Abdominal Aortic Aneurysm

Abstract

Men are more likely than women to develop an abdominal aortic aneurysm (AAA), a disease that is often asymptomatic and has up to a 90% risk of mortality if the aneurysm ruptures. What many men do not know is that an AAA can easily be identified through an ultrasound screening, and if the aneurysm is >5.5 cm, it can be surgically repaired to prevent a life-threatening rupture. Although current AAA screening recommendations focus on men between the ages of 65 and 75 years, who have ever smoked, recent evidence suggest many men of ages 50 to 80 years, regardless of smoking status, may also be at risk for developing an AAA. This article presents a comprehensive overview of AAA disease and summarizes current evidence-based diagnostic and treatment guidelines, the importance of educating men about this health issue, and the need for more widespread AAA ultrasound screening opportunities.

The aorta is the largest artery in the body, carrying oxygenated blood from the heart and eventually to all parts of the body through systemic circulation. The diameter of the aorta as it passes through the abdominal cavity is approximately 2.0 cm. However, this abdominal portion of the aorta may become dilated, weakened, and place stress on the aorta wall. This condition is referred to as an abdominal aortic aneurysm (AAA), and there is up to a 90% risk of death if an AAA ruptures (Centers for Disease Control and Prevention, 2011).

It is well established that men, especially those more than the age of 65 years, are more likely than women to develop an AAA (Cosford, Leng, & Thomas, 2007). The exact prevalence of AAA disease in the United States is unknown, but extrapolating retrospective data from a cohort of 3.1 million patients aged 50 to 84 years who had been screened for an AAA, Kent et al. (2010) estimated the prevalence to be 1.1 million persons. This approximation reflects all AAA in the United States, of which 569,000 are estimated to be among women, nonsmokers, and individuals less than the age of 65 years.

Unfortunately, individuals who have an AAA may not experience any symptoms until the aneurysm ruptures and becomes life threatening. According to the Centers for Disease Control and Prevention (2011), there is up to a 90% risk of death if an AAA ruptures. It has been estimated that among individuals with an acute AAA rupture, approximately half (50%) die before reaching a hospital. Of those who do arrive at a hospital alive, approximately 50% will not survive emergency surgical repair of the rupture (Aggarwal, Qamar, Sharma, & Sharma, 2011).

The risk of an AAA rupturing increases with an increase in the size of the aneurysm. An AAA with a diameter >5.0 cm has an approximately 20% risk of rupture. If the diameter of an AAA is >6.0 cm, the risk of rupture increases to approximately 40%. The risk of rupture in an AAA with a diameter >7.0 cm is more than 50% (Centers for Disease Control and Prevention, 2011). To prevent rupture of AAA and the associated risk of death, the goal is to diagnose individuals who have an AAA, and if the diameter of the aneurysm is >5.5 cm, repair the aneurysm as an elective surgical procedure (Cosford et al., 2007).

Risk Factors

Risk factors associated with the development of an AAA include the following: a family history of an aortic aneurysm, a history of smoking, hypertension, hypercholesterolemia, and atherosclerosis (Centers for Disease Control and Prevention, 2011). Kent et al. (2010) also reported age, gender, lower extremity peripheral artery disease, carotid artery disease, history of a cerebrovascular event, being overweight or obese, and ethnicity (being Caucasian or Native American) as risk factors significantly associated with AAA disease.

Gender is considered a risk factor since men are six times more likely to develop an AAA when compared with women. Most studies comparing men and women with an AAA report similar risk factor profiles, but women with an AAA tend to be 3 to 5 years older than men at the time of presentation, and the presence of a history of cardiovascular disease tends to be the predominate predictor of AAA development in women (Cornuz, Pinto, Tevearai, & Egger, 2004). In a cohort study of 3.1 million people screened for an AAA, men accounted for 79.3% of all individuals found to have an AAA (Kent et al., 2010).

According to Norman and Powell (2007), one possible explanation for a lower incidence rate of AAA disease in women is the role of the sex hormone estrogen. Evidence suggests that endogenous estrogen may play a protective role against cardiovascular disease development in premenopausal women, and this protective mechanism against cardiovascular disease may also delay development of AAA in women. The use of hormone replacement therapy in postmenopausal women has not been shown to reduce the risk of coronary heart disease and is not thought to affect AAA development in postmenopausal women. Also, according to Norman and Powell, the aorta is biologically stiffer in men than in women, and this may be a contributing factor in the higher rates of AAA disease in men. Although the incidence of AAA disease is lower in women than in men, it is important to note that emerging evidence suggests women who develop an AAA may have a greater risk of AAA rupture (Lederle, 2008; Norman & Powell, 2007; Sweeting, Thompson, Brown, & Powell, 2012).

