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1
Decision Analysis and Technology Assessment Group, Department of Radiology,
Massachusetts General Hospital and Harvard Medical School, Zero Emerson PI.,
Ste. 2H, Boston, MA 02114.
2
Department of Radiology, University Medical Center Utrecht, Heidelberglaan
100, 3584 CX Utrecht, the Netherlands.
3
Department of Radiology, Brigham and Women's Hospital, 75 Francis St., Boston,
MA 02115.
4
Information Systems, Brigham and Women's Hospital, 1249 Boylston St., Boston,
MA 02215.
5
Program for the Assessment of Radiological Technology, Department of
Epidemiology and Biostatistics, Rm. EE21-40a, Erasmus Medical Center,
Rotterdam, P. O. Box 1738, 3000 DR Rotterdam, the Netherlands.
Received May 21, 1999;
accepted after revision January 26, 2000.
Supported by a PIONIER award from the Netherlands Organization for
Scientific Research and by a Van Walree award from the Dutch Royal Academy of
Sciences.
Abstract
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MATERIALS AND METHODS. Lifetime costs and quality-adjusted life expectancy were estimated using a Markov decision model for a hypothetic cohort of patients with life-style-limiting claudication caused by an iliac artery stenosis for whom a percutaneous intervention was indicated. Various percutaneous treatment strategies were evaluated, each consisting of an initial intervention followed by a secondary intervention. Procedures considered were angioplasty alone and angioplasty with selective stent placement.
RESULTS. From the perspective of the interventional radiology department, angioplasty with selective stent placement costs more than angioplasty alone ($2926 versus $2106). Taking into account follow-up costs and procedures for long-term failures, the cost differential was reduced because of a lower failure rate of selective stent placement ($13,158 versus $12,458, respectively). Treatment strategies using angioplasty with selective stent placement (as an initial procedure or including reintervention) dominated treatment strategies using angioplasty alone (incremental cost-effectiveness ratio was $7,624-8,519 per quality-adjusted life-year gained).
CONCLUSION. Angioplasty with selective stent placement is a cost-effective treatment strategy compared with angioplasty alone in the treatment of intermittent claudication in the United States.
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In the treatment of iliac artery occlusive disease, multiple reports have been published suggesting that stent placement increases patency compared with angioplasty, and a meta-analysis of these cohort studies showed that stent placement reduced the risk of failure by 39% compared with angioplasty alone [1]. Although the reported benefits in clinical outcomes of stent placement are of interest to the physician and the patient, policy makers are also concerned with the extra costs this procedure may have and if this treatment strategy is going to be used more frequently, the deleterious impact that it may have on health care budgets.
A randomized clinical trial and cost-effectiveness analysis performed in the Netherlands showed that angioplasty with selective stent placement was equally effective and less costly than direct stent placement and that it was a cost-effective treatment strategy compared with angioplasty alone [2, 3]. Whether the result of the reported analysis is generalizable to policy making in other countries remains unclear. That analysis included Dutch cost estimates and because of existing differences in finance systems across countries and regulations within a hospital, it is unlikely that these data will be similar in, for example, the United States. The purpose of this study was to assess the direct costs of angioplasty and stent placement in the United States and to evaluate the cost-effectiveness of the treatment strategies (angioplasty alone and angioplasty with selective stent placement) in patients with intermittent claudication caused by an iliac artery stenosis.
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In the cost-effectiveness analysis, we calculated the incremental cost-effectiveness ratios when a more effective strategy was also more expensive [5]. That is, additional costs were divided by the effectiveness gained (i.e., quality-adjusted life expectancy) in comparison with the next best strategy after dominated strategies were eliminated. A strategy was considered dominated if the costs were higher and the quality-adjusted life expectancy lower than another strategy, or a strategy was considered "inferior by extended dominance" if another strategy yielded greater effectiveness and had a lower incremental cost-effectiveness ratio [5]. In both situations, the treatment strategies are unrealistic alternatives and are therefore eliminated before calculating the incremental cost-effectiveness ratios [5].
To convert future dollars and future health outcomes to their present value, both future costs and benefits were discounted at 3% per year, as is recommended by the U. S. Public Health Service Panel on Cost-Effectiveness in Health and Medicine [5]. In a sensitivity analysis, we varied the discount rate (i.e., 0.0-0.10).
Effectiveness
The decision model was used to estimate quality-adjusted life expectancy
for each treatment strategy on the basis of morbidity and mortality data,
patency results, and quality-of-life data.
