Long-Term Postplacement Cost Comparison of AneuRx and Zenith Endografts

Article Outline

• Abstract
• Introduction
• Methods
  • Statistical Analysis
• Results
  • Postplacement costs
• Discussion
• Conclusions
• References
• Copyright

Long-term postplacement costs increase the global cost of endovascular aneurysm repair (EVAR) by 44%. Secondary procedures and endoleaks significantly increase long-term expense. This study evaluates device-specific long-term postplacement costs using two different endografts. AneuRx and Zenith endografts were used to treat 250 patients with abdominal aortic aneurysms between December 1998 and June 2006 at a single institution. A relative value unit-based hospital cost accounting system was used to calculate both direct and indirect hospital departmental costs. Institutional overhead expenses, costs of professional services, and outpatient visits were also included in cost determinations. All costs were valued in 2006 dollars. To examine long-term costs, patients with <1 year follow-up were excluded. The initial 50 EVAR patients between December 1995 and 1998 were also excluded, to limit the effect of the learning curve on postplacement cost. The cumulative 5-year postplacement costs per patient were $12,465 (AneuRx) and $10,606 (Zenith, p = 0.22). Mean durations of follow-up were 38.5 ± 5.2 months (AneuRx) and 32.8 ± 3.8 months (Zenith, p = 0.12). For both devices, the largest cost components were secondary procedures (59.5% AneuRx vs. 56.4% Zenith) and radiologic studies (29.2% AneuRx vs. 34.9% Zenith). Freedom from secondary procedures (80% vs. 51%, p < 0.05) and endoleaks (83% vs. 58%, p = 0.05) was higher in patients treated with Zenith vs. AneuRx endografts, respectively. There was a reduction in secondary procedures and endoleaks in patients treated with Zenith compared to AneuRx. The corresponding 15% reduction in cost, however, was not statistically significant. Additional device-related cost reductions may be possible through improvements in device and technique and alterations in surveillance imaging.

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Introduction 

It has been well established that despite lower perioperative morbidity, shorter hospital length of stay, and decreased procedural time, the initial hospital cost of endovascular abdominal aortic aneurysm repair (EVAR) exceeds that of open repair.¹, ², ³, ⁴, ⁵ This is primarily due to a high endograft device cost, which comprises >50% of total initial placement expense.¹ In addition to the initial expense of EVAR, there are significant long-term postplacement costs. Secondary procedures and radiologic studies account for 89.9% of postplacement costs.⁶ Furthermore, the patient subsets with secondary procedures or endoleaks generate disproportionate shares of postplacement expense. At 5 years, postplacement costs increase the global cost of EVAR by 44%.⁶

While endograft device selection may influence certain EVAR outcomes,⁷, ⁸, ⁹, ¹⁰ the effect of endograft device upon postplacement costs has not been previously evaluated. This study compares device-specific long-term postplacement costs and evaluates differences in postplacement cost generators. Cost considerations are relevant in today's financially strained health-care system, and differences in device-specific postplacement costs may be another selection consideration.

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Methods 

AneuRx (Medtronic/AVE, Santa Rosa, CA) and Zenith (Cook, Bloomington, IN) endografts were used to complete 250 EVARs at the Ochsner Clinic Foundation Hospital (OCF) between December 1998 and June 2006. Our prospectively maintained endograft database was retrospectively reviewed to identify patient demographics, device type, postplacement radiologic studies, secondary procedures, outpatient visits, laboratory studies, and related hospital readmissions. Additional data were obtained through retrospective medical record review.

Our long-term postplacement costs for EVAR were previously placed into a financial database and the results reported.⁶ Device-specific postplacement costs were obtained through further subset analysis of these data. To evaluate the long-term postplacement costs, patients with <1 year of follow-up at OCF were excluded. To limit the effects of the early learning curve on cost, our initial 50 EVAR patients from December 1995 through 1998 were also excluded. Direct patient care postplacement costs were established through our institutional cost accounting system (Eclypsis, Boca Raton, FL). Cost accounting uses allocation statistics or relative value units to assign direct and indirect departmental costs to each supply or service item. The sum of the supply or service items utilized by a patient determines postplacement cost for the patient. Device-specific postplacement cost did not include the expense of preoperative evaluation and endograft placement. These data therefore represent the actual costs to the institution and are neither the charges to the patient or payor nor the reimbursement data.