Smoking is another risk factor for developing an AAA in men and women. Historically, men have smoked more than women, but this trend has recently been reversed. Norman and Powell (2007) suggest that smoking may actually be a greater risk factor in women, and chronic hypertension may be a more significant risk factor in men. Kent et al. (2010) confirmed smoking as the major AAA environmental risk factor, and they reported that among smokers the risk of developing an AAA increased with duration of smoking and quantity of cigarettes smoked per day.

In men, Wanhainen et al. (2005) reported the dominant risk factors for developing an AAA were age (being more than 60 years of age), smoking, significant family history, chronic hypertension, and dyslipidemia. However, the researchers reported less significant correlations between cardiovascular disease and the development of an AAA if individuals were treated for chronic hypertension and dyslipidemia. It is important to note that although a significant correlation between diabetes, dyslipidemia, and the development of occlusive cardiovascular disease has been established, evidence shows that diabetes actually provides protection against AAA development and is not a risk factor for the disease (Lederle, 2012; Norman, Davis, Le, & Golledge, 2007).

Symptoms

Creating awareness about AAAs is important. In many cases, AAAs do not produce any signs or symptoms until the aneurysm ruptures. Often an AAA is discovered when an abdominal ultrasound or computerized tomography (CT) scan is ordered for the diagnosis and treatment of another condition. When an AAA does produce symptoms, the most common symptom is pain. According to Wedro, Lee, and Shiel (2012), this pain is characterized as being deep, usually occurring in the middle of the abdomen, and often radiating to the back. Pain associated with an AAA is usually constant, but may be relieved by changing position. An AAA that is rapidly expanding may cause sudden onset of severe, steady, and worsening pain in the middle abdomen and back. An AAA may produce a prominent pulsation that may be felt by palpating either side of the aorta in the midline of the abdomen. The presence of a pulsation is more difficult to detect in obese individuals. A person with an AAA that is near rupture may report tenderness on palpation. Auscultation with a stethoscope may also reveal a bruit or abnormal sound from turbulent blood flow within the aneurysm. If an AAA ruptures, there may be abdominal distension, a pulsating abdominal mass, and possible signs of shock secondary to massive blood loss.

Diagnostics

Researchers have reported the effectiveness of using abdominal ultrasounds in screening asymptomatic individuals for the presence of an AAA and reducing mortality from AAA ruptures (Cosford et al., 2007; Kent et al., 2010; Ogata et al., 2006). Unfortunately, ultrasound screening to detect the presence of an asymptomatic AAA is not covered by most insurance companies in the United States (Ogata et al., 2006). A one-time AAA ultrasound screening is covered under Medicare Part B during a participant’s first 12 months of enrollment in the plan. The participant must have a positive family history for an AAA, or be a male, ages 65 to 75 years, who has smoked at least 100 cigarettes in his lifetime. The referral for an AAA ultrasound screening must be made as a result of a participant’s “Welcome to Medicare” preventive visit (U.S. Department of Health and Human Services, n.d.).

Limited coverage of AAA ultrasound screenings by insurance companies and Medicare, as well as limited promotion of AAA ultrasound screenings in general, are due in part to restrictive AAA screening guidelines developed by the U.S. Preventive Services Task Force (USPSTF). In 2005, the USPSTF recommended that men aged 65 to 75 years who have ever smoked receive a one-time screening for an AAA. The USPSTF made no recommendations for or against AAA screening in men aged 65 to 75 years who have never smoked. There are no recommendations for AAA screenings in men less than the age of 65 years. Kent et al. (2010) estimated that only half of all individuals with an AAA are eligible for ultrasound screening under these current screening guidelines. The half who are not currently eligible include all women, men between the ages of 50 to 64 and 76 to 84 years who have ever smoked, and men aged 50 to 84 years who have never smoked. Kent et al. reported that in a cohort of 3.1 million, nonsmokers accounted for 19.8% of individuals found to have an AAA, and women accounted for 20.7%.

