Late survival risk factors for abdominal aortic aneurysm repair: Experience from fourteen Department of Veterans Affairs hospitals

Late survival risk factors for abdominal aortic aneurysm repair: Experience from fourteen Department of Veterans Affairs hospitals Joe Feinglass, PhD, Diane Cowper, MA, Dorothy Dunlop, PhD, Rael Slavensky, RN, MA, GaryJ. Martin, MD, and William H. Pearce, MD, Chicago, Ill. Background. This study evaluates late survival risk factors for patients who underwent elective abdominal aortic aneurysm surgical procedures performed at 14 Department of Veterans Affairs hospitals across the United States between 1985 and 1987. Methods. Preoperative risk factors for a representative sample of 280 male veterans were obtained from an extensive Department of Veterans Affairs Office of Quality Management study and subsequent chart review. The National Death Index was used to determine survival through December 1991. Results. Mortality at 30 days was 2. 9%. Kaplan-Meier survival probabilities were 89% (+-2%) at 1 year and 64 % (+-3%) at 5 years. Multivariate hazards models indicated significantly poorer survival for patients with age greater than 69 years, chronic obstructive pulmonary disease, cerebrovascular disease, and left ventricular hypertrophy. A history of coronary artery disease including previous myocardial infarction or bypass operation did not predict late survival for this cohort. Conclusions. Given the substantial burden of comorbidity of veterans who use Department of Veterans Affairs facilities, the overall survival experience of this all male cohort compares well with previously published series and with overall U.S. male life expectancy. The fact that a history of coronary artery disease did not predict survival for this cohort may be related to selection bias; however, a more likely explanation is the presence of unsuspected coronary disease among patients without a documented history of angina or myocardial infarction. (Stm6V~I" 1995;118:16-24.) From the Division of General Internal Medicine and Division of Vascular Surgery, Northwestern University Medical School; the Centerfor Health Services and Policy Research; Northwestern University; the VeteransAffairs Health ServicesResearch and Development Service Centerfor Health Services and Policy Research, Hines VeteransAffairs Hospita# and the Division of Vascular Surgery, VeteransAffairs Lakeside Medical Center, Chicago, Ill.

DESPITE DECLININGOPERATIVEmortality rates reported at

large centers, a significant risk of death and disability still accompanies elective abdominal aortic aneurysm (AAA) surgical procedures. Whereas published case series indicate that the recent operative mortality rate in larger centers is less than 4%, 1 population-based data present a somewhat less favorable picture. One nationally representative, all-payor sample of discharges from 664 U.S. hospitals for 1987 indicates a 7.2% hospital mortality rate for patients with a principal diagnosis of Supported by grant IIR 91-100.Afrom the Veterans AffairsHealth Services Research and DevelopmentService. Accepted for publication Dec. 21, 1994. Reprint requests: Joe Feinglass, PhD, Division of General Internal Medicine/NUMS, 303 E. Ohio, Suite 300, Chicago, IL 60611.

11/56/63054

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SURGERY

unruptured abdominal aortic aneurysm. 2 This finding is consistent with a New York state hospital study that f o u n d a 7.6% death rate for 3570 operations for unruptured AAA during the years 1985 through 1987. 2 Data from the Department of Veterans Affairs (DVA) Patient Treatment File for all DVA hospitals during fiscal years 1990 through 1993 indicate that there was an overall 5.2% hospital mortality rate for 5799 patients discharged after undergoing operation for unruptured AAA. Given the risks of operation for AAA, providing patients with realistic expectations about late survival after operation is a key element for obtaining truly informed consent for this procedure. Knowledge of late survival probabilities is becoming even more important as some clinicians urge ultrasonography screening pro, grams for high-risk populations. These programs are

Surgery Volume 118, Number 1 likely to find significant numbers of older patients with small aneurysms less than 5 cm in transverse diameter. 4-6 O n g o i n g clinical trials in the United States and Europe are now exploring the efficacy of surgical resection of smaller aneurysms. 7 However, decisions about surgical treatment of patients with AAA will continue to be related to late survival risk factors such as age and the presence of chronic disease. 8q~ With the advent of new treatment modalities such as endovascular stents, 11 the durability of surgical repair will also affect decisions about which patients are the best candidates for alternative treatment. This article analyzes the specific risk factors that influenced late survival for a cohort o f male veterans undergoing operation at 14 DVA medical centers during the mid-1980s. Veterans who use DVA facilities are at particularly high risk for aneurysmal disease; one study conducted at a DVA medical center found a 9% prevalence rate for AAA in male veterans who were 60 to 75 years of age and had hypertension or heart disease. 5 It was therefore of special interest to examine the survival experience of surgically treated patients with AAA across a broad spectrum of DVA medical centers throughout the United States.