Table 1 shows the baseline
values included in the model. The values were retrieved from a published
meta-analysis and a randomized controlled trial
[1,
2]. The same effectiveness data
were included in a previously published cost-effectiveness analysis
[2]. In a sensitivity analysis,
we varied the discount rate (i.e., 0.0-0.10), the age of the patient (i.e.,
40-85 years), and the quality-of-life score (i.e., 0.70-0.90) before and after
treatment to test if these variables influenced the cost-effectiveness ratio
[5]. Furthermore, to give an
estimate of the cost-effectiveness of the treatments in patients with critical
ischemia or occlusion in the arteries, we used a relative risk for long-term
failure of patency for critical ischemia versus claudication (i.e., 1.54) and
a different initial technical success rate for occlusions (i.e., 0.80 for
angioplasty and angioplasty with selective stent placement)
[1].
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Costs
To perform the economic analysis from a societal perspective, the direct
health care and non-health care costs incurred with the treatment were
included. Hence, we assessed the costs of the interventional radiology
department, additional hospital costs, patient costs, and additional societal
costs. The costs were estimated from patients with iliac artery occlusive
disease admitted to the Brigham and Women's Hospital in Boston. We used
published guidelines for cost assessment from the Dutch Guidance Group for
Future Scenarios in Health Care
[7] and from the United States
Panel on Cost-Effectiveness in Health and Medicine
[5]. All costs were converted
to 1998 United States dollars using the consumer price index
[8]. The total procedure costs
(Table 2) were included in the
baseline analysis.
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The interventional radiology department.To estimate the actual costs, we performed microcosting of 12 procedures. The nursing sheet was reviewed for details regarding time and motion, and the treatment report and inventory database were reviewed for details regarding all materials used and their associated costs. To calculate the personnel costs, the mean time spent performing the procedure by various disciplines was multiplied by the total compensation of that discipline and summed for the specific treatment strategy. We used the gross salary and included fringe benefits and social security taxes to the employer [7]. To calculate the mean procedure cost, the distribution of one-sided versus two-sided lesions was taken into account (72% and 28%, respectively). Detailed information of a two-sided angioplasty was unavailable; therefore, we assumed that the procedure time of a two-sided angioplasty was similar to that of a one-sided angioplasty with stent placement procedure, which was shown to be the case in the Dutch Iliac Stent Trial [2]. In addition, the material costs were assumed to be equivalent to the costs of a one-sided angioplasty with the additional costs of an extra balloon, a sheath, and extra contrast material (i.e., in total estimated at $250). Cost of the electric equipment in the angiography room was calculated per treatment strategy taking into account the initial investments, additional investments, expected lifetime, depreciation, number of hours used, number of procedures performed, and the duration of the procedure [9]. Costs were adjusted for the amortization of capital expenditures [9]. Maintenance of the equipment and the cost of housing were also calculated per strategy, taking into account the duration of the procedure.
Additional hospital costs.The costs for complications were estimated by multiplying the probability of a complication requiring treatment (4.8%) by the estimated cost for a bifurcation bypass, including additional hospital stay (i.e., assumed to be 6 days) [1, 10]. The other additional costs were estimated for 54 patients admitted to the Brigham and Women's Hospital undergoing diagnostic angiography followed by angioplasty alone (n = 38) or angioplasty plus stent placement for an inadequate angioplasty result (n = 16). These cost data were obtained from the hospital administrative and accounting system and are based on the charges for each admission multiplied by a department-specific, year-specific cost-to-charge ratio [11, 12]. The cost-to-charge ratios are determined each year per revenue center and are based on the annual costs and charges of each center. Annual costs per revenue center are computed on the basis of the center's operating expenses. In this calculation, costs incurred by non-revenue centers (such as housekeeping, information systems, and general hospital overhead) are distributed across revenue centers using some metric such as square footage.
Patient costs.Costs incurred by patients included time costs. Time costs were estimated by the monetary value of time expended for the intervention, which was estimated by multiplying the mean number of hospitalization days by the average gross earnings of a full-time 60-year-old male employee, including fringe benefits per day [5, 8, 13].
Additional societal costs.The additional societal costs were calculated with the Markov model and included costs of subsequent events, follow-up visits, and procedures performed for recurrent symptoms. Follow-up costs included the costs of two outpatient visits in the first year and one visit in the following years, and included the cost of the office visit, noninvasive diagnostic tests (treadmill testing, ankle pressure measurements, and duplex sonography of the treated segment), time costs, and medications. The costs of a follow-up visit ($407) were obtained from the American College of Radiology (Sunshine J, personal communication).
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All stents in the microcosting procedures were Palmaz stents (Cordis, Miami, FL), and the average number was 1.3 per procedure. Because the average price of a stent is $781, the difference in costs of materials between angioplasty and angioplasty with selective stent placement was mainly caused by the price of a stent. The mean length of stay was equal for both procedures (2 ± 2 days). Therefore, additional hospital costs and patient costs were equivalent for angioplasty and angioplasty with selective stent placement.
