National trends in the repair of ruptured abdominal aortic aneurysms
Article Outline
Objective
This study evaluated trends in hospitalizations, treatment, and mortality of ruptured abdominal aortic aneurysms (rAAAs) in the United States Medicare population.
Methods
The Medicare inpatient database (1995 through 2006) was reviewed for patients with rAAA and AAA by using International Classification of Disease (9th Clinical Modification) codes for rAAA and AAA. Proportions and trends were analyzed by χ2 analysis, continuous variables by t test, and trends by the Cochran-Armitage test.
Results
During the study period, hospitalizations with the diagnoses of rAAA declined from 23.2 to 12.8 per 100,000 Medicare beneficiaries (P < .0001), as did repairs of rAAA (15.6 to 8.4 per 100,000; P < .0001). No change was observed in AAA elective repairs. The 30-day mortality rate after open repair of rAAA decreased by 4.9% (from 39.6% to 34.7%; P = .0007 for trend) for the age group 65 to 74 and by 2.4% (from 52.9% to 50.5%, P = .0008) for the age group ≥75. Perioperative mortality after endovascular repair diminished by 13.6% (from 43.5% in 2001 to 29.9% in 2006; P = .0020). Mortality among women was higher than among men (51.1% vs 40.0% in 2006). The demographics of patients treated for rAAA changed to include a greater proportion of women and patients aged ≥75 years.
Conclusion
A significant decrease has occurred in the number of patients who have a diagnosis of rAAA and undergo treatment, but there has been no change in repairs of AAA. The perioperative mortality rate has improved due to the introduction of endovascular repair and a small but progressive improvement in survival after open repair for patients aged 65 to 74 years.
Ruptured abdominal aortic aneurysm (rAAA) remains among the most morbid diagnoses in vascular surgery.1 Significant morbidity and mortality persists despite advances made in the repair of intact abdominal aortic aneurysms (AAAs). During the last decade there has been a surge in the use of endovascular techniques to treat AAAs. The morbidity and mortality associated with elective endovascular AAA repair (EVAR) is diminished compared with open repair.2, 3 This reduction in mortality after intact EVAR was also observed for rAAAs undergoing EVAR in many centers.4
Two major factors could potentially have influenced the overall frequency of aneurysm repair. The minimally invasive endovascular treatment may be a more attractive alternative to patients. EVAR also allows for the repair of AAAs in patients previously deemed unfit for open repair because the perioperative event rate is significantly less than conventional repair of AAAs.5, 6 In contrast to these incentives, which support a higher utilization of AAA repair, the threshold for repair of intact AAAs has evolved from 4.5 to 5.5 cm on the basis of two recently published “small aneurysm” studies.7, 8
The ultimate goal of aneurysm detection and treatment is to prevent rupture and its consequence, which is usually death. Thus, an appropriate surrogate for the effectiveness of our efforts to treat AAA in the United States would be the frequency that patients are hospitalized or treated for rAAA. A previous report from our group using the Nationwide Inpatient Sample (NIS) database revealed that during a 20-year period from 1979 to 2002, the frequency of treatment of intact AAA did not change.2 We recently acquired the Medicare database for the years 1995 through 2006, which contains all discharges and longitudinal information for Medicare fee-for-service patients. Given the stable rates of elective AAA repair, surgical advances, and changes in demographics, we used the Medicare data set to address whether the frequency of rAAA and its mortality has changed in recent years.
Methods
Data sources and study population
The Medicare Inpatient Standard Analytical files from 1995 through 2006 were used to identify discharges with the International Classification of Diseases (ICD-9-CM) diagnoses code of 441.3 (aortic abdominal aneurysm, ruptured, any position) or 441.4 (aortic abdominal aneurysm without mention of rupture, any position). The Medicare Inpatient Standard Analytical file contains data on all Medicare-reimbursed hospitalizations, except those delivered to beneficiaries enrolled in Medicare-administered health maintenance organizations (HMOs). Approximately 10% (7.1% in 1994 and 17% in 2006) of elderly and disabled patients were enrolled in a Medicare HMO and were not included in this study. The data were obtained from the Center for Medicare and Medicaid Services through the Research Data Assistance Center (resdac@umn.edu).