PATIENTS, MATERIAL, AND METHODS The sample for this study was drawn from patients whose medical records were previously abstracted for the DVA Office of Quality Management's Retrospective Surgical Mortality and Morbidity Risk Modeling Study, which was completed in 1990. The original study, which was based on a representative sample of approximately 2500 patients treated at 14 DVA medical centers, focused exclusively on operative mortality and morbidity rates for six surgical procedures. An original 339 patient "aortic resection" sample was drawn from all discharges with a relevant principal procedure, including patients with ruptured aneurysms, discharged between fiscal years (FY) 1985 and 1987 from the two DVA medical centers with the highest surgical volumes in each of the (then) seven VA regions. Original study methods, which include medical record abstraction techniques for more than 150 data elements and have an interrater agreement rate of more than 95% for history and physical findings items, are reported in a multivolume final project report available from the DVA Office of Quality Management) 2 The original aortic resection sample in that study, consisting of 339 records, was reduced to 280 patients with aneurysmal disease for this study by selecting only those patients with an International Classification of Diseases-ninth revision-Clinical Modification primary diagnosis code for unruptured AAA (441.4) and a prin-

Feinglass et al.

17

T a b l e I. Patient frequencies by VA medical center Boston Ashville Buffalo Denver Hines Houston Long Beach Little Rock Memphis Milwaukee Minneapolis Nashville Richmond Wadsworth TOTAL

9 36 29 2 17 31 7 31 14 17 45 11 12 19 280

cipal procedure code for aortic graft replacement operation (38.44). A single female patient was deleted to obtain an all male sample. Medical records for each of the final 280 patients were retrieved from the investigators in the original study and were reabstracted for this study by two vascular surgery clinical nurse specialists. The distribution of procedures by DVA medical center is included as Table I. Risk factors measured at the time of operation included age, race, the presence of abdominal tenderness on physical examination, examination, the urgency of hospital admission, renal artery involvement, a history of smoking or alcohol use, and documentation o f 11 chronic disease comorbidities. (Cancer was not included because only two patients had documented carcinomas.) Patients with overt coronary artery disease were further analyzed by a history of myocardial infarction (from history or electrocardiography findings), myocardial infarction within 1 year of AAA operation, and previous coronary artery bypass operation. Finally, aneurysm size at operation was noted for 249 (88%) of the 280 patients on the basis of ultrasonography or computed tomography findings; for the remaining 31 patients medical records documentation of aneurysm size was too poor to be considered reliable. The Goldman Cardiac Risk Index (CRI score), originally designed as a predictor score for the likelihood of cardiac complications in noncardiac surgical procedures, is was also calculated for all patients on the basis of relevant history and physical and laboratory findings. The American Society of Anesthetists Anesthesia Physical Status Classification 14 was determined and documented at the time o f operation for 266 (95%) patients. These composite measures were designed to measure operative risk for general surgical procedures, and

18

Feinglass et al.

