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Logo of nihpaAbout Author manuscriptsSubmit a manuscriptHHS Public Access; Author Manuscript; Accepted for publication in peer reviewed journal;
 
J Vasc Surg. Author manuscript; available in PMC 2013 September 1.
Published in final edited form as:
PMCID: PMC3422605
NIHMSID: NIHMS363809

Superior Outcomes for Rural Patients After Abdominal Aortic Aneurysm Repair Supports a Systematic Regional Approach to AAA Care

Matthew W. Mell, MD,1 Christie Bartels, MD,2 Amy Kind, MD,2 Glen Leverson, PhD,2 and Maureen Smith, MD, PhD, MPH2

Abstract

Objectives

The impact of geographic isolation on abdominal aortic aneurysm (AAA) care in the U.S. is unknown. It has been postulated but not proven that rural patients have less access to endovascular aneurysm repair (EVAR), vascular surgeons, and high volume treatment centers than their urban counterparts, resulting in inferior AAA care. The purpose of this study was to compare the national experience for treatment of intact AAA for patients living in rural areas or towns with those living in urban areas.

Methods

Patients who underwent intact AAA repair in 2005–2006 were identified from a standard 5% random sample of all Medicare beneficiaries. Data on patient demographics, co-morbidities, type of repair and specialty of operating surgeon were collected. Hospitals were stratified into quintiles by yearly AAA volume. Primary outcomes included 30-day mortality and rehospitalization.

Results

A total of 2616 patients had repair for intact AAA (40% open, 60% EVAR). Rural and urban patients were equally likely to receive EVAR (rural 60% vs. urban 61%, p=.99) and be treated by a vascular surgeon (rural 48% vs. urban 50%; p=.82). Most rural patients (86%) received care in urban centers. Primary outcomes occurred in 11.6% of rural patients (1.3% 30-day mortality, 10.3% re-hospitalization) versus 16.0% of urban patients (3% 30-day mortality, 13% rehospitalization; p=.04). In multivariate analyses, rural residence was independently associated with treatment at high-volume centers (OR 1.64, 95% CI 1..34 – 2.01; p<.0001) and decreased death or re-hospitalization (OR 0.69, 95% CI .49 – .97; p = .03).

Conclusions

Despite geographic isolation, patients in rural areas needing treatment for intact AAA have equivalent access to EVAR and vascular surgeons, increased referral to high-volume hospitals, and improved outcomes after repair. This suggests that urban patients may be disadvantaged even with nearby access to high quality centers. This study supports the need for criteria that define centers of excellence to extend the benefit of regionalization to all patients.

Introduction

Abdominal aortic aneurysm (AAA) represents a significant ongoing health concern for the elderly population. Several factors have been associated with improved outcomes after AAA repair, including endovascular aneurysm repair (EVAR), surgery performed in high-volume centers, and surgery by those with specialized vascular training15. No prior studies have examined the availability of this level of AAA care for the 15–20% of the U.S population that lives in rural areas. However, rural patients have reduced access to health care; and studies of other complex medical conditions such as cancer have found that rural patients are disadvantaged compared with their urban counterparts6,7 with regard to initial stage, initial treatment, post-treatment surveillance, and participation in clinical trials. Other studies have shown that ethnicity and insurance type influence access to high volume center and surgical outcomes after AAA repair.8, 9

Using patient-level data, we aimed to describe the national experience for treatment of intact AAA for patients living in rural areas; identify differences in treatment characteristics between rural and urban AAA patients; and determine the effect of treatment differences on outcomes. We hypothesized that patients residing in rural areas or towns would be less likely to undergo EVAR, less likely to be treated in a high-volume center or by a vascular surgeon, and would experience higher mortality and readmissions.

