Screening for abdominal aortic aneurysms during transthoracic echocardiography

Screening for abdominal aortic aneurysms during transthoracic echocardiography M a r k J. Eisenberg, MD, MPH, S a l v a t o r e J. Geraci, RDMS, and Nelson B. Schiller, MD

San Francisco, Calif. Patients undergoing transthoracic echocardiography often have atherosclerotic vascular disease and may be at risk for the development of abdominal aortic aneurysms. We therefore examined the abdominal aorta by ultrasound in 323 consecutive patients undergoing routine two-dimensional transthoracic echocardiography over a 6-month period. Measurements were made of aortic length (diaphragm to most caudal portion visualized) and maximum diameter. The study group comprised 169 men and 154 women with an average age of 57 + 19 years (range 13 to 94). The abdominal aorta was imaged in 265 (82%) patients. The average aortic length visualized was 13.0 ± 4.6 cm, the average diameter 1.7 ± 0.4 cm, and the time required for screening <5 minutes. Seven (3%) patients were identified as having abdominal aortas ->2.5 cm in diameter: 1 with an aneurysm measuring 6.7 cm in diameter and 6 with mild dilatations measuring 2.5 to 3.0 cm in diameter. One of the patients with mild aortic dilatation was subsequently found to have an infrarenal aneurysm measuring 3.5 cm in diameter. Aortic dilatation was associated with male gender (p = 0.0006) and older age (p = 0.05) but was not associated with a history of ischemic heart disease (p = 0.16). From these results, we conclude that screening for abdominal aortic aneurysms in patients undergoing transthoracic echocardiography is practical and clinically useful. Only a small number of these patients are identified as having aneurysms, but the low cost and brief time required suggest that routine screening in this population may be worthwhile. (AM HEART J 1995;130:109-15.)

R u p t u r e of a b d o m i n a l aortic a n e u r y s m s is the thirt e e n t h most c o m m o n cause of d e a t h in t h e U n i t e d S t a t e s I a n d accounts for 1.2% of d e a t h s in m e n >65 y e a r s old. 2 More t h a n a t h i r d of p a t i e n t s w i t h acute aortic r u p t u r e die before r e a c h i n g the hospital; for those who do r e a c h the hospital, t h e operative morFromthe CardiovascularResearchInstitute,the CardiologyDivisionofthe Department of Medicine, and the John Henry Mills Echocardiography Laboratoryof the Universityof California,San Francisco. Dr. Eisenbergwas supportedbyan InstitutionalNationalResearchService Award,HL 07192,'~aining Programin Heart and VascularDiseases,National Heart, Lung,and BloodInstitute, Bethesda,Maryland. Receivedfor publicationJuly 25, 1994;acceptedDec. 12, 1994. Reprint requests:MarkJ. Eisenberg,MD, John HenryMillsEchocardiography Laboratory,Moffitt-LongHospital/Box0214, Universityof California, 505 Parnassus Ave.,San Francisco,CA 94143. Copyright© 1995by Mosby-YearBook,Inc. 0002-8703/95/$3.00+ 0 411163794

