Screening for Abdominal Aortic Aneurysm During Transthoracic Echocardiography in a Hypertensive Patient Population

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1 Screening for Abdominal Aortic Aneurysm During Transthoracic Echocardiography in a Hypertensive Patient Population Peter C. Spittell, MD, Io-Ellen Ehrsam, RDCS, RVT, RDMS, Laurie Anderson, RDCS, and James B. Seward, MD, Rochester, Minnesota This study was undertaken to determine the utility of transthoracic echocardiography as a screening test for occult abdominal aortic aneurysm in hypertensive patients older than 50 years of age. Longitudinal and transverse images of the abdominal aorta were obtained during the subcostal portion of the transthoracic echocardiogram. Abdominal aortic aneurysm was defined as an abdominal aortic dimension (antero-posterior or lateral) >-3.0 cm. Exclusion criteria induded prior abdominal aortic aneurysm repair, known abdominal aortic aneurysm, or inadequate images of the abdominal aorta (nine patients). Two hundred patients (107 men, 93 women; mean age 71 years, range 51 to 92 years) met the study inclusion criteria. An occult abdominal aortic aneurysm was identified in 13 patients (6.5%). Sixty-nine percent of the abdominal aortic aneurysm patients were men, with a mean age of 73 years and a mean duration of hypertension of 11 years. Seventy- seven percent had a history of tobacco use, and 15% had a positive family history of abdominal aortic aneurysm. All aneurysms were infrarenal in location, with abdominal aortic aneurysm diameter ranging from 3.0 to 5.2 cm (mean 3.9 cm). Laminated thrombus was present in six patients (46%), and in one patient a right common iliac artery aneurysm was also detected. Imaging of the abdominal aorta during transthoracic echocardiography required an average of 6.7 minutes (range 4 to 10 minutes). In conclusion, the abdominal aorta could be accurately imaged in the majority of patients (96%) undergoing transthoracic echocardiography in this study. The incidence of occult abdominal aortic aneurysm in hypertensive patients older than 50 years of age is significant (6.5%). Screening for occult abdominal aortic aneurysm in this patient population should be a routine extension of the transthoracic echocardiogram. (J Am Soc Echocardiogr 1997;10:722-7.) Abdominal aortic aneurysm (AAA) is frequently asymptomatic and often occult on physical examination, and its incidence appears to be increasing. 1-4 Furthermore, the increased mortality rate from ruptured AAA 1,s-8 and the low risk of elective surgical resection 1,6,9d underscore the importance of early detection and repair. Numerous studies have shown the high sensitivity and specificity of ultrasound in the detection of AAA; nonetheless, ultrasound screening programs have not been found to be cost effective in a population screened solely for this condition. However, when population screening focuses on patients with one or more risk factors for AAA (male gender, advanced age, hypertension, family history of abdominal aortic aneurysm, peripheral or coronary arterial From the Echocardiography Laboratol T and Division of Cardio vascular Diseases and Internal Medicine, Mayo Clinic and Mayo Foundation. Reprint requests: Peter C. Spittell, MD, Division of Cardiovascular Diseases and Internal Medicine, Mayo Clinic, 200 First St. S.W., Rochester, MN Copyright 1997 by the American Society of Echocardiography /97 $ /1/ occlusive disease and/or cerebrovascular disease), the incidence of AAA increases significantly The purpose of this study was to investigate the utility of a modified abdominal aortic ultrasound examination, performed as an extension Of a transthoracic echocardiographic examination. Furthermore, can such an examination simply, safely, and accurately identi~ occult AAA in patients at increased risk? MATERIALS AND METHODS Between September 1995 and April 1996 a prospective study was undertaken which consisted of a limited ultra sound examination of the infi'arenal abdominal aorta in patients referred to our echocardiography laboratory for routine transthoracic echocardiography. Inclusion criteria for the study included age greater than 50 years and hypertension of greater than 1 year in duration. Patients with a known or suspected A,~A or prior AAA repair were excluded from the study. Echocardiographic evaluation of the abdominal aorta was performed with the use of an Acuson (model Nol 128XP10, Mountain View, Calif.) or Hewlett-Packard