Methods

The study was conducted as a retrospective analysis using data of Medicare beneficiaries who underwent surgery for intact AAA in 2005–2006. Data were obtained from the Centers for Medicare & Medicaid Services (CMS) through the Chronic Condition Data Warehouse (CCW), administrated by the Iowa Foundation for Medical Care. This dataset includes a random 5% sample of all Medicare patients in the United States, and unique to the CCW, any beneficiary that enters the cohort will remain in the cohort from that time forward. Inpatient files, outpatient files, and denominator files were available for data extraction. Each record included demographics, physician and hospital identifiers, and diagnosis and procedure codes as classified by the International Classification of Diseases, 9th Clinical Modification (ICD-9, CM).

The included patients were Medicare beneficiaries receiving surgical treatment for AAA between 1/1/05 and 12/1/06 that had been continuously enrolled in Medicare Part A and Part B for at least 365 days prior to the date of the index procedure to allow full characterization of baseline comorbidities. Patients with a diagnosis of intact AAA (ICD 9-CM codes 441.4, 441.9) and an open or endovascular procedural code during the index hospitalization (codes 38.34, 38.44, 38.64, 39.52, 39.71) were analyzed. Ruptured aneurysms (441.3) were excluded, as were aortic dissections, thoracic aneurysms, or thoracoabdominal aneurysms, or aneurysm diagnoses without an associated treatment code. Also excluded were those with incomplete enrollment in Medicare Part A (hospital claims) and B (physician claims) for 12 months preceding surgery, enrollment in a Medicare HMO, or having railroad benefits at any time from entry into Medicare through 12/31/2006.

Patient demographic data collected included age, sex, race, and eligibility for Medicaid during the study period. Patient co-morbidities were estimated using the Centers for Medicare and Medicaid Services - Hierarchical Condition Categories (HCC) scale 1013. This validated measure of co-morbidity uses 12 months of inpatient and ambulatory claims to calculate predicted expenditures in future years. Over 3000 ICD-9-CM diagnosis codes are divided into 70 Condition Categories (CC)10. Within each CC hierarchies are used to characterize each person’s level of illness within each disease process. For example, within the Coronary Artery Disease hierarchy, 4 CCs are arranged in descending order of clinical severity and cost, from CC 81 Acute Myocardial Infarction to CC 84 Coronary Atherosclerosis. A patient with an ICD-9-CM code within CC 81 is excluded from being coded in CCs 82–84 even if codes within these groups are present.

HCC also accounts for significant interactions between CC categories that have substantial effects on cost. For example, simultaneous presence of CHF and COPD leads to higher costs than would be predicted by adding predicted increments of CHF and COPD alone. The score therefore is an estimation of the presence of and severity of medical co-morbidity, as patients with more medical conditions and increased illness for a given condition will incur more medical expenses. By convention, a score of 1 represents the predicted cost of an average Medicare patient.

Residence was grouped into rural, large town or urban using US Department of Agriculture census-based Rural Urban Commuting Area (RUCA) codes 14, 15. Each ZIP code was converted to a RUCA code based on both population size and commuting patterns, and has advantages over previous classification systems in that less densely populated ZIP codes adjacent to or within metropolitan areas are not miss-classified as rural areas. Additionally, differences within counties (for example one urban ZIP code surrounded by rural ZIP codes) are captured. Rural areas were defined as population of less than 10,000 and included RUCA codes 7, 7.3, 7.4, 8, 8.3, 8.4, 9, 9.1, 9.2, 10, 10.3, 10.5. Large towns (population 10,000 – 50,000) included RUCA codes 4, 5, 6, 7.2, 8.2, 10.2 and urban areas (population >50,000) included RUCA codes 1, 2, 3, 4.1, 7.1, 8.1, 10.1.

Treatment variables included type of AAA repair, yearly hospital AAA repair volume, and operating physician specialty. The primary outcome variable was 30-day mortality or rehospitalization within 30 days of the primary procedure. Yearly hospital volume was categorized into quintiles, based on work by Birkmeyer et al16. Hospitals in the highest quintile were defined as high volume hospitals. Physician specialty was determined by unique physician identifier number (UPIN).