The Medicare Inpatient Standard Analytical file is a national data set derived from hospital discharge abstracts. The data set includes patient demographics, admission type, discharge disposition, hospital and provider information, patient diagnoses (admitting, primary, and up to 10 secondary diagnoses), procedures (up to 6), and detailed charge data.
The Inpatient Standard Analytical files were supplemented with Medicare Denominator files from 1995 through 2006. The Denominator file contains demographic, geographic, and vital status data on all Medicare beneficiaries as well as an indicator of HMO participation. The number of patients enrolled in a Medicare HMO or a fee-for-service program, gender distribution by year, and patient date of death were derived from Denominator files (http://www.cms.hhs.gov/MedicareMedicaidStatSupp/downloads/2007Table2.1b.pdf).
Patients who had an ICD-9-CM diagnosis of rAAA or AAA without mention of rupture (in any position) were included in this analysis. Those who underwent repair were identified with the ICD-9-CM procedural codes detailed in the Table, in either a primary or secondary position. The number of discharges for patients who had AAA as one of their multiple diagnoses was used as a surrogate of AAA frequencies. We assumed that the higher the prevalence of AAA, the higher the number of patients hospitalized with this diagnosis.
Table. International Classification of Diseases, 9th Clinical Modification, diagnostic and procedural codes used to derive the study population
| Code | Description |
|---|---|
| Diagnostic | |
 441.3 | Aortic abdominal aneurysm, ruptured |
| 441.4 | Aortic abdominal aneurysm without mention of rupture |
| Procedural | |
| 39.71 | Endovascular implantation of graft in abdominal aorta |
| 38.44 | Resection of abdominal aorta with replacement |
| 39.25 | Aorta-iliac-femoral bypass |
| 39.52 | Other repair of aneurysm |
| 38.34 | Resection of abdominal aorta with anastomosis |
| 38.64 | Other excision of abdominal aorta |
| 38.40 | Resection of vessel with replacement, unspecified site |
| 38.60 | Other excision of vessels, unspecified site |
Statistical analysis
The rates for total number of discharges and number of AAA repairs were calculated by dividing the total number of discharges with AAA diagnoses or procedures, respectively, by Medicare population enrolled in fee-for-service program. All rates were expressed per 100,000 Medicare fee-for-service beneficiaries population. A subgroup analysis of hospitalizations with rAAA diagnoses or rAAA repairs by gender was also performed. Univariate analyses were conducted using t tests for continuous variables and χ2 or the Fisher exact test for dichotomous variables. Confidence intervals (CIs) for rates were calculated using normal approximation to the binomial distribution. Linear regression analysis was used to analyze trends in per capita hospitalizations. The Cochran-Armitage test was used for trend analysis. Statistical significance was expressed as both P values and 95% CIs. Values of P < .05 were considered significant. All statistical analyses were performed using SAS 9.1 software (SAS Institute Inc, Cary, NC).
Results
Medicare is a federal insurance program that provides coverage for Americans aged >65 and for the disabled. The number of beneficiaries enrolled in fee-for-service Medicare programs increased from 34 million in 1994 to 35.5 million in 2006. In this time period, 4,339,886 hospitalizations were identified with a diagnosis of AAA. Among these were 74,686 (1.7%) hospitalizations with the diagnoses of rAAA. During the same time period, 50,996 repairs of rAAAs (2115 endovascular and 48,881 open procedures) were performed for 50,824 patients (71.6% male). Of all patients admitted with a rAAA, 93.01% were white, 4.45% were African American, and 2.54% were of other ethnicities. The age of patients hospitalized for a rAAA increased significantly, from 76.6 years in 1995 to 78.4 years in 2006 (P < .0001).
We first queried whether there had been a change in the frequency of AAA rupture during the period of observation. From 1995 through 2006, there was a significant decrease in both the number of hospitalizations with the diagnosis and interventions for rAAA (Fig 1, A). The decline in hospitalizations was from 23.18 to 12.81 per 100,000 during study period (P < .0001 for trend; r2 = .9695). The decline in rAAA repair was from 15.64 to 8.45 per 100,000 Medicare beneficiaries during the same time (P < .0001 for trend; r2 = .9695). Because both admissions for the diagnosis of and repair for rAAA declined in parallel, the ratio of hospitalizations for rAAA diagnoses compared with rAAA interventions was constant throughout the study period (approximately 66% to 69%; Fig 1, B).