although they have been found to be somewhat less specific (80% to 85%) as predictors of cardiovascular complications for patients with AAA, 15~16 the scores nevertheless represent clinically important risk stratifications. It was therefore of interest to determine how well these easily obtained composite measures predicted late survival. Survival of all patients through December 1991 was verified by use of the National Death Index (NDI), a service of the National Center for Health Statistics. All decedents were matched to state death certificate data by first and last names, social security number, birth date, gender, race, and, in most instances, state of death. NDI date of death data were checked against all deaths noted in patients' medical records and longitudinal DVA Patient Treatment File computer searches, which were found to correspond exactly to NDI data. Univariate survival analysis was performed for each potential baseline risk factor with the product limit estimator of Kaplan-Meier to construct survival curves for the strata. The log rank test was used to determine whether the stratified survival curves were significantly different. A nominal value o f p < 0.05 from the univariate analysis was used to determine which candidate risk variables (other than the composite risk ratings CRI class and Anesthesia Physical Status Classification score) were tested in a multivariate survival model. The proportionality assumption of the Cox proportional hazards model was checked by plotting hazard function curves for each candidate risk factor found to be significant in the univariate analyses. When hazard plots of-log(-log S) versus time were not equidistant, results from a multivariate Weibul regression model, which does not require the proportional hazards assumption, 17 were compared with the Cox model results. RESULTS

The 280 patients who underwent operation had a mean age of65.9years (SD = 7.0). Eight (2.9%) patients died within 30 days of hospital admission. A total of 113 (40.4%) patients had died before December 1991, the last m o n t h of NDI follow-up. Table II presents 1-year and 5-year Kaplan-Meier cumulative survival probabilities by risk factor for all patients in the sample. Overall 1-year survival was 89.2% -+ 1.8%, and overall 5-year survival was 64.2%-+ 2.9%. Cumulative survival was 50% -+ 5% at just u n d e r 7 years. Risk factors with significantly lower survival included age greater than 69 years (p = 0.008), a history of kidney disease (on the basis of abnormal preoperative creatinine level p = 0.02), cerebrovascular disease (including

Surgery July 1995 history of either stroke or transient ischemic attack, p = 0.02), cardiac arrythmia (p = 0.04), chronic obstructive pulmonary disease (p = 0.02), and CRI index classification greater than level one (p = 0.007). Although a history of hypertension was not a significant predictor of survival, a finding of left ventricular hypertrophy on preoperative electrocardiography was predictive of significandy reduced survival (p = 0.007). Evidence of congestive heart failure was at the borderline of statistical significance (p = 0.06) and was therefore also tested in the multivariate survival model. Of interest was that symptomatic coronary artery disease (including a history of angina) was not a significant predictor of survival. Separate tests of patient subgroups with a history of myocardial infarction, previous coronary bypass graft operation, and pathologic Q waves on preoperative electrocardiogram were also nonsignificant. Only 12 patients had myocardial infarctions within 1 year of their AAA operation, and this group's survival experienc e was also not significantly different. Only four discrete risk factors were found to be significant at p < 0.05 in the multivariate regression model. These were age greater than 69 years, chronic obstructive pulmonary disease, left ventricular hypertrophy, and a history of cerebrovascular disease. The proportional hazards assumption was somewhat questionable for age greater than 69 years and left ventricular hypertrophy, which had slightly different hazard functions after 2 years. However, Weibul model regression results were virtually identical to Cox model results. The relative risks for the statistically significant risk factors (ranging from 2.1 for cerebrovascular disease to 1.5 for chronic obstructive pulmonary disease) are displayed in Table III. Figs. 1 through 5 display univariate Kaplan-Meier survival curves for each of these significant predictors of late survival and for the Goldman CRI. The joint effect of multiple clinical risk factors is illustrated by the 144 patients with Goldman CRI classification greater than one who had only a 58% 5-year survival rate and by the 34 veterans in this cohort age 70 years or older who had a history of chronic obstructive pulmonary disease and only a 44% survival rate 5 years after operation. Fig. 6 presents the overall survival of the DVA study cohort plotted against an age-matched expected survival curve based on all U.S. m e n for 1989. Expected survival was calculated from published 1989 hazard rates 18 for the male population and was weighted by the baseline age distribution of the AAA patient cohort. The survival for patients with AAA is quite comparable except for higher 1-year mortality and a slightly lower survival trend 4 years after operation.

Surgery Volume 118, Number 1

Feinglass et al.