tality r a t e often exceeds 5 0 % . 3' 4 In c o n t r a s t w i t h e m e r g e n t s u r g e r y for r u p t u r e d a n e u r y s m s , elective s u r g e r y for a b d o m i n a l aortic a n e u r y s m s is associated w i t h a n in-hospital m o r t a l i t y r a t e of <5%, and long-term outcome in these p a t i e n t s approaches t h a t of p a t i e n t s w i t h o u t a n e u r y s m s . 5 T h u s optimal mana g e m e n t for patients with abdominal aortic aneur y s m s involves early identification and elective repair. 6-9 Because e a r l y identification of a b d o m i n a l aortic a n e u r y s m s is crucial, the utility of various screening strategies has been explored. I°, 11 T h e s e screening strategies include r e g u l a r physical e x a m i n a t i o n of the a b d o m e n and routine radiologic examinations. Although physical e x a m i n a t i o n is inexpensive, it has proved to be a n i n a c c u r a t e m e t h o d of detecting a n e u r y s m s a n d quantifying t h e i r severity. 12-14 In contrast, radiologic techniques can a c c u r a t e l y detect a n e u r y s m s and q u a n t i f y t h e i r severity, b u t t h e i r cost is high. 3' 10,15,16 Of the radiologic t e c h n i q u e s used for screening, a b d o m i n a l u l t r a s o u n d is the p r e f e r r e d m e t h o d because of its accuracy, ease, low cost, a n d noninvasive n a t u r e . Although not commonly appreciated, the equipm e n t used for t r a n s t h o r a c i c echocardiography is the same as t h a t used for abdominal u l t r a s o u n d examinations. Recently, d u r i n g one of our t r a n s t h o r a c i c echocardiographic studies, we incidentally discovered an abdominal aortic a n e u r y s m (see case r e p o r t t h a t follows). After this case, we decided to screen p a t i e n t s who were u n d e r g o i n g t r a n s t h o r a c i c echoc a r d i o g r a p h y for abdominal aortic a n e u r y s m s . Because m a n y of the p a t i e n t s r e f e r r e d for t r a n s t h o r a c i c echocardiography h a v e atherosclerotic v a s c u l a r disease, we hypothesized t h a t this p a t i e n t population m a y constitute a high-risk group for abdominal aortic a n e u r y s m s . Consequently, we prospectively exa m i n e d the abdominal a o r t a in 323 consecutive patients who u n d e r w e n t t r a n s t h o r a c i c echocardiograp h y over a 6-month period. O u r purpose was to d e t e r m i n e the practicality a n d clinical v a l u e of screening for a b d o m i n a l aortic a n e u r y s m s d u r i n g t r a n s t h o r a c i c echocardiography. 109

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Fig. 1. Abdominal aorta imaged with transthoracic echocardiographic equipment. Electronic calipers are used to measure length and maximum diameter of abdominal aorta.

An e x e m p l a r y case is a 75-year-old m a n w h o w a s a d m i t t e d to t h e h o s p i t a l w i t h u n s t a b l e a n g i n a in t h e s e t t i n g of a t r i a l fibrillation w i t h a r a p i d v e n t r i c u l a r r e s p o n s e . H e h a d a h i s t o r y of c e r e b r o v a s c u l a r disease, p e r i p h e r a l v a s c u l a r disease, a n d c o r o n a r y art e r y disease. T h e p a t i e n t h a d p r e v i o u s l y u n d e r g o n e b i l a t e r a l carotid e n d a r t e r e c t o m i e s , c o r o n a r y a r t e r y b y p a s s g r a f t s u r g e r y , a n d lefL v e n t r i c u l a r a n e u r y s m e c t o m y . H e w a s n e v e r n o t e d to h a v e a n a b d o m i n a l aortic a n e u r y s m , a n d t h e r e w a s no f a m i l y h i s t o r y of a n e u r y s m s . O n p h y s i c a l e x a m i n a t i o n , blood press u r e w a s 160/100 m m H g a n d h e a r t r a t e w a s irregu l a r a t a p p r o x i m a t e l y 120 b e a t s / m i n . L u n g s w e r e clear, cardiac e x a m i n a t i o n r e v e a l e d n o t h i n g r e m a r k able, a n d on e x a m i n a t i o n t h e a b d o m e n w a s r e p o r t e d as '%enign w i t h o u t p a l p a b l e o r g a n o m e g a l y . " After t h e p a t i e n t w a s a d m i t t e d to t h e cardiac care unit, a portable transthoracic echocardiographic study was p e r f o r m e d . While e x a m i n i n g t h e inferior v e n a c a v a f r o m t h e subcostal position, t h e s o n o g r a p h e r n o t e d t h e p r e s e n c e of a n a b d o m i n a l aortic a n e u r y s m m e a s u r i n g 5.3 c m in d i a m e t e r . After t h e p a t i e n t w a s disc h a r g e d f r o m t h e hospital, a n a b d o m i n a l u l t r a s o u n d e x a m i n a t i o n c o n f i r m e d t h e existence of t h e a n e u r y s m , a n d t h e p a t i e n t w a s s c h e d u l e d for elective repair. METHODS Patient population, The Moffitt-Long Hospital is a tertiary care medical center that serves as the main teaching hospital for the University of California at San Francisco. Over a 6-month period we prospectively examined 323