Variables were compared with chi square, Fisher’s exact test, t-test, ANOVA, or Wilcoxon rank sum test when indicated. Data were considered statistically significant with a P-value ≤ .05. Multivariable hierarchical mixed effects regression models were then used to determine independent correlates for treatment and outcome variables and to adjust for clustering at the hospital level. Statistical analysis was performed using SAS version 8.0 (Cary, NC).

RESULTS

A total of 2616 patients were identified who underwent repair for intact AAA in 2005 – 2006. Mean age was 75.8 +/− 6.5. Three fourths of patients were male, and 94% were Caucasian. Medically indigent patients, defined as those eligible for Medicaid at any time during the study period, made up 8.5% of the sample.

Most patients (n =1845, 70%) resided in urban areas. Rural patients (n=388) and large town patients (n=383) each accounted for 15% of the cohort. Comparing patients by type of residence (TABLE 1), rural patients were more likely to be Caucasian and more likely to receive Medicaid than their large town or urban counterparts. No significant differences existed with regard to co-morbidity score.

TABLE 1
Demographics

The vast majority of procedures (93.9%) were performed in urban centers; and this was true regardless of type of residence. However, rural patients (86.1%) and large town patients (77.0%) were less likely to be treated in urban centers than patients residing in urban areas (99.1%, p<0.001). Rural patients were also less likely to be treated in large town hospitals than large town patients (12% vs. 22%, p=0.0005). Length of stay was not different for rural (5.6 +/− 6.9), large town (5.6 +/− 7.1 day) or urban patients (6.1 +/− 7/0 day) (p=0.3).

Treatment characteristics of the cohort are depicted in TABLE 2. Overall, about 60% of AAAs were repaired by EVAR; 25% in high volume centers; and 50% by vascular surgeons. Rural patients were as likely to receive EVAR and to be treated by vascular surgeons as urban patients. Rural and large town patients were more likely to be treated in a high-volume center than those residing in urban areas; on multivariate analysis, rural residence (OR 1.64, 95% CI 1.34 – 2.01, p<0.0001)) and large town residence (OR 1.96, 95% CI 1.59 – 2.42, p???; TABLE 3) remained the only independent predictors of treatment at a high volume center. Of note, age, co-morbidity score, race, and poverty did not predict treatment in high volume centers.

TABLE 2
Treatment characteristics for intact aneurysm repair
TABLE 3
Multivariate logistic regression of factors predicting treatment at high-volume centers

Overall, 30-day mortality or rehospitalization occurred in 14.9% of the cohort. Event rates were lower for rural patients and large town patients compared with those in urban areas (11.6% vs. 12.8% vs. 16.0%, p <0.05) (TABLE 4). By individual outcomes, rural patients were less likely to die after repair and were less likely to be readmitted, though these differences did not reach statistical significance (TABLE 4). On multivariate analysis, rural residence independently predicted a decreased mortality or readmission (OR 0.70, 95% CI 0.49 – 0.97, p<0.05), as did male gender (OR 0.70, 95% CI 0.54 – 0.89, p<.005; TABLE 5). Other factors significantly predicting increased mortality or readmission included predicted utilization (risk adjustment score), and open repair (TABLE 5). Age 65–74 was associated with decreased events compared with other age groups.

TABLE 4
Primary outcomes after repair of intact AAA
TABLE 5
Multivariate analysis of variables associated with combined 30-day mortality or rehospitalization

DISCUSSION

Our study is the first to describe the national experience for treatment of intact AAA in the endovascular era for patients living in rural areas. We found that most rural patients travel to urban centers for AAA care. Compared with patients living in urban areas, rural patients undergoing AAA repair had equivalent access to EVAR and surgeons with vascular training, better access to high volume centers, and improved outcomes.

Lack of local expertise and the need to refer elsewhere for AAA treatment may have allowed rural patients paradoxically improved access to high-volume centers compared with urban patients This access may in part account for the rural patients’ improved outcomes, as the potential benefit of AAA treatment at high volume centers is well-documented1, 16. Additionally, in the endovascular era an increasing percentage of AAA are being performed at high volume centers; these high volume centers are also more likely to adopt EVAR17. Equivalent access to EVAR for rural patients in our study is consistent with this finding.

