- Email: [email protected]
Payer Status, Preoperative Surveillance, and Rupture of Abdominal Aortic Aneurysms in the US Medicare Population
Clinical Research Payer Status, Preoperative Surveillance, and Rupture of Abdominal Aortic Aneurysms in the US Medicare Population Matthew W. Mell,1 and Laurence C. Baker,2,3 Stanford, California
Background: To determine the factors contributing to increased rate of ruptured abdominal aortic aneurysms (AAAs) for elderly poor patients. Methods: Medicare claims were analyzed for patients who underwent AAA repair from 2006 to 2009 with preoperative abdominal imaging. Repair for ruptured versus intact AAAs was our primary outcome measure. We used logistic regression to determine the relationship between Medicaid eligibility and the risk of rupture, sequentially adding variables related to patient characteristics, socioeconomic status, receipt of preoperative AAA surveillance, and hospital AAA volume. We then estimated the proportional effect of each factor. Results: No differences in rupture were observed in women based on payer status. Medicaideligible men were more likely to present with ruptured AAA (odds ratio [OR] 2.42, 95% confidence interval [CI] 1.65e3.52). After adjusting for patient and hospital factors, the poor remained at higher risk for rupture (OR 1.5, 95% CI 1.10e2.26). This disparate risk of rupture was more commonly observed in hospitals treating a higher proportion of Medicaid-eligible patients. We estimate that 36% of the observed disparity in rupture for the elderly poor is explained by patient factors, 27% by gaps in surveillance, 9% by hospital factors, and <1% by socioeconomic factors. Conclusions: Incomplete preoperative surveillance is a key contributor to increased rupture of AAA in the elderly poor. Efforts aimed at improving disparities must include consistent access to medical care.
INTRODUCTION Economic disparities exist in the timely repair of abdominal aortic aneurysms (AAAs).1 Medicare patients who are also eligible for Medicaid (dualeligible patients) have an increased likelihood of presenting with a ruptured AAA compared with 1
Division of Vascular Surgery, Stanford University, Stanford, CA.
2
Department of Health Research and Policy, Stanford University, Stanford, CA. 3
National Bureau of Economic Research, Cambridge, MA.
Correspondence to: Matthew W. Mell, MD, Division of Vascular Surgery, Stanford University, 300 Pasteur Drive, suite H3600, Stanford, CA, USA; E-mail: [email protected] Ann Vasc Surg 2014; -: 1–6 http://dx.doi.org/10.1016/j.avsg.2014.02.008 Ó 2014 Elsevier Inc. All rights reserved. Manuscript received: September 30, 2013; manuscript accepted: February 4, 2014; published online: ---.
Medicare patients without dual eligibility. Although research has documented this disparity, no study has investigated the factors that may contribute to these findings. Several factors may influence these observed disparities, including differences in age, race, comorbidity, socioeconomic status, access to preoperative vascular care, or access to hospitals providing treatment for AAA. Hospital-level differences including AAA case volume and difference in payer mix among Medicare patients may also contribute to these disparities. We sought to determine the proportional effect that each of these factors may have contributed to the increased rate of ruptured AAA for Medicare patients with Medicaid eligibility (dual-eligible patients), with particular focus on preoperative surveillance imaging. 1
2 Mell and Baker
METHODS Data Source We extracted data from a 20% sample of fee-forservice Medicare records for individuals undergoing AAA repair between January 1, 2006 and December 31, 2009. Files for hospitalizations (MedPAR, part A), physician claims (part B), and patient demographics (denominator file) were available for review. Patients were identified using International Classification of Diseases, ninth revision, clinical modification (ICD-9-CM) codes for intact AAA (ICD-9-CM codes 441.4 or 441.9) or ruptured AAA (441.3, 441.5) and a procedure code for AAA repair (ICD-9-CM codes 38.34, 38.44, 38.64, 38.92, or 39.71), from the MedPAR (part A) files. Patients were included only if they were at least 67 years old with 2 years of Medicare eligibility to assure the presence of a surveillance window and only with at least a 6-month interval between pertinent diagnostic imaging and repair. Patients with incomplete part A or part B coverage and those without fee-for-service (Medicare Advantage; part C) coverage were excluded. Our treatment group of interest included individuals with eligibility for both Medicare and Medicaid coverage (dual-eligible patients). Our control group included all other patients who were eligible for only Medicare coverage. Patients with dual eligibility are some of the most economically disadvantaged individuals who are covered under the Medicare program. To be dual-eligible, patients must be able to demonstrate a yearly income <100% of the Federal Poverty Level, and total financial resources <3 times the Supplemental Security Income Limit. In 2008, the Federal Poverty Level was $10,400 for individuals and $14,000 for couples, and the Supplemental Security Income Limit was $2,000 for individuals and $9,000 for couples. For our cohort, we followed back patients for up to 5 years to collect information about preoperative imaging, as previously described.1,2 Diagnostic images of the abdomen or retroperitoneum included ultrasound examinations (CPT codes 76,700, 76,705, 76,770, 76,775, G0389, 93,975, 93,976, 93,978, 93,979), computerized tomographic (CT) scans (codes 72,191, 72,192, 72,193, 72,194, 74,150, 74,160, 74,170, 74,175, 74,176, 74,177, 74,178, 74,261, 74,262, 74,263, 75,635), or magnetic resonance imaging (MRI; codes 74,181, 74,182, 74,183, 74,184, 74,185, 72,195, 72,196, 72,197, 72,198). Multiple imaging codes on the same day for the same imaging modality were considered one examination to avoid double counting.
