EPics I Study: Evaluation of Possible Abdominal Aortic Aneurysms (in Patients who have undergone Previous CABG)

Introduction

The validity, cost effectiveness and benefits of screening for abdominal aortic aneurysms (AAAs) in population-based studies have been clearly established.^1–6 A number of large population-based, randomized screening trials have reported a 3.6–7.6% prevalence of AAAs in men with most being in the 4% range, and in women, a 1% prevalence has been reported.^7–13 While much of the data have been accumulated on the prevalence of AAAs in men and women in large population-based studies, little has been written about the prevalence of AAAs in the subset of the population undergoing coronary artery bypass graft surgery (CABG).

Recently, Monney et al studied the prevalence of unsuspected AAAs in a group of male patients, 60 years of age and older, who were to undergo coronary artery bypass surgery.¹⁴ In 395 consecutive CABG patients, they found 40 unsuspected AAAs for a prevalence of 10.1%. This not only represents a significant increase in the prevalence of AAAs in men when compared to the prevalence reported in population-based studies, it also identifies a subset of patients who are at an increased risk of the lethal consequences of undiagnosed and untreated AAAs.

Purpose

Since little data beyond that reported by Monney et al exist on the prevalence of AAAs in the subset of patients undergoing CABG, our study sought to gather additional data on the prevalence of AAAs in both male and female patients, 60 years of age and older, who had undergone CABG to see if both groups are at a higher risk of developing AAAs than the population at large and thus might merit routine screening. Since no data exist on the prevalence of AAAs in females undergoing CABG, we felt it important to evaluate them to see if the prevalence of AAAs in this group was greater than the 1–1.3% prevalence reported in several of the large female population-based studies.

Methods

Permission for the study was obtained from the McLaren Regional Medical Center IRB. Eligible patients, males and females 60-years-old and older with a history of CABG, were self-enrolled after being notified of the study by their cardiac surgeon or when they learned of the study from advertisements. Eligible subjects were invited to enroll even if they had a history of having a known AAA being followed by their physicians, or if they had an AAA surgically treated. In this manner, accurate data on the prevalence of AAAs in CABG patients could be obtained. The AAAs identified strictly by screening and unknown to the patients were classified as “unknown” while those AAAs either being currently followed or previously treated were classified as “known”. In this manner, we could determine the importance of screening in the detection of AAAs in this group. Screening was performed by registered vascular technologists in our ICAVL approved vascular lab using a 6.2 MHz probe on HP, GE, Phillips or Siemens duplex machines. The criteria for the diagnosis of an AAA was an infra-renal aortic diameter of 30 mm or greater with the probe perpendicular to the axis of the aorta, the criteria used in many of the reported screenings and by the American Vascular Association.¹⁵ Data were also collected on the subject’s smoking history and the presence or absence of diabetes and hypertension. The study was initiated in September 2004 and completed in July 2005.

Results

The 772 patients, 525 males and 247 females, 60 years of age and older, who had undergone CABG were self-enrolled. Of the 525 men, 8 could not be screened because of obesity, resulting in a study group of 517 males. In this group, 47 AAAs were found for a overall prevalence of 9.0%. Sixteen of the 47 AAAs were either being followed by a physician or had been surgically treated (5 open repairs and 2 endovascular repairs), and were thus classified as “known” to the subjects, while 31 AAAs were discovered by the screening process and thus classified as “unknown”. Of the 247 females, 12 could not be screened because of obesity, leaving a study group of 235 females. In this group, 12 AAAs were found, for an overall prevalence of 5.1%. Six of the 12 AAAs were either being followed by a physician or had been surgically treated (2 open repairs, no endovascular repairs) and were classified as “known” to the subjects, and 6 were discovered by the the screening process and classified as unknown. 