19

T a b l e II. Kaplan-Meier survival probabilities by p a t i e n t risk factors

N (% of total) All patients Age > 69 yr* Age < 70 yr White Smoker Alcohol user Coronary artery disease Myocardial infarction Previous coronary artery bypass Congestive heart failure Cardiac arrhythmiat Cerebrovascular diseaset Claudication Renal artery involvement Aneurysm size+* >6.0 cm >7.0 cm Abdominal tenderness Urgent admission Diabetes mellitus Hypertension Left ventricular hypertrophy on electrocardiogram* Chronic obstructivet pulmonary disease Kidney diseaset Risk of pulmonary embolismw Dementia Liver disease Anesthesia physical classl I I

II III IV V TOTAL Goldman Cardiac Risk Indext I = 0-5 II = 6-12 III = 13-25 IV = >26 TOTAL

1-yr survival percentages (SE)

5-yr survival percentages (SE)

280 (100) 75 (27) 205 (63) 258 (92) 251 (90) 56 (20) 148 (53) 107 (38) 36 (13) 63 (23) 57 (20) 34 (12) 61 (22) 12 (4)

89 83 92 90 88 80 89 89 89 76 86 79 84 92

(2) (4) (4) (2) (2) (5) (3) (3) (5) (5) (5) (7) (5) (8)

64 52 68 64 63 59 66 66 69 58 52 49 60 50

(3) (6) (3) (3) (3) (6) (4) (5) (8) (6) (7) (8) (6) (14)

88 (35) 40 (16) 58 (21) 34 (12) 29 (10) 152 (54) 19 (7)

91 92 91 88 90 88 63

(3) (4) (4) (4) (6) (3) (11)

64 59 63 56 62 62 42

(5) (8) (6) (8) (9) (4) (11)

106 (38)

87 (3)

56 (5)

47 (17) 13 (5) 12 (4) 8 (3)

83 92 75 75

55 58 58 50

8 (3)

100

(5) (7) (12) (15)

40 (15) 191 (72) 26 (10) 1 (0.4) 266

93 (4) 90 (2) 85 (7) 0

136 (49) 70 (25) 73 (26) 1 (0.3) 280

94 (2) 85 (4) 84 (4) 100

(7) (5) (14) (18)

88 (12)

70 (7) 63 (4) 50 (10) 0

70 (4) 58 (6) 57 (6) 100

*p < 0.01.

tp< 0.05. ~n = 249 patients because of missing data for 31 padents (mean aneurism size = 5,98, SD = 1.54). w patients with history of pulmonary embolism, paraplegia, or hemiplegia. I In = 266 patients because of missing data for 14 patients.

COMMENT T h e 64% 5-year survival rate for this c o h o r t of male DVA patients is o n l y a p p r o x i m a t e l y 5% lower t h a n the male a n d female c o m b i n e d rates r e p o r t e d in most individual c e n t e r surgical case series f r o m the 1970s a n d

1980s. 8 As illustrated in Fig. 6, this is a n impressive result, given a m o r e severely ill DVA p o p u l a t i o n . As comp a r e d with p u b l i s h e d series, the v e t e r a n p a t i e n t c o h o r t s t u d i e d h e r e h a d h i g h e r rates of c o r o n a r y artery disease a n d c h r o n i c obstructive p u l m o n a r y disease with a 90%

20

Feinglass et al.

Surgery July 1995

1,0.9" .8" >

>

.7"

3

,6"

O0 > .

~q

%,

.5"

w

('o

.4"

E

.3"

6

Age Group > 69 years ,2"

n=75

.1"

0.0 0

~

1.2

14

3'6

4'8

6'0

7'2

g4

9'6

< 70 years n = 205

Survival Time in Monfhs Fig. 1, AAA late survival risk factor of age greater than 69 years.

1,0" .9" ,8"

> ~

3

.6 o

0.~ >

,5"

CO

.4-

E (_.)

Patient Group

.3-

COPD n=106

.2-

.1

No COPD

0.0

9'e

0

n = 174

S urvi val Time in Monfhs Fig. 2. AAA late survival risk factor of chronic obstructive pulmonary disease.

Table

IIIo Cox proportional hazards model results (N = 280)

Cerebrovascular disease Chronic obstructive pulmonary disease Left ventricular hypertrophy on electrocardiogram Age > 69 yr

Coefficient

SE

Relative risk

95 % Confidence interval

p Value

.54 ,44

.25 .18

1.72 1.55

(1.05-2.83) (1.07-2.25)

0.04 0.02

.76

.32

2.14

(1.14-4.02)

0.02

.47

.19

1.60

(1.09-2.36)

0.02

Surgery Volume 118, Number 1

Feinglass et al.