2 Journal of the American Society.of Echocardiography Volume 10 Number 7 Spittell et al. 723 Figure 1 Diagram of the modified abdominal aortic ultrasound examination. The abdominal aorta is imaged in the longitudinal (long-axis) and transverse (short-axis) planes from the subcostal and abdominal transducer positions. (model No. Sonos 1000, 1500, or 2500) equipped with a 2.5 M H z echocardiographic transducer. Imaging of the abdominal aorta was performed in the supine position during the subcostal portion of the transthoracic echocardiogram. Images were acquired from the subcostal and abdominal transducer positions to visualize the abdominal aorta to the level of the aortic bifurcation (Figure 1). Two-dimensional imaging in the longitudinal and transverse planes was used to illustrate the area of greatest aortic diameter. Special attention was given to demonstrating the aortic bifurcation in the longitudinal and transverse planes to ensure that the infrarenal abdominal aorta was assessed during the examination (Figure 2). Measurements in the transverse (anteroposterior and lateral) and longitudinal (antero-posterior) planes were made using still frame images and "on-line" video calipers. Diameters were measured from leading edge to leading edge. All studies were performed by examiners with training in both transthoracic echocardiography and peripheral vascular ultrasound (P.C.S., I.E., L.A.). If an abnormality was found, the attending physician was notified and the findings were included in the echocardiographic report. The abdominal aortic examination was considered an extension of the transthoracic examination and not a separate formally reimbursable test. For the purpose of this study, an aneurysm was defined as a focal enlargement of the abdominal aorta of at least 3.0 cm in maximum anteroposterior or lateral dimension. ~S~TS T w o h u n d r e d nine patients w h o met age and hypertension criteria u n d e r w e n t ultrasound screening o f the abdominal aorta during transthoracic echocardiography. The reason for performing the echocardiogram was suspected or k n o w n cardiac disease. Examination o f the abdominal aorta was attempted in all study patients despite b o d y habitus, recent f o o d intake, or prior unrelated abdominal surgery. I n nine patients (4.3%), intestinal gas or obesity precluded adequate visualization o f the entire abdominal aorta and these patients were excluded from further study. Adequate images o f the abdominal aorta were obtained in 200 patients (95.7%), 107 m e n and 93 w o m e n, mean age 71.3 years (range 51 to 92 years). T h e average examination time required for evaluation o f the abdominal aorta was 7.7 minutes (range 1 to 20 minutes) (Table 1). Thirteen patients (6.5%) were f o u n d to have an occult infrarenal AAA. Nine o f the patients with AAA were m e n (69%). T h e mean age o f patients with AAA was 73.2 years (range 54 to 88 years). Hypertension was present an average o f 11.2 years. Systolic and diastolic b l o o d pressure in patients with AAA ranged from 104 to m m H g (mean 148 m m H g ) and 70 to 110 m m H g (mean 87 m m H g ), respectively. T e n

3 724 Spittell et al. Journalof the AmericanSocietyof Echocardiography September 1997 Figure 2 Modified two-dimensional ultrasound examination of the abdominal aorta showing a 3.7 cm infrarenal abdominal aortic aneurysm. A, Longitudinal view of abdominal aortic aneurysm (arr0w). B, Transverse views of the proximal abdominal aorta (arrow). C, Aneurysm with mild amount of laminated thrombus (arrow). D, Aortic bifurcation into proximal right and left common iliac arteries (arrowheads). D, Color flow Doppler imaging is used to show the aortic bifurcation.