Annals of Vascular Surgery
Surveillance imaging examinations were defined as those performed after the first recorded examination and prior to 7 days before the index admission (the admission for which the AAA was repaired). We chose 7 days before the index admission to avoid counting scans performed for preoperative planning as surveillance images. As AAA diameter was not available, we postulated that most AAA were repaired at diameters >4.5 cm. Based on the Society of Vascular Surgery recommendations for surveillance imaging of 4.5e5.4 cm AAA3 and allowing for an additional 6-month grace period between final surveillance image and repair, we defined incomplete preoperative AAA management as no imaging examination within 1 year of the repair or no imaging for more than a 2-year time span. Statistical Analysis We compared the risk-adjusted rates of rupture before AAA repair for dual-eligible patients compared with patients having traditional fee-forservice Medicare using logistic regression to determine the relationship between Medicaid eligibility and the risk of rupture. We then repeated the analysis by sequentially adding categories of variables related to patient characteristics, socioeconomic status, receipt of preoperative AAA surveillance, and yearly hospital AAA repair volume, determined by quintiles. The contribution of each category to the difference between Medicaid eligibility and Medicare-only subjects was then estimated by calculating the proportional difference in predicted probability (pp) for rupture for each model compared with the base model, holding all other variables constant: proportion of disparity explained ¼ (ppnew model ppbase model)/ppbase model. Patient characteristics, including age, sex, race, and comorbidities, using methodology described by Elixhauser et al.,4 a conventional technique of adjusting for underlying medical conditions using administrative data. Socioeconomic status was estimated using zip codeelevel variables based on the 2000 US Census, modified from methods described by Birkmeyer et al.5 The composite measure included median household income, median housing value, proportion of housing units with rental, interest, or dividend income, proportion of adults completing high school education, proportion of adults completing college education, and proportion of residents employed in high-level (management, professional, or related) occupations. We observed a significant interaction between dual eligibility and sex (P < 0.001) and so results were stratified by sex.
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Factors contributing to increased rate of AAA rupture 3
Table I. Patient characteristics Variable
Male, % Age, mean (years) Congestive heart failure Chronic lung disease Vascular disease Chronic renal failure Diabetes Uncomplicated Complicated
Dual-eligible Medicare patients patients P value
53.7 77.8 6.4 42.2 33.2 14.1
76.8 78.0 4.7 29.3 35.7 11.1
<0.0001 0.35 0.04 <0.0001 0.19 0.02
15.0 0.7
14.0 0.7
0.50 0.95
In a separate analysis, we stratified hospitals into quintiles by the proportion of dual-eligible patients treated for AAA to determine if the rate of rupture and the variation in rupture rates were different for the cohort in relation to the percentage of dual-eligible patients treated. The lowest quintile had no dual-eligible patients and was excluded from the stratified analysis. We then used logistic regression models to estimate the adjusted risk of surveillance gaps and the adjusted risk of rupture before repair. Differences with two-tailed P values of <0.05 were considered significant. Statistical analyses were performed using SAS version 9.1.3 (SAS Institute, Cary, NC) and Stata version 11.2 (StataCorp, College Station, TX).
RESULTS A total of 9,063 patients underwent repair for AAA with at least a 6-month interval between first imaging and surgical repair. Of these, 689 (7.6%) had dual eligibility. Women constituted 24.9% of the entire cohort and 46.3% of patients with dual eligibility. Characteristics of the dual-eligible and Medicare-only groups are listed in Table I. No difference was noted in age (77.8 ± 6.2 vs 78.0 ± 5.9, P ¼ 0.35). By race, fewer Caucasian patients had dual eligibility (6.7% vs 24.5%, P < 0.001). A greater proportion of women were dual eligible. Dual-eligible patients were more likely to have congestive heart failure, pulmonary disease, and renal failure, and less likely to be treated in a hospital with high yearly volumes for AAA repair (55% vs 59%, P ¼ 0.03). Dual-eligible patients more frequently had incomplete preoperative AAA surveillance before repair (18.7% vs 13.2%, P < 0.001). Incomplete surveillance remained 40% more likely for dualeligible patients after adjusting for age, sex, race,
Table II. Odds of rupture for dual-eligible relative to Medicare-only men Proportion of disparity P value explained,%
Model
OR (95% CI)
Unadjusted Adjusted for Patient factors Complete surveillance Hospital factors Socioeconomic factors
2.41 (1.65e3.52) <0.001 d d 2.36 (1.54e3.61) <0.001 36 2.27 (1.46e3.53) <0.001 27 2.21 (1.42e3.45) <0.001 9 2.16 (1.37e3.39) 0.001 <1
Area under the receiver operating characteristic curve of the final model ¼ 0.84.