Additional included costs were outpatient visits, institutional overhead costs, and professional fees. Outpatient visit expenses were calculated using a time-based formula assigned through the use of evaluation and management codes. The institutional overhead costs were added to the direct patient care by a factor of 30%. This conversion factor is consistently applied by Hospital Decision Support with minimal variability per month. The institutional overhead cost accounts for expenses from departments not directly involved in patient care (e.g., housekeeping, finance, maintenance), facility costs, and interest expense on borrowings. Professional fees were calculated using a department-specific cost-to-charge ratio. Mean January to June 2006 costs were applied to earlier years' costs to ensure data consistency.

Our follow-up protocol for both device types was the same. Patients underwent an initial outpatient visit at 2 weeks after surgery. This was followed by outpatient visits at 1, 6, and 12 months and yearly thereafter. At the time of these visits, abdominal X-rays (AXRs; anteroposterior, lateral, and two obliques) and computed tomographic (CT) scan of the abdomen and pelvis (2.5-3 mm axial images, with and without intravenous contrast) were performed. In those patients with renal insufficiency, abdominal ultrasound was used for surveillance. If a patient underwent a secondary procedure, follow-up visits and the protocol were restarted. All devices were placed by two attendings (W. C. S. and S. R. M.), who closely followed this surveillance regimen. Patients participating in endograft Food and Drug Administration trials followed the same postplacement protocols after the initial hospitalization.

The number and types of secondary procedures and endoleaks were determined for each device. Secondary procedure was defined as any procedure related to the aneurysm or endograft following discharge from the hospital for the initial placement. The number and type of endoleaks for each device were also determined. Only endoleaks seen on imaging at 1 month or afterward were included. The indications for secondary procedures for endoleak were the presence of a type I or type III endoleak or a type II endoleak with significant sac expansion (>5 mm). In recent years, translumbar glue embolization for treatment of type II endoleaks has been favored, although coil microembolization was used previously.

Statistical Analysis 

Data are expressed as mean ± standard error (SE). Patient demographics, outpatient visits, and imaging were compared using the χ² test. Cost data were analyzed and the follow-up time comparison made using the Wilcoxon two-sample test. Kaplan-Meier life-table analysis was utilized in device comparisons of secondary procedures and endoleaks to negate any bias created by different follow-up times. p < 0.05 was considered statistically significant. Statistical analysis was performed using Statistical Analysis System (SAS) software, version 8.2 (SAS Institute, Cary, NC).

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Results 

Of the completed EVARs during the study period, 131 were included in the final cost analysis. Reasons for exclusion were death (n = 35), <1 year since EVAR (n = 32), lost to follow-up (n = 25), follow-up at another institution (n = 15), and refusal of further treatment (n = 12). This resulted in a final cost analysis with 55 AneuRx and 76 Zenith patients.

Patient characteristics were compared for each device. Patient age, abdominal aortic aneurysm size, male-to-female ratio, coronary artery disease, chronic obstructive pulmonary disease, diabetes mellitus, and hypertension did not differ significantly between AneuRx and Zenith (Table I). Only the rate of preoperative chronic renal insufficiency, defined as a baseline creatinine ≥1.5 (AneuRx 5.5%, Zenith 17.1%; p < 0.05), and tobacco use (AneuRx 83.6%, Zenith 64.5%; p < 0.05) differed between the device groups. Mean follow-up times for the two groups were 38.5 ± 5.2 months (AneuRx) and 32.8 ± 3.8 months (Zenith, p = 0.12). There were no aneurysm-related deaths in the final cohorts.

Table I. Patient characteristics

NS, not significant; AAA, abdominal aortic aneurysm; COPD, chronic obstructive pulmonary disease.

There were 51 secondary procedures overall for the two devices (27 AneuRx in 17 patients, 24 Zenith in 10 patients) (Table II). The greater number of mean secondary procedures per patient in the Zenith (2.4) compared to the AneuRx (1.6, p = 0.39) group is a result of two of the Zenith patients requiring six secondary procedures each. The highest number of secondary procedures in the AneuRx group was four in one patient. The most common adverse event for both devices during follow-up was a type II endoleak (AneuRx n = 9, Zenith n = 8) (Table III). All of the adverse events led to a secondary procedure with the exception of eight type II endoleaks, which were monitored without the need for intervention.

Table II. Secondary procedures

IMA, inferior mesenteric artery; PTA, percutaneous transluminal angioplasty.