consecutive patients who were undergoing transthoracic echocardiographic studies with one of the sonographers at our institution. Patients were unselected and were referred for echocardiographic studies for a variety of reasons. Of the 323 patients examined, 163 (50%) were inpatients and 160 (50%) were outpatients. Eight (2%) patients had portable studies, and 315 (98%) had examinations performed in our echocardiography laboratory. Clinical information. Clinical information was obtained from the patient and the echocardiography requisition slip. The requisition slip was filled out by the physician requesting the echocardiographic examination and usually included a brief medical history and the reason the examination was requested. No medical history or reason for the echocardiographic examination was noted in <1% of the patients studied. Examination of the abdominal aorta. The abdominal aorta was examined from the subcostal position routinely used during echocardiographic examinations. 17 All examinations were performed by the same sonographer. More than 90% of the studies were performed with an Acuson (Mountain View, Calif.) 128 XP/10 with a 2.5 mHz transducer. The remainder of the studies were performed with a Sonos 1000 (I-Iewlett-Packard, Andover, Mass.) with a 2.5 mHz transducer. The equipment used to examine the abdominal aorta was the same as that used for the preceding echocardiographic examination. The abdominal aorta was identified as follows. The patient was placed in a supine position, and the transducer was positioned in the midline approximately 2 cm below the xyphoid (subcostal position). The transducer was then angled toward the patient's left until the aorta was identified as a pulsatile vascular structure. If the aorta was difficult to visualize, the patient was asked to bend the

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knees to relax the abdominal musculature. The aorta was readily distinguished from the inferior vena cava because the inferior vena cava is located to the right of the midline and its diameter usually varies with respiration. If there was any doubt as to which structure was the abdominal aorta, color Doppler was used to demonstrate blood flow away from the heart. Once the aorta was identified, it was examined in both the longitudinal and transverse planes. The length of the abdominal aorta that could be visualized was measured by using electronic calipers. One end of the calipers was placed at the point at which the aorta crossed the diaphragm, and the other end was placed at the point just prior to where the aorta was no longer visible (Fig. 1). The maximum diameter of the aorta was then determined by positioning the calipers just inside the inner layers of the aorta at the point that appeared widest by two-dimensional echocardiography. Dilatation of the abdominal aorta was considered to be present if its maximum diameter was ->2.5 cm. 14-1s Statistics. Continuous data are reported as mean _+ SD. Univariate and multivariate analyses were performed by using aortic diameter as a continuous dependent variable and age (->58 years or <58 years), sex, and history of ischemic heart disease as dichotomous independent variables. Unpaired Student's t tests were used for univariate analysis, and multiple linear regression was used for multivariate analysis. All hypothesis testing was two-sided, and a p value -<0.05 was considered to be statistically significant. RESULTS Patient population. O v e r a 6 - m o n t h period we pro-

spective]y e x a m i n e d t h e a b d o m i n a l a o r t a in 323 patients undergoing transthoracic echocardiography. T h e 169 (52%) m e n a n d 154 (48%) w o m e n h a d a n a v e r a g e age of 57 -+ 19 y e a r s (range 13 to 94). T h e d i a m e t e r of a t l e a s t t h e p r o x i m a l a b d o m i n a l a o r t a w a s i m a g e d in 265 (82%) p a t i e n t s . P a t i e n t s w e r e ref e r r e d for t r a n s t h o r a c i c e c h o c a r d i o g r a p h y for a varie t y of indications, a n u m b e r of w h i c h reflect t h e tert i a r y care n a t u r e of o u r h o s p i t a l (Table I). F o r e x a m ple, close to 20% of o u r p a t i e n t p o p u l a t i o n h a d e c h o c a r d i o g r a p h y in t h e s e t t i n g of p r o s t h e t i c v a l v e r e p l a c e m e n t , electrophysiologic studies, or o r g a n t r a n s p l a n t a t i o n . A m o n g t h e 265 p a t i e n t s w i t h ima g e a b l e aortic d i a m e t e r s , 19 (7%) h a d a h i s t o r y of ischemic h e a r t disease. Aortic dimensions and patients with aortic dilatation.