comorbidity, socioeconomic status, hospital teaching status, and year of repair (adjusted odds ratio [OR] 1.40, 95% confidence interval [CI] 1.12e 1.76, P ¼ 0.004). The overall risk of rupture before repair was 4.7%. We observed a significant interaction between dual eligibility and sex (P < 0.001). Stratified by sex, there was a significant sex difference in an unadjusted analysis in that women with dual eligibility had no increased risk in rupture (OR 1.06; 95% CI 0.66e1.72, P ¼ 0.79), whereas dualeligible men had a 141% higher likelihood of rupture before repair (OR 2.41; 95% CI 1.65e3.52, P < 0.001) compared with Medicare-only men. After controlling for patient factors, dual-eligible men were still 136% more likely to rupture before repair (OR 2.36; 95% CI 1.54e3.61, P < 0.001). After adjusting for differences in preoperative surveillance, dual-eligible patients continued to be 127% more likely to rupture (OR 2.27; 95% CI 1.46e3.53, P < 0.001). Socioeconomic and measured hospital AAA repair volume had only a modest effect on rupture risk (Table II). We estimate that 36% of the observed disparity in rupture for those with dual eligibility is explained by patient factors, 27% by gaps in surveillance, 9% by hospital factors, and <1% by socioeconomic factors. When hospitals were stratified by the proportion of those treated with dual eligibility, significant variation in the proportion of dual-eligible patients treated was observed, from 0% in the lowest quintile to 23.5% in the highest quintile (Fig. 1). The lowest quintile was excluded from the stratified analysis. The adjusted risk for surveillance gaps increased proportionally as the proportion of treated dual-eligible patients increased, for both dualeligible (P < 0.001) and Medicare-only patients (P < 0.001; Fig. 2). The rate of increase appeared
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Fig. 1. Hospitals stratified by proportion of dual-eligible patients treated (2006e2009). Fig. 3. Risk-adjusted rates of rupture before repair for dual-eligible and Medicare-only patients in hospitals stratified by the proportion of dual-eligible AAAs treated (2006e2009).
Fig. 2. Risk-adjusted rates of preoperative surveillance gaps for dual-eligible and Medicare-only patients in hospitals stratified by the proportion of dual-eligible AAAs treated (2006e2009).
to be similar for each group. Differences in risk of rupture increased between dual-eligible and Medicare-only patients as the proportion of dualeligible patients treated increased (Fig. 3). In the hospitals treating the lowest proportion of dual-eligible patients, there was no difference in risk-adjusted rupture (0.5% vs 0.2%, P ¼ 0.37), whereas dualeligible patients from hospitals treating the highest proportion of Medicaid patients had higher adjusted risk of rupture (6.5% vs 2.8%, P ¼ 0.03). The proportional increase in rupture before repair was approximately the same for both groups across quintiles.
DISCUSSION This study describes the factors associated with an increased rupture of previously diagnosed AAA for
Medicare patients with eligibility for Medicaid insurance. We have previously shown that within the fee-for-service Medicare population those with eligibility for Medicaid are more likely to rupture previously diagnosed AAA.1 These observations are consistent with other studies showing disparities in care for Medicaid patients for access to new technology,6,7 high-volume hospitals for complex surgery,8 treatment of early-stage lung cancer,9 and mortality after AAA repair10 or other major surgical operations.11 A variety of factors have been postulated to explain these observed disparities, including decreased access to primary or specialty care, inadequate patient education or knowledge, or language barriers. Cultural differences regarding preventative care may also influence health-seeking behavior.9 We estimate that for men, gaps in preoperative surveillance accounts for over one-fourth of the difference in rupture risk between dual-eligible and fee-for-service Medicare patients. Efforts to improve surveillance imaging is an actionable item and can be done at the patient level including providing specific educational material regarding the importance of ongoing surveillance, the natural history of AAA, and the improved outcomes with surveillance and surgical repair when indicated. A diagnosis of AAA may also provide a portal to cardiovascular risk reduction efforts including initiation of statin therapy, which has been shown to reduce mortality for patients with small AAA.12 We found that the absolute difference in rupture risk between dual-eligible and Medicare patients appeared to increase at hospitals serving a larger proportion of dual-eligible patients, suggesting that