In males, 30 of the 47 AAAs were in the 3.0–3.9 cm size, 11 of the 47 AAAs were in the 4.0–4.9 cm size, while 6 of the 47 AAAs were 5.0 cm and greater. In females, 6 of the 12 AAAs were in the 3.0–3.9 cm size, 4 of the 12 AAAs were in the 4.0–4.9 cm size and 2 of the 12 AAAs were 5.0 cm and larger. The predominant ethnic group was Caucasian (481 of the 517 males were Caucasian and 217 of the 235 females). In males, 46 of the 47 AAAs were found in Caucasians and 1 AAA was found in an African American. Similarly in the female study group, 11 of the 12 AAAs were found in Caucasians and 1 was found in an African American subject. For males in the 60–64 year age bracket, 100 males were screened and 7 AAAs were found, for a prevalence of 7%. In the 65–69 year age bracket, 111 males were screened and 6 AAAs were found (5.4%). In the 70–74 year age bracket, 131 males were screened and 13 AAAs were found (9.9%). In the 75–79 year age bracket, 95 males were screened and 10 AAAs were found for a prevalence of 10.5%, while in the 80-year and older bracket, 80 males were screened and 11 AAAs were found (prevalence 13.7%). For females aged 60–64, 57 were screened and 2 AAAs were found (prevalence 3.5%). For those aged 65–69 years, 53 females were screened and 3 AAAs found (5.6%). In the 70–74 age bracket, 48 females were screened and 2 AAAs were found (prevalence 4.1%). In the 75–79 age bracket, 48 females were screened and 3 AAAs were found (prevalence of 6.2%), while in the 80-year and older bracket, 40 females were screened and 2 AAAs found (5%). 

For males, 126 of 517 subjects never smoked, and in this group, only 3 AAAs were found (prevalence of 2.3%). Of the 517 males, 348 were former smokers and in this group 36 AAAs were found (prevalence of 10.3%). Also, 43 of the 517 males were current smokers, and in this group 8 AAAs were found, for a prevalence of 18.6%. In the females, 118 of the 235 subjects never smoked and 2 AAAs were found in this group (prevalence 1.6%). Of 235 female subjects, 101 were former smokers and in this group 7 AAAs were found (prevalence of 6.9%). Three AAAs were found among the 16 females who were current smokers (prevalence 18.7%). No history of diabetes was found in 335 of 517 males studied, and in this group, 39 AAAs were found (prevalence of 11.6%). Of the 171 males with a history of diabetes type I, 8 AAAs were found (prevalence of 4.6%). Eleven men had a history of diabetes type I, with no AAAs found in this group. In the female group, 141 of the 235 subjects had no history of diabetes (8 AAAs/prevalence 5.7%). A history of diabetes type II was found in 88 females, and in this group 4 AAAs were found (prevalence of 4.5%). Six females gave a history of diabetes type I and no AAAs were found in this group.

In males, 371 of 517 subjects were hypertensive, and in this group 36 AAAs were found, for a prevalence of 9.7%. One hundred forty-six of the 517 males were normotensive, and in this group 11 AAAs were found (prevalence 7.5%). In females, 198 of 235 were hypertensive and 11 AAAs were found (prevalence of 5.5%), while in the nonhypertensive group, 37 of 237, only 1 AAA was found (2.7%).

Discussion

This study was undertaken to evaluate the prevalence of AAAs in male and female subjects, 60 years of age and older, who had undergone coronary artery bypass graft surgery. There are many population-based studies screening the abdominal aorta to determine the prevalence of AAAs, mostly done in men, which are difficult to compare because the age at enrollment or the criteria used to determine the presence of an AAA differ. In spite of this, many AAA screening studies report a 4% prevalence in men and a 1% prevalence in women.^4–13 Overall, we found 47 AAAs in 517 male subjects who had undergone CABG, a prevalence of 9.0%, which is similar to the 10% reported by Monney et al in his study of the prevalence of AAAs in men about to undergo CABG.¹⁴ In 235 women with CABG, we found 12 AAAs, for a prevalence of 5.1%. The prevalence of AAAs in both male and female subjects with CABG was considerably higher than the prevalence of 4% for men and 1% for women reported in population-based studies and suggests that the subset of males and females undergoing CABG are at an increased risk of harboring an AAA and need to be screened prior to surgery.