T h e a v e r a g e l e n g t h of t h e a b d o m i n a l a o r t a t h a t w a s v i s u a l i z e d w a s 13.0 + 4.6 c m (range 1.3 to 32.3 cm; Fig. 2), t h e m e a n d i a m e t e r w a s 1.7 _+ 0.4 c m (range 1.1 to 5.7 cm; (Fig. 3), a n d t h e t i m e r e q u i r e d to image t h e a b d o m i n a l a o r t a w a s <5 m i n u t e s . We identified 7 (2%) p a t i e n t s w i t h aortic d i a m e t e r s ->2.5 cm in width: 1 w i t h a n a n e u r y s m m e a s u r i n g 6.7 cm in

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Table I. Indications for transthoracic echocardiography in

323 consecutive patients screened for abdominal aortic aneurysms. No.

Assessment of left ventricular function* Valvular heart disease or heart m u r m u r Pre/post organ transplantationt Assessment of left ventricular function in setting of ischemic heart disease Assessment of prosthetic valves Pre/post electrophysiology study and/or bypass tract ablation Assessment of left atrial size in setting of atrial fibrillation Assessment ofleft ventricularwall thickness or mass Rule out mitral valve prolapse Rule out endocarditis Congenital heart disease Source of embolus Dyspnea Arrhythmia/palpitations Rule out pericardial effusion Chest pain Syncope Rule out thrombus Assessment of right ventricular function Pulmonary disease No indication noted on requisition TOTAL

%

93 36 26 21

29 11 8 7

20 18

6 6

16

5

15

5

13 12 11 9 6 6 4 3 3 3 3 3 2 323

4 4 3 3 2 2 1 1 1 1 1 1 <1 100

*Lei~ ventricular function was assessed for variety of reasons, including cardiomyopathy,pulmonary edema, prechemotherapy, and preoperative assessment. ~Organ transplantation included heart, lung, liver, kidney, and bone marrow.

d i a m e t e r (Fig. 4) a n d 6 w i t h mild dilatations m e a s u r i n g 2.5 to 3.0 c m in d i a m e t e r (Table II). A m o n g t h e 7 p a t i e n t s w i t h aortic dilatation, all w e r e i n p a t i e n t s , 6 w e r e m e n , a n d 6 w e r e ->50 y e a r s old (Table II). F o u r p a t i e n t s h a d a h i s t o r y of atherosclerotic v a s c u l a r disease, including one w h o h a d a previous resection of a thoracic aortic a n e u r y s m . Several p a t i e n t s h a d a b d o m i n a l i m a g i n g a f t e r b e i n g screened, a n d one of t h e s e p a t i e n t s w a s found to h a v e a n i n f r a r e n a l a n e u r y s m . This a n e u r y s m m e a s u r e d 3.5 cm in d i a m e t e r a n d e x t e n d e d to t h e r i g h t c o m m o n iliac artery. Univariate and multivariate analyses. Six (5%) of t h e 123 m e n h a d aortic dilatation c o m p a r e d w i t h 1 (< 1%) of t h e 141 w o m e n ; 5 (4%) of t h e 132 p a t i e n t s ->58 y e a r s old h a d aortic dilatation c o m p a r e d w i t h 2 (1.5%) of t h e 133 p a t i e n t s <58 a n d 1 (5%) of t h e 19 p a t i e n t s w i t h ischemic h e a r t disease h a d aortic dilat a t i o n c o m p a r e d w i t h 5 (2%) of t h e 244 p a t i e n t s w i t h o u t ischemic h e a r t disease. U n i v a r i a t e a n a l y s e s d e m o n s t r a t e d t h a t m a l e gender, older age, a n d a

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Fig. 2. Length of abdominal aorta that was visualized in 323 consecutive patients undergoing transthoracic echocardiography.

Fig. 3. Maximumdiameterofabd•minalaortain323consecutivepatientsundergoingtransth•racicechocardiography. history of ischemic heart disease were associated with aortic dilatation. Multivariate linear regression demonstrated t h a t aortic dilatation was associated with male gender (p = 0.0006) and older age (p = 0.05), but not with a history ofischemic heart disease (p = 0.16). DISCUSSION