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discrimination may contribute to disparate outcomes. To address this, patient-level efforts can and should be coupled with physician-level and hospital-level efforts to overcome barriers to preventative AAA care. This may include physician education regarding the value of ongoing surveillance of AAA and implementation of systems to accurately identify and follow patients with AAA. When available, the electronic medical record (EMR) can be leveraged for such purposes. Studies from the Veterans Affairs Health Care system have demonstrated effective use of the EMR for such purposes.13 The difference in outcomes based on insurance status for men was not observed for women. This finding may be explained by differences in sexrelated attitudes regarding medical care, preventative care, or the role of surgery for prevention of rupture among the poor. Family structure or preexisting biases toward health care may have contributed to an increased likelihood of dual-eligible women receiving repair before rupture compared with men. Alternatively, it is possible that our study was underpowered to detect a difference for women. For men, 3.9% of Medicare patients and 8.9% of dual-eligible patients presented with rupture, for women the rates were 6.2% and 6.6%, and for the entire cohort the rates were 4.4% and 7.8%, respectively. If the effect of poverty on rupture were similar for men and women, the required sample size for women is estimated to be 1,670e3,500 subjects. There are several noteworthy limitations to this study. Our model did not explain approximately one-fourth of the disparity between groups. This remainder may be because of either unmeasured factors or limitations of the measured factors. Examples of the former may include difference in access to primary or specialty care, aneurysm size, or differing attitudes toward receiving preventative care. Examples of the latter include lack of precision for measuring the components of socioeconomic status, which was limited to zip codeelevel (and not patient level) data and may not accurately estimate the effect of an individual’s education, income, or wealth on the likelihood of rupture. As with all retrospective observational studies, selection bias may be present as potential confounding variables may not be available. Errors in coding may be present, although they are less likely for conditions such as AAA that require surgery.14e16 It is possible that some patients who qualified for dual eligibility were not dual eligible at the time of repair or their eligibility status changed during the study
Factors contributing to increased rate of AAA rupture 5
period. Important clinical variables such as aneurysm size or growth rates, smoking status, and severity of comorbidities may have contributed to the risk of rupture but were not available. Finally, as the Medicare population accounts for w70% of all AAA repairs,17 our findings may not be generalizable to non-Medicare populations. We believe, however, that these limitations do not detract from our primary findings. In conclusion, incomplete preoperative surveillance is a significant modifiable contributor to increased rupture of AAA in the elderly poor. Efforts aimed at improving disparities should include consistent access to medical care. REFERENCES 1. Mell MW, Baker LC, Dalman RL, et al. Gaps in pre-operative surveillance and rupture of abdominal aortic aneurysms among Medicare beneficiaries. J Vasc Surg 2014;59:583e8. 2. Mell MW, Hlatky MA, Shreibati JB, et al. Late diagnosis of abdominal aortic aneurysms substantiates underutilization of abdominal aortic aneurysm screening for Medicare beneficiaries. J Vasc Surg 2013;57:1519e23. 1523.e1. 3. Chaikof EL, Brewster DC, Dalman RL, et al. The care of patients with an abdominal aortic aneurysm: the Society for Vascular Surgery practice guidelines. J Vasc Surg 2009; 50(4 Suppl):S2e49. 4. Elixhauser A, Steiner C, Harris DR, et al. Comorbidity measures for use with administrative data. Med Care 1998; 36:8e27. 5. Birkmeyer NJ, Gu N, Baser O, et al. Socioeconomic status and surgical mortality in the elderly. Med Care 2008;46: 893e9. 6. Greenstein AJ, Romanoff AM, Moskowitz AJ, et al. Payer status and access to laparoscopic subtotal colectomy for ulcerative colitis. Dis Colon Rectum 2013;56:1062e7. 7. Osborne NH, Mathur AK, Upchurch GR Jr, et al. Understanding the racial disparity in the receipt of endovascular abdominal aortic aneurysm repair. Arch Surg 2010;145: 1105e8. 8. Liu JH, Zingmond DS, McGory ML, et al. Disparities in the utilization of high-volume hospitals for complex surgery. JAMA 2006;296:1973e80. 9. Groth SS, Al-Refaie WB, Zhong W, et al. Effect of insurance status on the surgical treatment of early-stage non-small cell lung cancer. Ann Thorac Surg 2013;95:1221e6. 10. Osborne NH, Upchurch GR Jr, Mathur AK, et al. Explaining racial disparities in mortality after abdominal aortic aneurysm repair. J Vasc Surg 2009;50:709e13. 11. LaPar DJ, Bhamidipati CM, Mery CM, et al. Primary payer status affects mortality for major surgical operations. Ann Surg 2010;252:544e50. discussion 550e1. 12. Twine CP, Williams IM. Systematic review and metaanalysis of the effects of statin therapy on abdominal aortic aneurysms. Br J Surg 2011;98:346e53. 13. Chun KC, Teng KY, Van Spyk EN, et al. Outcomes of an abdominal aortic aneurysm screening program. J Vasc Surg 2013;57:376e81. 14. Kiyota Y, Schneeweiss S, Glynn RJ, et al. Accuracy of Medicare claims-based diagnosis of acute myocardial
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infarction: estimating positive predictive value on the basis of review of hospital records. Am Heart J 2004;148:99e104. 15. Quan H, Parsons GA, Ghali WA. Validity of procedure codes in International Classification of Diseases, 9th revision, clinical modification administrative data. Med Care 2004;42: 801e9.