Fig 1.
Trends in (A) the hospitalizations with diagnoses (black circles) and repairs (white circles) of ruptured abdominal aortic aneurysms (rAAA) and p(B) ratio of repairs (open circles) to hospitalizations with rAAA diagnoses among Medicare beneficiaries from 1995 through 2006.
From 1995 through 2006, the total number of hospitalizations with the diagnosis of AAA increased from 296 to 341 per 100,000 Medicare beneficiaries (P = .0013; r2 = .7436). However, the number of elective AAA repairs remained stable for the period of observation, at approximately 83 per 100,000 Medicare beneficiaries (P = .1746; r2 = .1193; Fig 2). The decline in the frequency of admissions for rAAA was notable and significant in both men and women, albeit significantly more pronounced in men. Paralleling the known gender differential in incidence of AAA, we found that men were more likely to undergo repair of a rAAA than women (Fig 3, A). In 1995 men were diagnosed with rAAA at a rate of 40 per 100,000 male beneficiaries. This number declined to 19 by 2006 (52% decrease in hospitalizations; P < .0015). The number of women diagnosed with rAAA also decreased during the study period, but to a lesser degree, from 11 to 7 per 100,000 female beneficiaries (26% decrease; P < .0001; Fig 3, A). The ratio of interventions to hospitalizations for rAAA averaged 73% in men and 56% in women (Fig 3, B). These data show that when women are admitted with the diagnosis of rAAA, they are less likely to be treated.
Fig 2.
Trend in (A) the hospitalizations with diagnoses (black circles) and repairs (white circles) of intact abdominal aortic aneurysms (iAAA) and in (B) the ratio of interventions (black circles) to hospitalizations with iAAA diagnoses among Medicare beneficiaries from 1995 through 2006.
Fig 3.
Trends in (A) the diagnoses and repairs of ruptured abdominal aortic aneurysm (rAAA) hospitalizations and in (B) the ratio of interventions to hospitalizations for men (black symbols) and women (white symbols). 1, hospitalizations with diagnoses of rAAA for men; 2, hospitalizations with diagnoses of rAAA for women; 3, repairs of rAAA for men; 4, repairs of rAAA for women.
From 1995 through 2006, the age of men hospitalized with a rAAA increased from 75 to 77 (P < .0001), and the age for women increased from 79 to 81 (P < .0001). The mean age during the entire study period was 76.4 years for men (95% CI, 76.3-76.4 years) vs 79.9 years for women (95% CI, 79.8-80.0 years; P < .0001).
During the study period, the age composition of patients who underwent repair changed. The percentage of patients aged 65 to 74 decreased progressively from 49.7% in 1995 to 38.7% in 2006, with a parallel increase in patients aged '75 from 50.3% in 1995 to 61.3% in 2006. Although an increase in mortality might be expected with increasing patient age, there was no change in perioperative mortality after open repair (P = .3101 for trend) and a progressive decrease in mortality after EVAR since 2001 (Fig 4, P = .0020 for trend). Interestingly, when we stratified open mortality by age groups, we observed a modest but progressive improvement in perioperative survival for patients aged 65 to 74 (P = .0007 for trend) as well as for older patients (P = .0008 for trend; Fig 5).
Fig 4.
Trend in 30-day mortality after ruptured abdominal aortic aneurysms repair with open (black circles) and endovascular (endo, white circles) repairs. Error bars indicate 95% confidence interval.
Fig 5.
Change in 30-day mortality after ruptured abdominal aortic aneurysm repair by patients aged 65 to 74 years (white circles) and those aged ≥75 years (black circles). Error bars indicate the standard deviation.
A gender differential was also identified in mortality rates after repair of rAAA. The average mortality rate after repair of rAAA was 43.5% in men and 52.3% in women (P < .0001). This difference was 8% (95% CI, 4.73%-11.25%) in 1995 and 11% (95% CI, 7.07%-15.28%) in 2006, which was not an improvement over time (Fig 6).
Fig 6.