Our study investigated the practicality and clinical value of screening for abdominal aortic aneurysms during routine transthoracic echocardiography. Over a 6-month period, we screened 323 patients. We identified 1 patient with a frank abdominal aortic aneurysm (6.7 cm in diameter) and 6 patients with mildly dilated abdominal aortas (2.5 to 3.0 cm in diameter). One of these 6 patients was subse-

quently found to have an infrarenal aneurysm measuring 3.5 cm in diameter. From these results, we conclude t h a t although only a small number of patients undergoing transthoracic echocardiography are identified as having abdominal aortic aneurysms, the ease and low cost of screening suggests t h a t it m a y be a worthwhile addition to routine transthoracic echocardiographic studies. Previous studies of screening strategies. Previous studies examined various screening strategies for the identification of abdominal aortic aneurysms. These studies found t h a t although physical examination is inexpensive, it is associated with a high rate of false-positive results, and it occasionally misses large aneurysms in obese patients. Collin et al. 14 examined 426 men aged 65 to 74 years and found t h a t

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Fig, 4. Abdominal aortic aneurysm detected during screening of 323 patients undergoing transthoracic echocardiography. Aneurysm measured 6.7 cm in diameter, and intraluminal thrombus is present.

the sensitivity of physical examination ranged from 35% to 44%, specificity from 91% to 97%, and positive predictive value from 22% to 36%. However, of the 23 patients found to have abdominal aortic aneurysms by ultrasonography, 15 had no suggestive findings on physical examination. This point is emphasized by the findings of Twomey et al., 19 who conducted a screening study in 200 men with hypertension and found that physical examination missed 5 of the 14 patients with abdominal aortic aneurysms, 1 of whom had an aneurysm measuring 8 cm in diameter. Thus, although physical examination may be an inexpensive screening technique for abdominal aortic aneurysms, it is associated with high rates of false-positive and false-negative results, and it not infrequently misses clinically significant aneurysms. In contrast with physical examination, abdominal ultrasound, computed tomography, and magnetic resonance imaging are highly accurate in detecting aneurysms and quantifying their severity. However, similar to physical examination, screening patients for abdominal aortic aneurysms with radio!ogic techniques is also problematic. Radiologic techniques are expensive, time consuming, and often have low yields. Because these tests are expensive, they are often only cost-effective for screening when they are used in high-risk populations. For this reason, many patients who are at moderate risk for abdominal aortic aneurysms m a y never be screened.

Screening during transthoracic echocardiography.

Screening for abdominal aortic aneurysms during transthoracic echocardiography has several advantages when compared with more traditional screening strategies. First, because the technique uses ultrasound, it is an accurate method for assessing the dimensions of the abdominal aorta. Second, the examination can be accomplished quickly and easily. The patient is already positioned, the ultrasound equipment is present, and the time required is brief. Third, because the equipment used to screen for abdominal aortic aneurysms is the same as that used for the preceding transthoracic echocardiography study, there is little or no cost associated with screening. Finally, many patients being screened are at increased risk for harboring abdominal aortic aneurysms. Many patients are older, and many have known atherosclerotic vascular disease. Because these patients are often at higher risk for abdominal aortic aneurysms than people in the general population, screening among patients undergoing transthoracic echocardiography may have a higher yield than screening in the general population. Implications of mild aortic dilatation. Six of the patients we screened had mild dilatation of their abdominal aortas, and 1 of these patients was subsequently found to have an infrarenal aneurysm. These findings have two important implications. First, the finding of a mildly dilated proximal ab-

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Table II. Patients identified as having abdominal aortic dilatation during transthoracic echocardiography

Aortic dimensions (cm) History

Reason for echocardiography

Age

Sex

80

F

Multiple myocardial infarctions, palpitations

Pre-electrophysiologic study

2.7

8.9

79

M

Assess left ventricular function

6.7

14.8

77

M

Hypertension, elevated cholesterol, previous coronary artery bypass surgery Prostate disease

2.8

--

71

M

Assess left ventricular function Post-electrophysiologic study

3.0

14.1

Alive at 9 mo

66

M

Assess left ventricular function

2.5

12.5

50

M

Assess left ventricular function

2.6

9.7

36

M

Assess left atrial size

2.7

7.0

Multiple abdominal CT and MRI scans without evidence of aneurysm; alive at 1 yr Multiple abdominal ultrasound examinations without evidence of aneurysm; alive a t i yr alive at 10 mo

Arrhythmias, recent electrophysiologic study, thoracic aortic aneurysm repair Bladder cancer

