Cath Lab Digest

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 (Table 1). 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.

Table 2 categorizes the AAAs found in the male and female subjects by their greatest diameter, dividing them into three categories: 3.0–3.9 cm, 4.0–4.9 cm and 5.0 cm and greater. 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.