Trend in 30-day mortality after ruptured abdominal aortic aneurysm repair for men (black circles) and women (white circles).
Discussion
Rupture of an AAA is associated with a grim prognosis. The overall mortality rate after rupture is estimated at up to 90%,9, 10 and only 50% of those patients who are hospitalized for rAAA survive surgical intervention.10, 11, 12, 13 This is in vast contrast with the outcomes for repair of intact AAAs, where the operative mortality is 2% to 8%.13 Estimates of the incidence of rAAA vary widely, and little is known about recent trends in the number of rAAAs diagnosed and treated. Most ruptures occur out of the hospital, and consequently, it is impossible to measure their frequency. We therefore used the number of patients that were hospitalized and treated for rupture as a surrogate for the frequency of rAAA.
In 1995, 23.2 patients per 100,000 Medicare beneficiaries were hospitalized with diagnoses of a rAAA. During the 12 years analyzed in the current study, the number of hospitalizations of rAAA decreased to 12.8 per 100,000 beneficiaries (P < .0001). This is likely a significant under-representation of the actual number of patients who succumbed to rAAA because most patients die before receiving medical attention. The number of patients who underwent intervention for rAAA also dramatically decreased during the same 12-year period. Cowan et al,14 using the National Impatient Sample (NIS) database from 1993 to 2003, identified 14,642 rAAA repairs and found the rates of rAAA to be stable at 1 to 3 per 100,000 capita. The higher rate of interventions reported in our study reflects the higher risk of interventions among the population of Medicare beneficiaries compared with the general population of the NIS database. In an evaluation of a 5% sample of the Medicare beneficiary data (Beneficiary Encrypted File), rAAA repairs decreased from 18.7 per 100,000 in 1994 to 13.6 per 100,000 in 2003.15 This parallels our data that show these rates to be 15.6 per 100,000 Medicare beneficiaries in 1995 and 8.4 per 100,000 beneficiaries in 2006.
This decrease in both hospitalizations and procedures for rAAA coincided with an increase in the number of hospitalizations for intact AAA from 296 in 1995 to 341 per 100,000 beneficiaries in 2006 (P < .0001). It thus appears that more aneurysms are being identified, or at least more patients are being hospitalized with AAA as one of their diagnoses. It might be hypothesized that the observed decrease in rAAA would also coincide with an increase in the number of intact AAA repairs. Presumably, elective repair of large aneurysms prevents subsequent rupture. Another potential explanation for the increase in number of admissions for the diagnosis of AAA is that there has been shown to be not an insignificant increase in readmissions for patients who have EVAR, and those patients may be inflating the admission pool of those patients with the diagnosis of AAA. Our study was based on total patient admissions and not specific patients. Perhaps screening programs or the variety of noninvasive imaging tests that are now available have led to the more frequent discovery of large aneurysms that were then treated electively and not allowed to rupture.16, 17, 18 If this were true, the number of repairs of intact AAA would be increasing. However, analysis of the Medicare data set does not show this to be the case, as the number of intact AAA repairs has remained stable from 1995 through 2006 (Fig 2).
As previously mentioned, many changes have occurred in treatment of aneurysms during the past decade, including the introduction of EVAR and a major shift in the threshold for aneurysm repair. Hidden within the demonstrated stable rate of intact AAA repair may be patients with large aneurysms (>5.5-cm diameter) previously deemed unfit for open repair that are now being treated with EVAR, coinciding with increasing nonsurgical observation for small aneurysms because of the new threshold.7, 19 These two simultaneous changes in the inclusion and exclusion of AAA patients for repair may be responsible for the constant rate of overall intact AAA repair. Because large data sets do not provide information about the size of aneurysms at the time of repair, it is impossible with the data we have available to test this hypotheses.
Previous studies of perioperative mortality rates after rAAA reported different trends: Bown et al20 reported a reduction in open operative mortality of approximately 3.5% per decade during a prolonged period (1954 to 1997) derived by meta-regression analysis, whereas for a more recent period (1994 to 2003), Dillavou et al15 observed a stable overall mortality rate. Our study identified a statistically significant drop that occurred from 1995 through 2006 in overall 30-day mortality after repair of rAAA, which included a decreasing mortality rate after EVAR and a stable mortality rate after open repair (Fig 4).