21

1.0" .9" .8"

.7"

3

%,6~

~ -I.-

.4"

E

Patient Group

.3"

Cerebrovascular

.2"

Disease n

.1

= 34

Cerebrovascular Disease n = 2 4 6

no

0.0 0

S urvi val Time in Months Fig. 3. A A A late survival risk factor of cerebro~rascular disease.

1.0,9-

.8" >

.7

3

.6

~ ~'" ~'" ~*~176_ . _ ~ - ~ - - ~- -*- - - - L _ I

i

,5(I]

E

.4-

Goldman CRI Class .3~

.2 o

C l a s s e s II - I V n=144

.1

~

Class I n=136

0.0

0

Survival Time in Months Fig. 4. AAA late survival risk factor of Goldman CRI class.

admitted smoking history. T h e slightly lower survival rate of patients in this study may also be related to referral biases, which inevitably tend to inflate survival statistics in m u c h of the AAA survival literature published from high-volume academic centers, l~ 20 O n the o t h e r hand, the 14 centers studied here may n o t be completely representative o f the overall DVA experience with AAA surgical procedures. T h e 30-day mortality rate for this c o h o r t of DVA patients was 2.9%. This rate compares very favorably to overall DVA Patient T r e a t m e n t File data for the p e r i o d when these opera-

tions occurred. O p e r a t i o n for repair o f u n r u p t u r e d AAA was associated with a 6.1% DVA inpatient mortality rate in FY 1985 (n = 1419) a n d a 7.7% DVA inpatient mortality rate in FY 1986 (n = 1451), for a 2-year cumulative hospital mortality rate o f 6.9%. As ofF]( 1985, 110 DVA medical centers were p e r f o r m i n g operations for m o r e than one patient with u n r u p t u r e d AAA for an average volume o f only 13 u n r u p t u r e d AAA p r o c e d u r e s p e r DVA medical center; only two DVA medical centers in the country p e r f o r m e d 30 o r m o r e u n r u p t u r e d AAA operations in FY 1985. T h e fact that the patient sample

22

Feinglass et al.

Surgery July 1995

1.0" .9" m

,8" > ~

>

.7"

I...

(1") QJ >

,6" o

,5"

. - -

.4'

Patient Group E

.3"

~ Left Ventricular Hypertrophy n = 19

,2" .1'

~ no Left Ventricular Hypertrophy n = 261

0.0 1'2

2'4

:36

48

6'0

7'2

8'4

96

Survival Time in Monfhs Fig. 5. AAA late survival risk factor of left ventricular hypertrophy.

1.0

0.8

09

0.6

OP :>

E 9

o.4 .......

0.2

0,0 0

US Male Survival Patient Survival

I

I

I

I

I

I

I

I

12

24

36

48

60

72

84

96

Survival Time in Months

Fig. 6. Kaplan-Meier survival probabilities. Patient versus age-matched U.S. 1989 male survival rates. studied here was drawn from 14 DVA medical centers with academic affiliations and relatively low mortality suggests that the overall survival experience in this study might have been better than the average for all DVA patients with AAA treated during the same period. O n e other DVA series on patients with AAA from the Los Angeles VA Medical Center reported only a 61% 5-year survival rate, although that study was limited to patients older than age of 60 years at the time of operation. 21

Numerous previous studies of AAA operations, including the two other studies that used multivariate proportional hazards models, 22' 23 have f o u n d clinically evident coronary artery disease (or previous myocardial infarction or cardiac abnormalities) to be significantly predictive of late survival. Given the likelihood of generalized atherosclerofic disease in patients with AAA, it is not surprising that "uncorrected" ischemic heart disease has consistently been found to be the leading cause