In addition to this, more data should be collected on female subjects who have undergone CABG to see if the 5.1% prevalence of AAAs in this group persists. The prevalence reported here is considerably higher than the 1% reported for women in general, and would suggest that women about to undergo CABG should be routinely screened for AAA. To underscore the importance of screening in detecting AAAs in CABG subjects, it should be noted that only 16 of the 47 AAAs in men were known to the subjects before study enrollment and that 31 AAAs, 66% of the 47 AAAs discovered, were detected by the screening process. Similarly in women, only 6 of the 12 AAAs were known to the subject prior to the study, and the other 6 (50%) were detected by the screening process. This indicates that screening for AAAs in CABG subjects is very important.

Our findings are consistent with other studies which report that increasing age and smoking are independent risk factors for the development of an AAA.^7,16–20 With increasing age, the prevalence of AAAs increased in both male and female subjects. Similarly, smoking had been reported to be the single most preventable risk factor for AAAs. As reported in multiple studies, current smokers are 7.6 times more likely to have an AAA than non-smokers and ex-smokers are 3.0 times more likely to have an AAA than non smokers.^17–20 Our findings in men concur with these findings. Indeed, 44 of the 47 AAAs found in 517 male subjects were found in current or former smokers, whereas only 3 AAAs were found in the 126 men who never smoked, a prevalence of only 2.3%, lower than the 4% prevalence of AAAs found in population-based studies done on males. Of 43 males who were current smokers, 8 AAAs were found, for a prevalence of 18.6%. Similar results were found in women where 118 nonsmokers were found to have 2 AAAs, for a prevalence of 1.6%, the same as population-based studies on women; however 10 of the 12 AAAs found in women were in the group of former and current smokers. Three AAAs were found in 16 women who were current smokers, for a prevalence of 18.7%.

Our findings did not suggest a relationship between the presence of diabetes and AAAs. In men, only 8 AAAs were found in 171 diabetic type II subjects for a prevalence of 4.6%, while no AAAs were found in 11 diabetic type I subjects. Most of the AAAs found in men were in non-diabetic subjects. In 335 non-diabetics, 39 AAAs were found, for a prevalence of 11.6%.

Hypertension did not significantly impact the prevalence of AAAs in men. Thirty-six AAAs were found in 371 hypertensive males for a prevalence of 9.7% and 11 AAAs were found in 146 non-hypertensive men for a prevalence of 7.5%. In females, the prevalence of AAAs was higher in the hypertensive group where 11 AAAs were found in 198 hypertensive women and only 1 AAA was found in 37 non hypertensive subjects, suggesting that it may play a role in this group.

Our findings suggest that those undergoing CABG are at a higher risk of harboring an AAA and that this subset of the population merits routine screening of the abdominal aorta for AAAs prior to CABG surgery to determine the presence of an AAA. In addition, our findings suggest that the SAAAVE screening benefit provided by Medicare for new subscribers should be amended to provide screening of the abdominal aorta for women who have undergone or are about to undergo CABG.²¹

Conclusions

Male and females who have undergone CABG have a higher prevalence of AAAs than the population at large. In males with CABG, the prevalence of AAAs is 9% versus 4% for the general population, while in women with CABG the prevalence of AAAs is 5.1% versus 1% for the general population. Male gender, age and smoking are independent risk factors for AAAs, but diabetes and hypertension do not significantly impact the prevalence of AAAs. Screening was very important to the detection of AAAs in our male and female subjects. Sixty-six percent (31 of 47 AAAs) in men and 50% (6 of 12 AAAs) in women were found only through the screening process. With the documented importance of screening for the detection of AAAs in CABG, and with the increased prevalence of AAAs found in CABG subjects, screening for AAAs should routinely be done prior to CABG for both men and women. Furthermore, women who have undergone or are about to undergo CABG and are eligible for Medicare should be included in the AAA screening benefit of the SAAAVE legislation.