We observed a similar progressive decline in mortality (3.7% over a decade) as described by Bown for patients aged 65 to 74 as well as for patients aged ≥75 in open repair (Fig 5). However, overall mortality after open repair remained stable due to the growing proportion of patients aged ≥75, whose mortality rate is about 15% higher than for patients aged 65 to 74.
Dillavou et al,15 who focused on a more recent decade than Bown et al,20 reported a stable overall mortality rate. The reason of the difference between our results and the Dillavou et al results may be due to the use of different methodology. Dillavou et al used a 5% sample of Medicare data and in-house mortality, whereas our study used a more through evaluation of 100% Medicare hospitalizations with a 30-day mortality calculation. Our study also included an additional year of observation, which encompasses the survival improvement of patients who had EVAR and the growing use of this procedure for rAAA repair.
When we evaluated the effect of EVAR on death, our results agreed with other studies that found a beneficial effect of EVAR in rAAA.21, 22 Increased usage of this technology will likely sustain continuous improvement in survival in the future.
A number of substantial differences between men and women with regard to rAAA were observed in the current analysis. The number of men admitted with rAAA significantly decreased (52.5%) during the period studied. This decrease was responsible for the overall decrease in the number of rAAA admissions because a similar trend was not observed in women. In addition to a gender differential in the diagnosis of rAAA, a gender differential was also noted in the percentage of patients who came to intervention for a rAAA, because men were more likely to undergo repair than women. We also observed a gender differential in death after repair of rAAA. The average mortality rate after repair of rAAA in men was lower than in women. These findings confirm results previously reported by others.15, 23, 24
One might conclude from the current results that we have made progress in our ability to treat aneurysms in men, but not in women. There are a number of possible reasons for this differential. Perhaps due to the lower incidence of AAA in women, we have not been as attentive to women with our screening efforts. Alternatively, we may be using an incorrect threshold when recommending aneurysm repair in women; it has been demonstrated that aneurysms in women rupture at a smaller size than in men.25, 26 Reasons for the discrepancy in rates of treatment may include the fact that women are significantly older at the time of presentation for rupture and often have more complex anatomy than men, with short infrarenal necks and diseased and small iliac vessels making them less likely to be offered EVAR and more likely to have complex open repairs or be observed. Nevertheless, none of these limitations seem sufficient to deter attempts at aneurysm repair in women with rupture considering that the alternative is death. Regardless of the reason, these data suggest that we need to focus on ways to decrease the incidence of rupture in women and to ensure that when women are admitted for rupture, they are treated equally.
There are limitations associated with the use of large data sets. The Medicare data set used in this study includes only patients aged >65. However, studies that use alternate data sets such as the NIS, which samples a broader population, have reached similar conclusions. Specific drawbacks to the use of administrative data sets include the lack of information about the severity of comorbidities. Diagnosis codes are broad and provide limited detail about the specific disease state.
An additional limitation important to the analysis of the current data set is the lack of information about patient anatomy. We are not able to identify which of these patients had diseased iliac arteries, nor do we know the size of the aneurysms treated.
Lastly, as with all administrative data sets, there is the potential for coding inaccuracies and oversights.27 The effect of coding issues is likely diminished by the “randomization” of systematic errors that results when massive numbers of observations are statistically analyzed.6 These limitations aside, the distinct advantage of administrative data bases such as this Medicare data set, is the large sample size.
Conclusions
A significant decrease in the number of Medicare admissions and procedures for rAAA was identified. Differing from previous reports, we are seeing a continued gradual diminution in the 30-day mortality associated with rAAA repairs. Our study found a more dramatic decrease in rAAA mortality in those patients who were treated with EVAR. These data suggest that we are making progress in our ability to treat aneurysmal disease, since prevention of rupture is the ultimate goal. The reason for this success is not completely clear, although one must concluded that large and potentially dangerous aneurysms are being identified and treated more frequently.
Our success in the treatment of aneurysms, thus far, has been confined to men, suggesting the need to reevaluate our approach to aneurysmal disease in women. Despite the progress that has been made, a large number of individuals still succumb to aneurysmal disease. The overwhelming mortality associated with rAAA strongly supports the development of screening programs to identify patients at high risk for AAA and evaluation of their cost-effectiveness.