Table III. Adverse secondary events for each device

Kaplan-Meier analysis demonstrated a significantly higher incidence of secondary procedures over time with AneuRx compared to Zenith (p < 0.05.) (Fig. 1). Freedom from secondary procedures for the AneuRx endograft was 87.3%, 85.0%, 69.8%, 61.6%, and 51.3% at 1, 2, 3, 4, and 5 years, respectively. For the Zenith endograft, freedom from secondary procedures was 94.7%, 89.1%, and remained at 80.4% for years 3, 4, and 5 (p < 0.05) , respectively. The most common secondary procedure for both groups was diagnostic angiograms (n = 11 AneuRx, n = 9 Zenith). In the AneuRx group, nine patients went on to have additional secondary procedures; and in the Zenith group, all of the patients with diagnostic angiograms later had additional interventions. The most costly secondary procedure for the AneuRx device group was delayed open conversion (n = 4) for a mean cost of $21,382 ± $3,130. Two conversions were due to endoleaks alone (type I, type III), one for migration and endoleak (type I), and one due to aneurysm expansion (endotension). The most costly procedure for the Zenith group was endograft explantation with extra-anatomic bypass (n = 2) for endograft infection, with a mean cost of $57,681 ± $6,464. These infrequent but costly secondary procedures accounted for 26.2% of the cumulative cost for the AneuRx and 36.2% for the Zenith.

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• Fig. 1 

  Freedom from secondary procedures by Kaplan-Meier analysis.

A higher rate of endoleaks with the AneuRx endograft compared to the Zenith was demonstrated over time using Kaplan-Meier analysis (Fig. 2). Freedom from endoleaks for the AneuRx endograft was 80.0%, 80.0%, 74.1%, 70.0%, and 58.3% at 1, 2, 3, 4, and 5 years postplacement, respectively. For the Zenith endograft, freedom from endoleaks was 89.5%, 89.5%, and remained at 83.7% for years 3, 4, and 5 (p = 0.05), respectively. A total of 16 patients with AneuRx endografts had 17 endoleaks (five type I, nine type II, three type III), while 11 of the Zenith patients had 12 endoleaks (zero type I, eight type II, four type III).

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• Fig. 2 

  Freedom from endoleaks by Kaplan-Meier analysis.

Postplacement costs 

For the patients with the AneuRx device, the mean cost for the first year was $2,784 ± $632. For years 2-5, the cost was $2,056 ± $910, $2,961 ± $1,179, $2,794 ± $1,225, and $1,871 ± $848, respectively. For patients with the Zenith device, the mean cost was $2,854 ± $887 for the first year. For years 2-5, the mean device cost was $966 ± $284, $1,516 ± $815, $755 ± $323, and $4,515 ± $3,200, respectively. The 5-year cumulative postplacement costs were $12,465 (AneuRx) and $10,606 (Zenith) (p = 0.22) (Fig. 3).

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• Fig. 3 

  Cumulative 5-year postplacement costs.

During the first postplacement year, the AneuRx cohort averaged 3.5 ± 0.1 outpatient visits and 2.7 ± 0.1 CT scans, while the Zenith means were 3.9 ± 0.1 outpatient visits (p = 0.08) and 2.7 ± 0.1 CT scans (p = 0.08). There was a significant difference only in AXRs during this year (AneuRx 2.3 ± 0.1, Zenith 2.7 ± 0.1; p < 0.05). For the subsequent years 2, 3, and 5 of follow-up, the number of outpatient visits (AneuRx 1.2 to 1.3 ± 0.02, Zenith 0.9 to 1.0 ± 0.02), CT scans (AneuRx 1 to 1.3 ± 0.1, Zenith 0.8 to 1.0 ± 0.1), and AXRs (AneuRx 1.0 to 1.3 ± 0.2, Zenith 0.9 ± 0.1) were similar. Only in year 4 were additional significant differences in outpatient visits (AneuRx 1.8 ± 0.2, Zenith 1.0 ± 0.1; p < 0.05), CT scans (AneuRx 1.5 ± 0.2, Zenith 0.9 ± 0.1; p < 0.05), and AXRs (AneuRx 1.5 ± 0.2, Zenith 1.0 ± 0.1; p < 0.05) seen.

The cumulative cost components for AneuRx were secondary procedures (59.4%), radiologic studies (29.2%), outpatient visits (6.7%), laboratory costs (0.2%), and hospital readmissions (4.2%). Radiologic studies comprised the largest cost component for the first postplacement year, while secondary procedures comprised the largest cost component for the remaining years. For the Zenith device, the cost components were secondary procedures (56.4%), radiologic studies (35.0%), outpatient visits (8.0%), and laboratory costs (0.7%). Radiologic studies comprised the largest cost components in years 1 and 4, while secondary procedures comprised the largest cost component for all other years.