Surgery Volume 118, Number 1

of late mortality. 24 Although a history of cerebrovascular disease or left ventricular hypertrophy was a powerful predictor of late survival in this patient cohort, as was advanced G o l d m a n CRI class, it is difficult to explain the lack of significance in this study of a history of overt coronary artery disease or myocardial infarction. No data are available o n n o n o p e r a t e d patients with AAA seen at study hospitals. It is therefore impossible to rule out that these results simply reflect the fact that a comparatively greater proportion of DVA patients with AAA a n d advanced coronary artery disease were not offered operations. It should be noted, however, that a comparatively large proportion (53%) of patients in the study did have d o c u m e n t e d coronary disease a n d that more than one quarter of the sample fell into G o l d m a n CRI class III, indicating a comparatively poor prognosis. Although selection bias could have influenced the results, the most likely explanation for the coronary disease findings is the presence of unsuspected coronary disease a m o n g a substantial proportion of those DVA patients without a clear history of angina or myocardial infarction. Studies by investigators at Cleveland Clinic f o u n d that 86% of patients with peripheral vascular disease who did n o t have a clinically suggestive history of coronary disease were f o u n d to have coronary stenoses o n cardiac catheterization; 37% of these patients were f o u n d to have "advanced, compensated," or "severe" disease.25, 26 A review of angiographic data from three other studies involving 375 patients with AAA indicates a 65% average prevalence of "serious" coronary disease. 26 It should also be noted that in this study DVA patients with congestive heart failure a n d arrhythmias (who had substantially lower survival rates) were analyzed separately from patients with a history of coronary disease, whereas most other AAA late survival studies appear to group all heart disease or cardiac abnormalities together as a single heart disease risk factor. Finally, this study reports survival data o n one of the most recently operated AAA cohorts. Although these data remain speculative, these patients may have benefited from a relatively high rate of both previous a n d subsequent coronary artery bypass operation, angioplasty, a n d lipid-lowering drug therapy. A search of data for FYs 1984 through 91 from the VA Surgical Procedures file indicated that a total of 23 patients in the study u n d e r w e n t subsequent coronary artery bypass procedures at VA hospitals after their AAA operation. Two (8%), inpatient deaths occurred in this group, a n d a total of six (26%) of these patients died d u r i n g the 7-year follow-up period. Although the survival experience of this group was superior to that of the cohort as a whole, it is impossible to determine the true effect of more aggressive m a n a g e m e n t of coronary artery disease. Preoperative risk assessment has almost entirely fo-

Feinglass et al.

23

cused o n prediction of perioperative cardiovascular events. As shown by the significance of the G o l d m a n Cardiac Risk Index in this study, clinical risk scales can also have important implications for late survival. As improvements in imaging techniques reveal small aortic aneurysms in patients without symptoms, decisions about operative m a n a g e m e n t will increasingly be dep e n d e n t on patients' ability to weigh surgical risks against the probability of long-term benefit. 9' 27 Research on preoperative risk stratification should include methods a n d measures that improve clinicians' ability to communicate about late survival probabilities with elderly patients at higher risk. We acknowledge Shukri Khuri, MD, Chief of Surgery, Roxbur), Veterans Affairs Medical Center, and Dean Bross, PhD, Veterans Affairs Office of Quality Management, for their assistance in obtaining Veterans Affairs medical records from the Retrospective Surgical Mortality and Morbidity Risk Modeling Study. REFERENCES