Annals of Vascular Surgery
16. Wilchesky M, Tamblyn RM, Huang A. Validation of diagnostic codes within medical services claims. J Clin Epidemiol 2004;57:131e41. 17. Birkmeyer JD, Siewers AE, Finlayson EV, et al. Hospital volume and surgical mortality in the United States. N Engl J Med 2002;346:1128e37.
Background: To determine the factors contributing to increased rate of ruptured abdominal aortic aneurysms (AAAs) for elderly poor patients. Methods: Medicare claims were analyzed for patients who underwent AAA repair from 2006 to 2009 with preoperative abdominal imaging. Repair for ruptured versus intact AAAs was our primary outcome measure. We used logistic regression to determine the relationship between Medicaid eligibility and the risk of rupture, sequentially adding variables related to patient characteristics, socioeconomic status, receipt of preoperative AAA surveillance, and hospital AAA volume. We then estimated the proportional effect of each factor. Results: No differences in rupture were observed in women based on payer status. Medicaideligible men were more likely to present with ruptured AAA (odds ratio [OR] 2.42, 95% confidence interval [CI] 1.65e3.52). After adjusting for patient and hospital factors, the poor remained at higher risk for rupture (OR 1.5, 95% CI 1.10e2.26). This disparate risk of rupture was more commonly observed in hospitals treating a higher proportion of Medicaid-eligible patients. We estimate that 36% of the observed disparity in rupture for the elderly poor is explained by patient factors, 27% by gaps in surveillance, 9% by hospital factors, and <1% by socioeconomic factors. Conclusions: Incomplete preoperative surveillance is a key contributor to increased rupture of AAA in the elderly poor. Efforts aimed at improving disparities must include consistent access to medical care.
INTRODUCTION Economic disparities exist in the timely repair of abdominal aortic aneurysms (AAAs).1 Medicare patients who are also eligible for Medicaid (dualeligible patients) have an increased likelihood of presenting with a ruptured AAA compared with 1
Division of Vascular Surgery, Stanford University, Stanford, CA.
2
Department of Health Research and Policy, Stanford University, Stanford, CA. 3
National Bureau of Economic Research, Cambridge, MA.
Correspondence to: Matthew W. Mell, MD, Division of Vascular Surgery, Stanford University, 300 Pasteur Drive, suite H3600, Stanford, CA, USA; E-mail: [email protected] Ann Vasc Surg 2014; -: 1–6 http://dx.doi.org/10.1016/j.avsg.2014.02.008 Ó 2014 Elsevier Inc. All rights reserved. Manuscript received: September 30, 2013; manuscript accepted: February 4, 2014; published online: ---.
Medicare patients without dual eligibility. Although research has documented this disparity, no study has investigated the factors that may contribute to these findings. Several factors may influence these observed disparities, including differences in age, race, comorbidity, socioeconomic status, access to preoperative vascular care, or access to hospitals providing treatment for AAA. Hospital-level differences including AAA case volume and difference in payer mix among Medicare patients may also contribute to these disparities. We sought to determine the proportional effect that each of these factors may have contributed to the increased rate of ruptured AAA for Medicare patients with Medicaid eligibility (dual-eligible patients), with particular focus on preoperative surveillance imaging. 1
2 Mell and Baker
METHODS Data Source We extracted data from a 20% sample of fee-forservice Medicare records for individuals undergoing AAA repair between January 1, 2006 and December 31, 2009. Files for hospitalizations (MedPAR, part A), physician claims (part B), and patient demographics (denominator file) were available for review. Patients were identified using International Classification of Diseases, ninth revision, clinical modification (ICD-9-CM) codes for intact AAA (ICD-9-CM codes 441.4 or 441.9) or ruptured AAA (441.3, 441.5) and a procedure code for AAA repair (ICD-9-CM codes 38.34, 38.44, 38.64, 38.92, or 39.71), from the MedPAR (part A) files. Patients were included only if they were at least 67 years old with 2 years of Medicare eligibility to assure the presence of a surveillance window and only with at least a 6-month interval between pertinent diagnostic imaging and repair. Patients with incomplete part A or part B coverage and those without fee-for-service (Medicare Advantage; part C) coverage were excluded. Our treatment group of interest included individuals with eligibility for both Medicare and Medicaid coverage (dual-eligible patients). Our control group included all other patients who were eligible for only Medicare coverage. Patients with dual eligibility are some of the most economically disadvantaged individuals who are covered under the Medicare program. To be dual-eligible, patients must be able to demonstrate a yearly income <100% of the Federal Poverty Level, and total financial resources <3 times the Supplemental Security Income Limit. In 2008, the Federal Poverty Level was $10,400 for individuals and $14,000 for couples, and the Supplemental Security Income Limit was $2,000 for individuals and $9,000 for couples. For our cohort, we followed back patients for up to 5 years to collect information about preoperative imaging, as previously described.1,2 Diagnostic images of the abdomen or retroperitoneum included ultrasound examinations (CPT codes 76,700, 76,705, 76,770, 76,775, G0389, 93,975, 93,976, 93,978, 93,979), computerized tomographic (CT) scans (codes 72,191, 72,192, 72,193, 72,194, 74,150, 74,160, 74,170, 74,175, 74,176, 74,177, 74,178, 74,261, 74,262, 74,263, 75,635), or magnetic resonance imaging (MRI; codes 74,181, 74,182, 74,183, 74,184, 74,185, 72,195, 72,196, 72,197, 72,198). Multiple imaging codes on the same day for the same imaging modality were considered one examination to avoid double counting.