Author contributions
References
- . Surgery for ruptured abdominal aortic aneurysm: early and late results of a prospective study by the AURC in 1989. Ann Vasc Surg. 1997;11:90–99
- Trends, complications, and mortality in peripheral vascular surgery. J Vasc Surg. 2006;43:205–216
- A randomized trial comparing conventional and endovascular repair of abdominal aortic aneurysms. N Engl J Med. 2004;351:1607–1618
- Outcomes of endovascular treatment of ruptured abdominal aortic aneurysms. J Vasc Surg. 2006;43:453–459
- . Comparison of endovascular aneurysm repair with open repair in patients with abdominal aortic aneurysm (EVAR trial 1), 30-day operative mortality results: randomized controlled trial. [see comment] Lancet. 2004;364:843–848
- . Perioperative outcomes after open and endovascular repair of intact abdominal aortic aneurysms in the United States during 2001. J Vasc Surg. 2004;39:491–496
- Immediate repair compared with surveillance.of small abdominal aortic aneurysms. N Engl J Med. 2002;19:1437–1444
- The UK Small Aneurysm Trial Participants (Mortality results for randomised controlled trial of early elective surgery or ultrasonographic surveillance for small abdominal aortic aneurysms). Lancet. 1998;352:1649–1655
- . Ruptured abdominal aortic aneurysm: a population-based study. J Vasc Surg. 1993;18:74–80
- . Abdominal aortic aneurysm. N Engl J Med. 1993;328:1167–1172
- . Survival after ruptured abdominal aortic aneurysm: effect of patient, surgeon, and hospital factors. J Vasc Surg. 2004;39:1253–1260
- . Long-term survival and health-related quality of life of patients with ruptured abdominal aortic aneurysm. Eur J Vasc Endovasc Surg. 2003;25:350–353
- The epidemiology of surgically repaired aneurysms in the United States. J Vasc Surg. 1999;30:632–640
- . Epidemiology of aortic aneurysm repair in the United States from 1993 to 2003. Ann N Y Acad Sci. 2006;1085:1–10
- . A decade of change in abdominal aortic aneurysm repair in the United States: Have we improved outcomes equally between men and women?. J Vasc Surg. 2006;43:230–238
- Aneurysm Outreach Inc., a nonprofit organization, offers community-based, ultrasonography screening for abdominal aortic aneurysms. Ann N Y Acad Sci. 2006;1085:291–293
- . Screening for abdominal aortic aneurysm: recommendation statement. [see comment] Ann Intern Med. 2005;142:198–202
- . Welcome to Medicare visit and AAA screening. [comment] Fam Pract Manage. 2007;14:16;; author reply 16.
- Early elective open surgical repair of small abdominal aortic aneurysms is not recommended: results of the UK Small Aneurysm Trial (Steering Committee). Eur J Vasc Endovasc Surg. 1998;16:462–464
- . A meta-analysis of 50 years of ruptured abdominal aortic aneurysm repair. Br J Surg. 2002;89:714–730
- Endografting increases total volume of AAA repairs but not at the expense of open surgery: experience in more than 1000 patients. J Endovasc Ther. 2005;12:274–279
- . Improving aneurysm-related outcomes: nationwide benefits of endovascular repair. J Vasc Surg. 2006;43:446–451discussion 451-2.
- . Influence of gender on outcome from ruptured abdominal aortic aneurysm. [see comment] Br J Surg. 2000;87:191–194
- . Gender differences in abdominal aortic aneurysm prevalence, treatment, and outcome. J Vasc Surg. 1997;25:561–568
- . Gender differences in relative dilatation of abdominal aortic aneurysms. Ann Vasc Surg. 2006;20:564–568
- Gender-related differences in the tensile strength of abdominal aortic aneurysm. Ann N Y Acad Sci. 2006;1085:400–402
- The accuracy of Medicare's hospital claims data: progress has been made, but problems remain. Am J Public Health. 1992;82:243–248
Competition of interest: none.
PII: S0741-5214(08)01024-0
doi:10.1016/j.jvs.2008.06.031
© 2008 The Society for Vascular Surgery. Published by Elsevier Inc. All rights reserved.