1. Ernst CB. Abdominal aortic aneurysm. N Engl J Med 1993; 328:1169-72. 2. Agencyfor Health Care and PolicyResearch. Clinicalclassifications for health policyresearch: discharge statistics by principal diagnosisand procedure. ProviderStudiesResearch Note 17, US Departmentof Health and Human Services,AHCPRPublication 93-0043, August 1993. 3. Hannan EL, KilburnH, O'DonnellJF, et al. A logitudinalanalysisof the relationshipbetweenin-hospitalmortalityin NewYork State and the volume of abdominal aortic aneurysmsurgeries performed. Health Seta"Res 1992;27:517-42. 4. CollinJ, AraujoL, WaltonJ.Acommunitydetectionprogram for abdominalaortic aneur)~m.Angiology1990;January:53-7. 5. Lederle FA, WalkerJM, Reinke DB. Selective screening for abdominalaortic aneurysmwith physicalexaminationand ultrasound. Arch Intern Med 1988;148:1753-6. 6. GuirgnisEM, Barber GG. The natural historyof abdominalaortic aneurysms.AmJ Surg 1991;162:481-3. 7. Lederle F. Managementof small abdominal aortic aneurysms. Ann Intern Med 1990;113:731-2. 8. FeinglassJ, Pearce W, Martin GJ. Late sur~4valafter abdominal aortic aneurysmsurgery: a reviewof the literature.WestJ Med 1993;159:474-80. 9. KatzDA. Surgicaldecisionmaking:the repair of abdominalaortic aneur?~ms.WestJ Med 1993;159:502-3. 10. KatzDA, LittenbergB, CronenwettJL.Managementof smallabdominalaortic aneu.rysms:earlysurgeryversuswatchfulwaiting. JAMA 1992;268:2678-86. 11. WisselinkW, Hollier LH. Principlesand techniquesof endovascular graftingfor aneurysms.In:YaoJST, Pearce WH, eds. Aneurysms: new findingsand treatments.Norwalk,Connecticut:Appleton & Lange, 1993:317-24. 12. SystemSciencesInc. Final report, contract no V101(93)P-1206, Department of VeteransAffairs,Office of QualityManagement, Washington DC,June 1989. 13. GoldmanL. Cardiac risksand complicationsof non-cardiacsurgeD'. Ann Intern Med 1983;98:504-13. 14. Dripps RD, Lamont A, EckenhoffJE. The role of anesthesia in surgical mortality.JAMA 1961;178:261-6.

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15. McEnroe CS, O'Donnell TF, Yeager A, Konstam M, MackeyWC. Comparison of ejection fraction and Goldman risk factor analysis to dipyridamole-thallium 201 studies in the evaluation of cardiac morbidity after aortic aneurysm surgery.J Vase Surg 1990;11: 497-504. 16. Abraham SA, Coles, NA, Coley CM, Strauss HW, Boucher, CA, Eagle KA. Coronary risk of non-cardiac surgery. Prog Cardiovasc Dis 1991;34:205-34. 17. KalbfleischJD, Prentice RL. The statistical analysisof failure time data. New York: John Wiley and Sons, 1980. 18. National Center for Health Statistics.Vital statisticsof the United States, 1989: life tables, vol. II, Section 6, DHHS publication no (PHS) 93-1104. US Department of Health and Human Services, 1992. 19. Veith FJ, Goldsmith J, Leather RP, Hannan EL. The need for quality assurance in vascular surgery.J Vase Snrg 1991; 13:523-6. 20. Melton LJ. Selection bias in the referral of patients and the natural history of surgical conditions. Mayo Clin Proc 1985; 60:880-9. 21. White GH, Advani S, Williams RA, Wilson SE. Cardiac risk index as a predictor of long-Lerm s ~ after repair of abdominal aortic aneurysm:Am J Surg 1988;156:103-7.

Surgery July 1995 22. Roger VL, Ballard DJ, Hallett JW, Osmundson PJ, Puetz PA, Gersh BJ. Influence of coronary artery disease on morbidity and mortality after abdominal aortic aneurysmectomy: a population-based study, 1971-1987.JAm Coll Card 1989; 14:124552. 23. Johnston KW. Canadian study of late results of abdomonal aortic aneurysm repair. In: YaoJST, Pearce WH, eds. Aneurysms: new findings and treatments. Norwalk, Connecticut: Appleton & Lange, 1993:79-87. 24. Freeman WK, Gersh BJ, GloviczkiP. Abdominal aortic aneurysm and coronary artery disease: frequent companions, but an uneasy relationship. J Vase Surg 1990;12:73-7. 25. Young JR, Hertzer NR, Beven EG, et al. Coronary artery disease in patients with aortic aneurysm: a classification of 302 coronary angiograms and results of surgical management. Ann Vase Snrg 1986;1:36-42. 26. Hertzer NR. Basicdata concerning associated coronary disease in peripheral vascular patients. Ann Vase Surg 1987;1: 616-20. 27. Scott RAP,Wilson NM, Ashton HA, Kay DN. Is surgery necessary for abdominal aortic aneurysm less than 6 cm in diameter? Lancet 1993;342:1395-6.

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