to the elite who can afford it

Treatment

 * The purpose of screening is to enable patients with a disease to start therapy to change its course and prevent its complications
 * Other conditions that may affect the disease should also be addressed to omprove the overall health of patients and their short-term and long-term outcomes
 * The main treatment for AAA is surgical or endovascular repair
 * At this point, there have been no medications proven to affect aneurysm growth, and none is recommended for routine use
 * Current guidelines and expert consensus statements recommend repair of AAAs 5.5 cm in diameter or larger and of smaller AAAs that are rapidly expanding or that cause symptoms
 * There have been rapid advances in endovascular aneurysm repair in the United States, therefore stimulating a trend towards repairing smaller AAAs
 * However, the results of randomized controlled trials sugges it might not be beneficial
 * Endovascular repair may be a good option for sicker patients who are not candidates for open surgery
 * Further screening options would need to be expanded for those patients who do not qualify for open repair
 * Small, asymptomatic AAAs (3-5.5 cm) may serve as a marker for vascular disease elsewhere, thus finding one provides good reason to aggressively start to modify risk factors
 * AAA and atherosclerosis share many risk factors that tend to cluster
 * AAA patients have a high prevalence of systemic atherosclerosis:
 * 23-86% have coronary artery disease
 * 3-20% have cerebrovascular disease
 * 12-42% have peripheral arterial disease
 * Overall cardiovascular health is likely to be improved by lifestyle changes and medications for hypertension and dyslipidemia to achieve targets recommended for secondary prevention
 * Patients who quit smoking may stave off reaching the AAA repair size during their lifetime

Follow-Up Intervals

 * Periodic ultrasonographic surveillance is recommended for aneurysms smaller than the repair cutoff
 * However, definite and unified parameters for appropriate surveillance intervals have not yet been determined because clinical trials have enrolled heterogeneous populations and used different standards for diagnosis and management
 * In general, older men may need more frequent follow-up scans, as men older than 70 years have three times the rate of progression than younger men
 * Aneurysm diameters determined by ultrasound may vary up to 0.5 cm, which should be considered when recommending optial times for rescanning and repair

Acknowledgements
The content on this page was first contributed by: C. Michael Gibson M.S., M.D.