4 Journal of the American Society of Echocardiography Volume 10 Number 7 Spittell et al. 725 Table 1 Clinical and demographic variables of the study population Total group (n = 200) AAA group (n = 13) Gender Men 107 (54%) 9 (69%) Women 93 (46%) 4 (31%) Age (yr) Mean Range Body surface area (m 2) Mean Range Duration of hypertension (y) Mean Range Tobacco No 117 (58%) 3 (23%) Current or prior use 83 (42%) 10 (77%) Family history of A_&& No 187 (93%) 11 (85%) Yes 13 (7%) 2 (15%) Abdominal aortic diameter* (cm) Mean Range Thrombus present* No 7 (54%) Yes 6 (46%) Examination time (rain)* Mean Range AAA, Abdominal aortic aneurysm. *Antero-postcfior abdominal aortic diameter in transverse plane. *In patients with abdominal aortic aneurysm. *Abdominal aorta examination time. patients (77%) had a current or prior smoking history. Two of the patients (15%) with AAA had a firstdegree relative with AAA. Aneurysm size ranged from 3.0 to 5.2 cm, with four patients (31%) having an aortic diameter exceeding 4.5 cm. Laminated thrombus was identified in six patients with AAA. In one patient in whom a 3.9 cm AAA was detected, an aneurysm involving the tight common iliac artery (1.7 cm) was also identified. DISCUSSION The incidence of occult AAA in the general population is estimated to be between 1% and 2%, an incidence too low to warrant widespread screening programs),2,~7 Fortunately, acknowledged risk factors for AAA allow identification of a "target population" in whom the incidence of AAA ranges from 2.7% to as high as 13.4%, depending on the risk factors used to select the population to be studied. H,18-24 Using age as the only risk factor, the incidence of AAA in persons between 68 and 80 years of age has been reported to be 2.7%. 18 When male gender, age greater than 55 years, and hypertension are used as selection parameters, the incidence of AAA increases to 13.4%. 20 Furthermore, ultrasound screening programs for AAA in persons with lower extremity arterial occlusive disease and/or cerebrovascular disease have shown an AAA incidence of 5.9% and 8.4%, respectively, ls,2a Therefore, screening programs for AAA should focus on "high-risk" patient populations to be clinically meaningful and cost effective. Abdominal palpation as a sole means of detecting AAA has limitations (reduced sensitivity and specificity) in patients with small ancurysms and in obese patients and requires considerable examiner experience. Physical examination alone, therefore, is not sensitive enough to be the sole screening test for AAA. Ultrasonography, on the other hand, is widely recognized as highly accurate in the diagnosis of AAA. The ability to acquire high quality images of the abdominal aorta and to detect AAA during TTE has previously been reported. 14,1s Eisenberg et al. t5 screened for AAA during TTE in 323 consecutive patients referred for echocardiography. No further selection parameters were used. The mean age of the patients was 57 years and the incidence of occult AAA was 3%. In a subsequent study by Schwartz et al., t4 250 consecutive patients referred for TTE (men over age 55 years and women over age 65 years), underwent screening for AAA. The overall incidence of AAA was 4.6% when patients with a known AAA were excluded from analysis. In the present study, in which the stated purpose was to evaluate a modified abdominal aortic ultrasound evaluation performed during TTE to detect occult AAA, the overall incidence of AAA was 6.5%. Using the selection parameters of age greater than 50 years and chronic hypertension (greater than 1 year in duration), the incidence of occult AAA was comparable with previous studies of "high-risk" pa-

5 Journal of the American Society of Echocardiography 726 Spittell et al. September 1997 tients, la,2,2s The clinical features most commonly present in hypertensive patients with AAA were age greater than 70 years, male gender, and a history of tobacco use. The absolute specificity of this method of screening for AAA cannot be statistically derived because all patients with normal or negative results did not undergo further testing (computerized tomography, magnetic resonance imaging). Despite this limitation, the rate of false-negative results is probably quite low given the demonstrated accuracy of ultrasonography. Even if the rate of false-negative results was significant, patients would be no worse off than before TTE because physical examination performed by the referring physician had also given negative results. It is noteworthy that, in the present study, adequate images of the abdominal aorta were obtained in greater than 95% of patients in spite of no special preparation. Inadequate images of the abdominal aorta during TTE have previously been reported to be as high as 14%? 4 When a modified abdominal aortic ultrasound examination is incorporated into the echocardiographic study, the requirements of additional time are modest, no additional equipment is required, and the potential benefits to the patient are substantial. For example, an AAA diameter of between 4.5 cm and 5.0 cm in patients with an acceptable surgical risk is currently a well-recognized indication for selective surgical repair. In our study, nearly one third of the patients with an occult AAA had an aneurysm size ->4.5 cm, a group likely to benefit from consideration for surgical therapy. Furthermore, given a predicted AAA expansion rate of 0.4 cm/year, 2s it would be expected that even the smallest AAA in our study group would attain a diameter approaching or exceeding 4.5 cm within 3 years of initial detection. In addition, identification of occult AAA at a smaller size (smaller than 4.5 cm) may allow institution of pharmacologic therapy (beta adrenergic blockade) to decrease the rate of aneurysm expansion 26 and improved treatment of associated hypertension, if present. Earlier detection of AAA at a smaller size and careful clinical follow-up may also result in a decrease in the mortality from ruptured AAA. CONCLUSION Although the overall prevalence of AAA is not increased in the general population, the prevalence of AAA is increased in patients with identifiable risk factors for AAA. AAA is often asymptomatic and may not be clinically apparent on physical examination. Ultrasonography is highly accurate in the diagnosis of AAA and screening for AAA can be readily incorporated into the TTE examination. Furthermore, the abdominal aorta can be accurately imaged in the majority of patients (96%) undergoing TTE. 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