Given that care in a high volume center was not an independent predictor of outcome in multivariate analysis suggests that rural patients had better outcomes not solely from access to these high volume centers. Some of the rural patients may have been cared for at high quality low volume centers or by highly qualified specialists who did not practice at high volume centers. Thus, superior outcomes of rural patients represent access to high quality care irrespective of volume. These findings are consistent with other research showing that quality and volume are not perfect surrogates18, and does not quell the controversy over the threshold at which volume improves quality19, 20.

Many barriers prevent regionalization for complex surgical care. Previous research has shown that patients have a preference for local care, and will trade increased mortality for decreased travel distances21. In addition, primary care physicians value not only medical skill of the specialist, but also appointment timeliness, quality communication between the specialist and both the patient and referring physician, and the likelihood that the specialist will return the patient to the primary physician22. Of less importance to the primary physician are hospital affiliation, office location, and patient convenience. Our study suggests that these barriers can be overcome and patients effectively referred from rural areas for AAA care. These barriers, however, may keep patients living in large towns from receiving care in high quality urban centers.

Willingness to refer rural patients to urban settings may reflect a severe shortage of qualified resources at rural hospitals. A recent survey of rural hospital administrators identified that two-thirds were either currently recruiting a general surgeon or expected to within two years23. Additional expenditures required for a viable endovascular program (e.g. specially trained personnel, radiologic imaging, adequate inventory) may prohibit rural hospitals from attracting appropriately trained physicians, even though surgeons have a vital role in the financial viability of these institutions24.

Of potential concern is that urban patients had worse outcomes than rural patients. Urban patients had a higher proportion of minorities and those on Medicaid, which may have impacted outcomes. Other researchers have shown that minority patients are less likely to receive complex surgical care in high-volume hospitals for AAA because they are not referred to such centers25. However, urban patients had significantly worse outcomes even after adjusting for race and Medicaid. It is possible that some urban communities do not have high quality hospitals, and patients would prefer to remain in their own urban area rather than travel to another urban center for care. Alternatively, urban patients are referred for AAA care based on matching hospital affiliation or insurance coverage between the referring physician and specialist, without knowledge or ability of the primary physician to choose a specialist based on expertise and outcomes.

Although rural patients who receive care for AAA do not have disparate outcomes, rural patients may still be less likely to receive operative care. Rural patients must travel two to three times farther than urban patients to be evaluated by surgical specialists6. This geographic isolation may prevent some patients from receiving treatment. Rural patients may also face financial restrictions or cultural factors that prevent access to specialized care. Our dataset did not allow us to test these hypotheses. In addition, once repair is performed, it is unclear if rural patients have adequate long-term follow-up. Although they had fewer re-admissions and superior short-term outcomes in this study, we did not examine outcomes after 30 days. Thus, we cannot evaluate whether these patients received appropriate surveillance after EVAR or had long-term access to sophisticated imaging.

Hospital volume may not be representative when extrapolating from the 5% sample. Our study estimated that 44% of procedures were performed in high-volume hospitals in 2005–2006, slightly higher to that reported in 2002–200417. If hospital volume was over-represented, our findings may have under-estimated the effect of volume on outcomes. However, as rural residence was determined to be a factor predicting care by a high volume center, we would expect the main effect on outcomes to remain the same.

This study has other limitations. Clinical information such as aneurysm dimension or severity of chronic medical conditions was not available. Additionally, all administrative databases may be subject to coding errors, which may over- or under-represent the study variables of interest. However, coding errors are less likely for hospitalizations that result in surgical procedures or require specialist care.2628

In summary, we found that most rural patients travel to urban centers for surgical care of AAA. Despite geographic isolation, patients in rural areas needing treatment for intact AAA have equivalent access to EVAR and vascular surgeons, increased referral to high-volume hospitals, and improved outcomes after repair. Our findings support the need for better criteria to define centers of excellence for aortic care, which would allow improved outcomes for all patients.

Footnotes

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