Annals of Vascular Surgery
Surveillance imaging examinations were defined as those performed after the first recorded examination and prior to 7 days before the index admission (the admission for which the AAA was repaired). We chose 7 days before the index admission to avoid counting scans performed for preoperative planning as surveillance images. As AAA diameter was not available, we postulated that most AAA were repaired at diameters >4.5 cm. Based on the Society of Vascular Surgery recommendations for surveillance imaging of 4.5e5.4 cm AAA3 and allowing for an additional 6-month grace period between final surveillance image and repair, we defined incomplete preoperative AAA management as no imaging examination within 1 year of the repair or no imaging for more than a 2-year time span. Statistical Analysis We compared the risk-adjusted rates of rupture before AAA repair for dual-eligible patients compared with patients having traditional fee-forservice Medicare using logistic regression to determine the relationship between Medicaid eligibility and the risk of rupture. We then repeated the analysis by sequentially adding categories of variables related to patient characteristics, socioeconomic status, receipt of preoperative AAA surveillance, and yearly hospital AAA repair volume, determined by quintiles. The contribution of each category to the difference between Medicaid eligibility and Medicare-only subjects was then estimated by calculating the proportional difference in predicted probability (pp) for rupture for each model compared with the base model, holding all other variables constant: proportion of disparity explained ¼ (ppnew model ppbase model)/ppbase model. Patient characteristics, including age, sex, race, and comorbidities, using methodology described by Elixhauser et al.,4 a conventional technique of adjusting for underlying medical conditions using administrative data. Socioeconomic status was estimated using zip codeelevel variables based on the 2000 US Census, modified from methods described by Birkmeyer et al.5 The composite measure included median household income, median housing value, proportion of housing units with rental, interest, or dividend income, proportion of adults completing high school education, proportion of adults completing college education, and proportion of residents employed in high-level (management, professional, or related) occupations. We observed a significant interaction between dual eligibility and sex (P < 0.001) and so results were stratified by sex.
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Factors contributing to increased rate of AAA rupture 3
Table I. Patient characteristics Variable
Male, % Age, mean (years) Congestive heart failure Chronic lung disease Vascular disease Chronic renal failure Diabetes Uncomplicated Complicated
Dual-eligible Medicare patients patients P value
53.7 77.8 6.4 42.2 33.2 14.1
76.8 78.0 4.7 29.3 35.7 11.1
<0.0001 0.35 0.04 <0.0001 0.19 0.02
15.0 0.7
14.0 0.7
0.50 0.95
In a separate analysis, we stratified hospitals into quintiles by the proportion of dual-eligible patients treated for AAA to determine if the rate of rupture and the variation in rupture rates were different for the cohort in relation to the percentage of dual-eligible patients treated. The lowest quintile had no dual-eligible patients and was excluded from the stratified analysis. We then used logistic regression models to estimate the adjusted risk of surveillance gaps and the adjusted risk of rupture before repair. Differences with two-tailed P values of <0.05 were considered significant. Statistical analyses were performed using SAS version 9.1.3 (SAS Institute, Cary, NC) and Stata version 11.2 (StataCorp, College Station, TX).
RESULTS A total of 9,063 patients underwent repair for AAA with at least a 6-month interval between first imaging and surgical repair. Of these, 689 (7.6%) had dual eligibility. Women constituted 24.9% of the entire cohort and 46.3% of patients with dual eligibility. Characteristics of the dual-eligible and Medicare-only groups are listed in Table I. No difference was noted in age (77.8 ± 6.2 vs 78.0 ± 5.9, P ¼ 0.35). By race, fewer Caucasian patients had dual eligibility (6.7% vs 24.5%, P < 0.001). A greater proportion of women were dual eligible. Dual-eligible patients were more likely to have congestive heart failure, pulmonary disease, and renal failure, and less likely to be treated in a hospital with high yearly volumes for AAA repair (55% vs 59%, P ¼ 0.03). Dual-eligible patients more frequently had incomplete preoperative AAA surveillance before repair (18.7% vs 13.2%, P < 0.001). Incomplete surveillance remained 40% more likely for dualeligible patients after adjusting for age, sex, race,
Table II. Odds of rupture for dual-eligible relative to Medicare-only men Proportion of disparity P value explained,%
Model
OR (95% CI)
Unadjusted Adjusted for Patient factors Complete surveillance Hospital factors Socioeconomic factors
2.41 (1.65e3.52) <0.001 d d 2.36 (1.54e3.61) <0.001 36 2.27 (1.46e3.53) <0.001 27 2.21 (1.42e3.45) <0.001 9 2.16 (1.37e3.39) 0.001 <1
Area under the receiver operating characteristic curve of the final model ¼ 0.84.