Because it is noninvasive and cost-effective, abdominal ultrasound is the preferred method of screening individuals for an asymptomatic AAA. However, according to Hunink and Gazelle (2003), an abdominal ultrasound is not as reliable or accurate as a CT scan. These authors suggest that for diagnostic purposes, the image provided by a CT scan is superior to images obtained through ultrasound. Magnetic resonance imaging (MRI) may be used as an AAA diagnostic procedure, but Hunink and Gazelle report MRI is not as reliable as a CT scan and is cost-prohibitive.

Treatment Options

Treatment options for an AAA include the following: observation via routine ultrasound surveillance, medical management, lifestyle changes, and either open or endovascular surgical repair. Treatment is based on whether the patient is symptomatic, the size of the aneurysm, and associated risk factors. The natural history of AAA progression, the risk of surgical treatment, and the life expectancy of the patient must all be considered when making treatment decisions. Greenhalgh and Powell (2008) recommend patients receive unbiased information about research findings, as well as advantages and disadvantages regarding treatment options.

Surveillance

The current “best practice” recommendation is to conduct routine ultrasound surveillance of an asymptomatic AAA <5.5 cm in diameter. Surgical repair is recommended if an AAA is symptomatic and/or >5.5 cm in diameter. Filardo, Powell, Martinez, and Ballard (2012) analyzed survival data of patients in four randomized controlled trials of individuals with an AAA of 4.0 to 5.5 cm in diameter, comparing outcomes of those who received immediate surgical repair with patients who received routine ultrasound monitoring. These trials included 3,314 patients with a mean follow-up of 10 years, and the researchers concluded that immediate repair of an AAA 4.0 to 5.5 cm in diameter showed no significant difference in long-term survival. No advantage to surgical repair was found until the aneurysm enlarged to >5.5 cm in diameter or the patient became symptomatic. It should be noted, however, that 31% to 75% of individuals randomized into one of the four surveillance groups eventually had AAA surgical repair. Also, since emerging evidence indicates women may have a greater risk of AAA rupture, Sweeting et al. (2012) suggested that women may benefit from surgical intervention before an AAA is 5.5 cm or greater in diameter.

Medical Management

In addition to routine ultrasound surveillance, medical management may be helpful in patients with a small-to-medium size AAA. Medical management includes the use of various pharmaceutical agents to minimize the expansion rate of an AAA. However, data supporting the use of most pharmaceutical agents in the management of an AAA are inconsistent. The use of statin therapy in the management of AAA growth rates is one such example. Statin medications are used to reduce total cholesterol concentrations, and a number of researchers have suggested statins may slow the expansion rate of AAAs (Van Kuijk et al., 2009). However, of the eight clinical studies, involving 4,466 AAA patients using statins that were reviewed by Dunne et al. (2012), only four studies demonstrated reduced AAA expansion. Because many patients with an AAA also have a concomitant diagnosis of dyslipidemia, Vega de Ceniga, Blanco-Colio, Tuñón, Egido, and Martin-Ventura (2012) recommended all AAA patients be treated with statins to reduce the incidence of cardiovascular events and death. Additionally, Paraskevas, Wierzbicki, and Mikhailidis (2012) reported that an association has linked statin usage with improved perioperative and long-term morbidity and mortality rates in all vascular patients.

Many individuals with an AAA also have hypertension, and if untreated, it may increase stress on arterial walls. Some researchers have suggested using beta-blockers in managing AAA progression, but data on the effectiveness of this therapy are also inconsistent. Assar (2009) reported that propranolol (a beta-blocker) did not significantly affect AAA expansion rate during two double-blind, randomized, controlled trials in patients with a small AAA; however, Aggarwal et al. (2011) recommend beta-blockers for nonsurgical AAA patients with comorbidities of hypertension or angina.

Biopsies of AAA tissues universally reveal signs of chronic inflammation (Norman et al., 2007), and it has been suggested that antibiotic therapy may be useful in AAA management by inhibiting inflammatory processes. The use of doxycycline has been shown to prevent AAA formation in animal models. In a small clinical trial evaluating the effect of short-term doxycycline therapy in preoperative AAA repair patients, researchers did report a reduction in aortic wall inflammation and neutrophil content (Abdul-Hussien et al., 2009). In addition, Chlamydia pneumoniae may play a role in AAA pathogenesis, further supporting the use of antibiotic therapy. However, the benefits of using antibiotics in AAA prevention and management are unclear, and additional research is needed (Aggarwal et al., 2011).