Intraoperative myocardial infarction during liver transplantation New-onset atrial fibrillation, morbid obesity, pickwickian syndrome, probable sleep apnea

Diameter

Length

Follow-up Abdominal CT scan revealed 3.5 × 3.5 cm infrarenal aneurysm extending to right common iliac artery; alive at 1 yr Refused surgery; alive at lyr

Lost to follow-up

CT, Computed tomography; MRI, magnetic resonance imaging.

dominal aorta may suggest the presence of a more distal aneurysm. Consequently, patients with mild dilatatioh of their proximal abdominal aortas should probably be referred for further imaging studies to look for more distal aortic aneurysms. Second, although patients with mild aortic dilatation are at low risk for rupture, they m a y be at risk of developing significant aortic dilatation in the future. A number of studies have examined the rate of aortic enlargement in patients with preexisting aortic dilatation. Several studies suggest t h a t the mean rate of aortic dilatation for aneurysms (6.0 cm in diameter approaches 0.5 cm/year. 2°' 21 In contrast, one population-based study demonstrated a median rate of enlargement of only 0.21 cm/year. 22 Nevertheless, the authors of t h a t study reported t h a t 24% of their patients had a rate of expansion ->0.4 cm/year. That study also confirms the findings of earlier studies, which showed t h a t smaller aneurysms enlarge at a

slower rate t h a n larger aneurysms. 23 Because patients with mild dilatation of abdominal aortas may be at risk of significant aneurysms in the future, it is probably prudent to perform a complete abdominal ultrasound examination in these patients and to repeat it at regular intervals to assess for a change in aortic diameter. 24, 25 Unless serious contraindications exist, patients with aneurysms ->5.0 cm in diameter should be scheduled for elective repair. Limitations. Two potential limitations of our study should be noted. First, the yield of aneurysms in our patient population was low; only 2 aneurysms were found in >300 patients examined. Thus, in spite of being a higher-risk group of patients t h a n the general population, the prevalence of aneurysms in patients undergoing transthoracic echocardiography was low. Several factors m a y account for our low yield. First, our echocardiography laboratory is located in a tertiary care medical center, and for this

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reason we may have a lower proportion of patients with atherosclerotic vascular disease than many other echocardiographic laboratories. Because a number of specialized procedures are performed at our institution (e.g., valvular surgery, accessory bypass tract ablation, organ transplantation; Table I), a smaller proportion of our patients may have vascular disease and abdominal aortic aneurysms compared with patients seen in other clinical settings. Consequently, aneurysm screening in community settings may have a greater yield than that found in our patient population. Second, women made up close to 50% of the patients we examined. Because women have a much lower incidence of abdominal aortic aneurysm than men, the yield of aneurysms in our study is not comparable to that of previous studies. Finally, close to half of our patients were <50 years of age. Because the incidence of abdominal aortic aneurysms rises markedly after the age of 50, the high prevalence of younger patients in our study may also be responsible for the low yield in our study. If we had restricted our study to men >50 years old, we would have identified 1 patient with an aneurysm and 4 patients with mild aortic dilatation among 74 patients, for an overall yield of 7%. A second possible limitation of our study is that we only examined an average of 13 cm of the proximal abdominal aorta. Abdominal aortic aneurysms are most often localized to the infrarenal aorta and the iliac arteries. Consequently, the brief examination performed during transthoracic echocardiography may not detect abdominal aortic aneurysms located in the distal abdominal aorta and iliac arteries. Thus, although aneurysms can be detected during transthoracic echocardiographic studies, this screening technique should not be used in place of a rigorous examination of the abdomen by an experienced abdominal ultrasound technician or by examination by more sophisticated radiologic techniques. Echocardiography technicians are not routinely trained in the examination of the abdominal aorta and should therefore not be relied on for the diagnosis of abdominal aortic aneurysms. If aortic dilatation is detected during echocardiography, the patient should be referred for a confirmatory radiologic examination. Conclusions. We examined whether screening for abdominal aortic aneurysms during transthoracic echocardiography is practical and clinically useful. We found that only a small number of patients undergoing transthoracic echocardiography are found to have abdominal aortic aneurysms but that the low cost and brief time required suggest that this exam-

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ination may be a worthwhile addition to routine transthoracic echocardiographic studies. REFERENCES

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