comorbidity, socioeconomic status, hospital teaching status, and year of repair (adjusted odds ratio [OR] 1.40, 95% confidence interval [CI] 1.12e 1.76, P ¼ 0.004). The overall risk of rupture before repair was 4.7%. We observed a significant interaction between dual eligibility and sex (P < 0.001). Stratified by sex, there was a significant sex difference in an unadjusted analysis in that women with dual eligibility had no increased risk in rupture (OR 1.06; 95% CI 0.66e1.72, P ¼ 0.79), whereas dualeligible men had a 141% higher likelihood of rupture before repair (OR 2.41; 95% CI 1.65e3.52, P < 0.001) compared with Medicare-only men. After controlling for patient factors, dual-eligible men were still 136% more likely to rupture before repair (OR 2.36; 95% CI 1.54e3.61, P < 0.001). After adjusting for differences in preoperative surveillance, dual-eligible patients continued to be 127% more likely to rupture (OR 2.27; 95% CI 1.46e3.53, P < 0.001). Socioeconomic and measured hospital AAA repair volume had only a modest effect on rupture risk (Table II). We estimate that 36% of the observed disparity in rupture for those with dual eligibility is explained by patient factors, 27% by gaps in surveillance, 9% by hospital factors, and <1% by socioeconomic factors. When hospitals were stratified by the proportion of those treated with dual eligibility, significant variation in the proportion of dual-eligible patients treated was observed, from 0% in the lowest quintile to 23.5% in the highest quintile (Fig. 1). The lowest quintile was excluded from the stratified analysis. The adjusted risk for surveillance gaps increased proportionally as the proportion of treated dual-eligible patients increased, for both dualeligible (P < 0.001) and Medicare-only patients (P < 0.001; Fig. 2). The rate of increase appeared
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Fig. 1. Hospitals stratified by proportion of dual-eligible patients treated (2006e2009). Fig. 3. Risk-adjusted rates of rupture before repair for dual-eligible and Medicare-only patients in hospitals stratified by the proportion of dual-eligible AAAs treated (2006e2009).
Fig. 2. Risk-adjusted rates of preoperative surveillance gaps for dual-eligible and Medicare-only patients in hospitals stratified by the proportion of dual-eligible AAAs treated (2006e2009).
to be similar for each group. Differences in risk of rupture increased between dual-eligible and Medicare-only patients as the proportion of dualeligible patients treated increased (Fig. 3). In the hospitals treating the lowest proportion of dual-eligible patients, there was no difference in risk-adjusted rupture (0.5% vs 0.2%, P ¼ 0.37), whereas dualeligible patients from hospitals treating the highest proportion of Medicaid patients had higher adjusted risk of rupture (6.5% vs 2.8%, P ¼ 0.03). The proportional increase in rupture before repair was approximately the same for both groups across quintiles.
DISCUSSION This study describes the factors associated with an increased rupture of previously diagnosed AAA for
Medicare patients with eligibility for Medicaid insurance. We have previously shown that within the fee-for-service Medicare population those with eligibility for Medicaid are more likely to rupture previously diagnosed AAA.1 These observations are consistent with other studies showing disparities in care for Medicaid patients for access to new technology,6,7 high-volume hospitals for complex surgery,8 treatment of early-stage lung cancer,9 and mortality after AAA repair10 or other major surgical operations.11 A variety of factors have been postulated to explain these observed disparities, including decreased access to primary or specialty care, inadequate patient education or knowledge, or language barriers. Cultural differences regarding preventative care may also influence health-seeking behavior.9 We estimate that for men, gaps in preoperative surveillance accounts for over one-fourth of the difference in rupture risk between dual-eligible and fee-for-service Medicare patients. Efforts to improve surveillance imaging is an actionable item and can be done at the patient level including providing specific educational material regarding the importance of ongoing surveillance, the natural history of AAA, and the improved outcomes with surveillance and surgical repair when indicated. A diagnosis of AAA may also provide a portal to cardiovascular risk reduction efforts including initiation of statin therapy, which has been shown to reduce mortality for patients with small AAA.12 We found that the absolute difference in rupture risk between dual-eligible and Medicare patients appeared to increase at hospitals serving a larger proportion of dual-eligible patients, suggesting that