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Discussion 

It has been shown that long-term postplacement costs after EVAR contribute a significant cost to the overall EVAR expense.¹, ², ³, ⁴, ⁵ The presence of endoleaks and the need for secondary procedures have a significant impact on the cumulative postplacement costs.⁶ A number of previous studies have demonstrated device-specific outcomes and results.⁷, ⁸, ⁹, ¹⁰ However, there have been no previous device-specific postplacement comparisons. In this study, the postplacement costs of the AneuRx and Zenith devices are characterized.

The 5-year cumulative mean postplacement cost for the AneuRx device was $12,465, while the postplacement cost for the Zenith was $10,606 (p = 0.22). This 15% cost reduction in the Zenith device, however, was not statistically significant. Because of the relatively small number, a type II statistical error is possible. Secondary procedures and radiologic studies accounted for the largest cost components for both devices. There were fewer secondary procedures and endoleaks in the Zenith cohort.

While there have been no prior direct comparisons of device-specific postplacement costs, there have been studies evaluating follow-up costs with predominantly one device. Prinnsen et al.¹¹ reported postplacement costs for 77 patients with a mean follow-up of 19.9 months using the Ancure endovascular system (Guidant, Menlo Park, CA) in all but two patients. Five-year follow-up cost was $9,729. In an Australian series of 54 patients with a median follow-up of 12 months using primarily the Zenith endograft, mean yearly postplacement costs were $999.¹² Our postplacement costs were somewhat higher but also reflect a longer follow-up and capture of late secondary procedures.

The largest cost component for both the AneuRx and Zenith devices was secondary procedures. At 5 years, there was a significant difference in freedom from secondary procedures using Kaplan-Meier life-table analysis (AneuRx 51%, Zenith 80%; p < 0.05). As secondary procedures have the greatest impact on long-term postplacement costs, this difference may have influenced the trend toward increased cost with the AneuRx device. Late secondary procedures also had a dramatic effect on the 5-year cumulative costs. Through postplacement year 4, the cost in the AneuRx cohort was 43% greater than that in the Zenith cohort. However, with inclusion of two costly late secondary procedures (endograft explantation, iliac endocuff placement for a type III endoleak) in the fifth year, this difference was reduced to 15%. At 5 years by Kaplan-Meier life-table analysis, there was also a reduction in freedom from endoleaks using the Zenith device (AneuRx 58%, Zenith 83%; p = 0.05). In our experience, the presence of endoleaks increased the intensity of surveillance imaging to every 3-6 months.

Other cost components contributed to postplacement expenses as well. Radiologic studies comprised 29.2% and 34.9% of the total cost for the AneuRx and Zenith devices, respectively. While there were only a few differences in mean number of imaging studies between devices, these imaging studies represent a potential source of further cost reduction. In selected patients, alternate surveillance imaging protocols with different modalities or frequency may be appropriate.¹³, ¹⁴ The remaining cost is primarily from outpatient visits (AneuRx 6.9%, Zenith 8.0%). Reduction in frequency of these outpatient visits may provide a lesser source of further cost reduction as their frequency often parallels the surveillance imaging. Appropriate patients for reduced surveillance regimens still need to be defined and will require further study.

There are a few study limitations. First, many of the AneuRx patients had their endografts placed earlier in our experience, while the Zenith endograft was used primarily in later years. To minimize the learning curve effect, however, the initial 50 patients were excluded. Furthermore, changes that have occurred in practice patterns over time, such as less frequent use of diagnostic angiograms, less aggressive treatment of type II endoleaks, and more aggressive approach to iliac coverage at the initial procedure may potentially result in lower device-specific postplacement costs for currently placed endografts. Also, device and technical modifications for the AneuRx and Zenith, as well as alterations in surveillance imaging, make it possible that devices currently being placed will have lower postplacement costs. Second, there are limitations to the cost data. As a single-institution analysis, there may be regional and hospital-specific variations to overhead and other labor-related cost components when applied to other regions and institutions. Also, a number of patients were lost to follow-up. However, our data represent a “real-world” postplacement cost as opposed to an ideal postplacement cost. In an ideal practice setting with higher patient compliance, postplacement costs would be potentially greater.

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Conclusions 

There was a reduction in secondary procedures and endoleaks seen with the Zenith compared to the AneuRx device. However, the corresponding 15% reduction in long-term postplacement costs was not statistically significant. Secondary procedures and surveillance imaging account for >88% of the follow-up expenses for both devices. Improvements in device design and technique to minimize secondary procedures, endoleaks, and need for surveillance imaging may reduce a specific device's postplacement costs.

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