Lifestyle Changes

It has been estimated that >90% of patients diagnosed with an AAA are current or previous smokers, and evidence suggests that nicotine may play a role in AAA pathogenesis through elastin degradation (Assar, 2009). Kent et al. (2010) reported the risk of developing an AAA was higher for current smokers than those who had smoked in the past and quit. Assar (2009) reported that smoking cessation may be effective in decreasing the rate of AAA progression. Therefore, in individuals diagnosed with an AAA who are current smokers, a smoking cessation program is recommended as part of the treatment plan. Smoking cessation programs may include the use of pharmaceutical agents and/or behavior modification.

Kent et al. (2010) reported that in a cohort of 3.1 million individuals who had been screened for an AAA, two thirds were overweight or obese, having a body mass index > 25. Within this cohort, Kent et al. found a negative association between developing an AAA and certain “heart healthy” lifestyle behaviors. These included individuals who exercised at least once per week and those who consumed fruits, vegetables, and nuts more than three times per week. Considering these findings, and the widely reported association between AAA development and coronary artery disease, individuals diagnosed with an AAA may benefit from following a heart healthy diet and exercise regimen.

Surgical Repair

Surgical repair of an AAA may be accomplished through an open or endovascular procedure. Pearce, Zarins, and Bacharach (2008) reported that since the first successful open surgical repair of an AAA in 1951, improvements in surgical and anesthetic techniques have lowered death rates from 25% to <10%. The risk of cardiopulmonary, wound, and late graft complications after open surgical repair varies between 13% and 23%. Endovascular aneurysm repair (EVAR) is a less invasive surgical alternative for AAA patients. According to Pearce et al., benefits of EVAR included less blood loss, decreased intensive care, shorter hospital stays, more rapid recovery, and earlier return to function. However, negative factors associated with EVAR include increased rates of graft-related complications, re-interventions, and increased cost. Joels et al. (2009) reported that open AAA repair is the procedure of choice for patients with minimal comorbidities and an expected long-term survival of more than 5 years.

Paraskevas, Mikhailidis, and Veith (2011) reported the EVAR approach is associated with higher mortality rates with increasing age and lower mortality rates in abdominal aneurysms less than the standard threshold of 5.5 cm in diameter. In the EVAR 1 trial, 1,252 patients with an AAA >5.5 cm in diameter were randomized into two groups and underwent either endovascular or open repair. Brown et al. (2012) reported a lower operative mortality in the EVAR group; however, no differences were seen in total mortality or aneurysm-related mortality in the long term (8 years). Additionally, long-term outcome data regarding AAA size threshold, procedure cost, patient age, life expectancy, and patient comorbidities are needed to fully assess the merits of both procedures and assist individual decisions whether repair should be performed by open or endovascular surgical procedures.

Conclusions

Evidence supports that men are more likely than women to develop an AAA, and the risk of death from an AAA rupture can be reduced through early diagnosis, monitoring, and surgical repair of the aneurysm if it is >5.5 cm in diameter. Elective surgical repair of an AAA prior to rupture is the desired outcome, and saves lives. Since most individuals with an AAA have no symptoms, it is important to encourage those at risk to have an AAA ultrasound screening. Current AAA ultrasound screening guidelines are restrictive and limiting, recommending screening only for men aged 65 to 75 years who have a history of smoking. However, there is more recent evidence that many men between the ages of 50 and 80 may be at risk for developing an AAA, regardless of smoking history.

It has been estimated that 1.1 million individuals in the United States may have an AAA. The majority of these individuals are men, and most may not know they have an AAA. It is important to generate more awareness about AAA disease among all men, regardless of age and smoking status. Men need to be aware of the risk factors associated with developing an AAA to make informed decisions about lifestyle choices and preventative health measures as they age. Men who are at risk of developing an AAA should be encouraged to have an AAA ultrasound screening. As more and more men in the baby-boomer generation age, greater access to AAA ultrasound screening programs are needed.

The fact that nonmodifiable risk factors such as race, gender, age, and family history are associated with the development of an AAA, it may be impossible to completely prevent this potentially fatal disease. However, risks associated with AAA development and progression may be reduced by adopting heart healthy behaviors; this is another reason to encourage all men to adopt such a lifestyle. Modifiable factors such as smoking cessation, cardiovascular enhancing dietary and exercise practices, as well as compliance with medications to treat hypertension and dyslipidemia are all practices that may be beneficial in reducing the risk of AAA in men.