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discrimination may contribute to disparate outcomes. To address this, patient-level efforts can and should be coupled with physician-level and hospital-level efforts to overcome barriers to preventative AAA care. This may include physician education regarding the value of ongoing surveillance of AAA and implementation of systems to accurately identify and follow patients with AAA. When available, the electronic medical record (EMR) can be leveraged for such purposes. Studies from the Veterans Affairs Health Care system have demonstrated effective use of the EMR for such purposes.13 The difference in outcomes based on insurance status for men was not observed for women. This finding may be explained by differences in sexrelated attitudes regarding medical care, preventative care, or the role of surgery for prevention of rupture among the poor. Family structure or preexisting biases toward health care may have contributed to an increased likelihood of dual-eligible women receiving repair before rupture compared with men. Alternatively, it is possible that our study was underpowered to detect a difference for women. For men, 3.9% of Medicare patients and 8.9% of dual-eligible patients presented with rupture, for women the rates were 6.2% and 6.6%, and for the entire cohort the rates were 4.4% and 7.8%, respectively. If the effect of poverty on rupture were similar for men and women, the required sample size for women is estimated to be 1,670e3,500 subjects. There are several noteworthy limitations to this study. Our model did not explain approximately one-fourth of the disparity between groups. This remainder may be because of either unmeasured factors or limitations of the measured factors. Examples of the former may include difference in access to primary or specialty care, aneurysm size, or differing attitudes toward receiving preventative care. Examples of the latter include lack of precision for measuring the components of socioeconomic status, which was limited to zip codeelevel (and not patient level) data and may not accurately estimate the effect of an individual’s education, income, or wealth on the likelihood of rupture. As with all retrospective observational studies, selection bias may be present as potential confounding variables may not be available. Errors in coding may be present, although they are less likely for conditions such as AAA that require surgery.14e16 It is possible that some patients who qualified for dual eligibility were not dual eligible at the time of repair or their eligibility status changed during the study
Factors contributing to increased rate of AAA rupture 5
period. Important clinical variables such as aneurysm size or growth rates, smoking status, and severity of comorbidities may have contributed to the risk of rupture but were not available. Finally, as the Medicare population accounts for w70% of all AAA repairs,17 our findings may not be generalizable to non-Medicare populations. We believe, however, that these limitations do not detract from our primary findings. In conclusion, incomplete preoperative surveillance is a significant modifiable contributor to increased rupture of AAA in the elderly poor. Efforts aimed at improving disparities should include consistent access to medical care. REFERENCES 1. Mell MW, Baker LC, Dalman RL, et al. Gaps in pre-operative surveillance and rupture of abdominal aortic aneurysms among Medicare beneficiaries. J Vasc Surg 2014;59:583e8. 2. Mell MW, Hlatky MA, Shreibati JB, et al. Late diagnosis of abdominal aortic aneurysms substantiates underutilization of abdominal aortic aneurysm screening for Medicare beneficiaries. J Vasc Surg 2013;57:1519e23. 1523.e1. 3. Chaikof EL, Brewster DC, Dalman RL, et al. The care of patients with an abdominal aortic aneurysm: the Society for Vascular Surgery practice guidelines. J Vasc Surg 2009; 50(4 Suppl):S2e49. 4. Elixhauser A, Steiner C, Harris DR, et al. Comorbidity measures for use with administrative data. Med Care 1998; 36:8e27. 5. Birkmeyer NJ, Gu N, Baser O, et al. Socioeconomic status and surgical mortality in the elderly. Med Care 2008;46: 893e9. 6. Greenstein AJ, Romanoff AM, Moskowitz AJ, et al. Payer status and access to laparoscopic subtotal colectomy for ulcerative colitis. Dis Colon Rectum 2013;56:1062e7. 7. Osborne NH, Mathur AK, Upchurch GR Jr, et al. Understanding the racial disparity in the receipt of endovascular abdominal aortic aneurysm repair. Arch Surg 2010;145: 1105e8. 8. Liu JH, Zingmond DS, McGory ML, et al. Disparities in the utilization of high-volume hospitals for complex surgery. JAMA 2006;296:1973e80. 9. Groth SS, Al-Refaie WB, Zhong W, et al. Effect of insurance status on the surgical treatment of early-stage non-small cell lung cancer. Ann Thorac Surg 2013;95:1221e6. 10. Osborne NH, Upchurch GR Jr, Mathur AK, et al. Explaining racial disparities in mortality after abdominal aortic aneurysm repair. J Vasc Surg 2009;50:709e13. 11. LaPar DJ, Bhamidipati CM, Mery CM, et al. Primary payer status affects mortality for major surgical operations. Ann Surg 2010;252:544e50. discussion 550e1. 12. Twine CP, Williams IM. Systematic review and metaanalysis of the effects of statin therapy on abdominal aortic aneurysms. Br J Surg 2011;98:346e53. 13. Chun KC, Teng KY, Van Spyk EN, et al. Outcomes of an abdominal aortic aneurysm screening program. J Vasc Surg 2013;57:376e81. 14. Kiyota Y, Schneeweiss S, Glynn RJ, et al. Accuracy of Medicare claims-based diagnosis of acute myocardial
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