The costs of repeated procedures shown in Table 2 were based on the same procedure as the initial procedure. Whereas the procedure costs of angioplasty with selective stent placement are higher than the costs of angioplasty alone, during follow-up the costs of repeated procedures were lower because of a lower long-term failure rate of angioplasty with selective stent placement than of angioplasty alone (Table 2).
Table 3 shows the results of the cost-effectiveness analysis. Regardless of whether a secondary intervention for long-term failures was considered, angioplasty alone was dominated by the strategy angioplasty with selective stent placement in the treatment of a 60-year-old man with intermittent claudication and an iliac artery stenosis. The treatment strategy of angioplasty followed by selective stent placement was slightly more expensive but yielded higher patency rates and quality-adjusted life expectancy than the treatment strategy of angioplasty alone. The incremental cost-effectiveness ratio of angioplasty with selective stent placement was well below $10,000 per quality-adjusted life-year gained.
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Sensitivity analysis changing key assumptions such as duration of the procedure; distribution of one- versus two-sided lesions; price of a stent; discount rate; and patient characteristics such as age, quality of life, and disease severity showed that angioplasty with selective stent placement, followed by angioplasty with selective stent placement for long-term failures, was a cost-effective treatment strategy. Changing the patency data to those of procedures performed for critical ischemia, the cost-effectiveness ratio for initial and repeated angioplasty with selective stent placement was $15,558 per quality-adjusted life-year gained. For critical ischemia with occlusions, the incremental cost-effectiveness ratio was $23,034 per quality-adjusted life-year gained. However, more clinical and cost data of these subgroups are needed to substantiate these results. When the proportion of stent placement after angioplasty was changed to 90%, the treatment strategy initial and repeated angioplasty with selective stent placement was still preferred over strategies that included angioplasty alone (incremental cost-effectiveness ratio, $14,544 per quality-adjusted life-year gained).
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The cost-effectiveness analysis showed that treatment strategies starting with angioplasty followed by selective stent placement when the results were suboptimal were found to be more effective, with a lower cost-effectiveness ratio, than angioplasty alone. In a sensitivity analysis, we showed that, as expected, when the cost of the stent procedure decreased (e.g., because of placing fewer stents per procedure or decreasing the price of the stent itself), the treatment strategy angioplasty followed by selective stent placement would be favored even more. In addition, when the proportion of stent placements after angioplasty was increased to 90% (i.e., the angioplasty with selective stent procedure costs were $7,052), the outcome did not change substantially (i.e., the cost-effectiveness ratio remained below $25,000 per quality-adjusted life-year gained).
Furthermore, sensitivity analysis in which patient characteristics, including disease severity, were varied did not influence the outcome. However, more clinical data of patients with critical ischemia and occlusion in the iliac arteries are needed to give a policy recommendation with respect to these patient groups. Policy recommendations based on the baseline results suggest that when percutaneous treatment is considered for patients with iliac artery occlusive disease due to a stenosis, the preferred treatment strategy is to start with angioplasty followed by immediate stent placement if the results of angioplasty are unsatisfactory. In this patient group, direct stent placement would likely give an equal effect with higher costs, and angioplasty alone would reduce initial costs but because of lower effect would increase the costs during follow-up. We did not include the treatment strategy direct stent placement (i.e., all patients receive a stent) in our analysis. This strategy was previously compared with primary angioplasty followed by selective stent placement and showed equal effectiveness and higher costs [2, 3]. Because these results were based on a randomized clinical trial, we assumed this conclusion to be generalizable.
The finding of our study is in line with the results of a similar analysis performed previously including Dutch cost data [2]. To the best of our knowledge, other studies reporting costs or cost-effectiveness ratios of angioplasty with stent placement have not been published, and most studies reporting costs of iliac angioplasty were published before 1990 or were based on charges [14,15,16,17].
It is difficult to compare the costs of angioplasty and angioplasty with selective stent placement assessed in our study with those of the Dutch study [2] because hospitals and countries have their own administration and finance systems, making a complete standardized cost assessment and comparison impossible. Apart from the differences in the cost assessments, however, similarities exist between the two studies; for example, basically the same expenses were included, the patient populations were similar, the same discount rates were used, the costs were assessed in a teaching hospital, and the costs incurred by the interventional radiology department were retrieved by cost accounting [2, 3]. Therefore, we did compare the costs of angioplasty and angioplasty with selective stent placement incurred by the interventional radiology department between both studies and found that for both procedures costs were much higher in the present study. These higher costs were mainly caused by the cost of personnel and room and board. Because two authors were involved in both studies, the cost accounting data could be compared in more detail.
The difference in cost of personnel between the present study and the Dutch study is, to a large extent, explained by the difference in procedure time, which was longer in the present study. The most likely explanation for the longer procedure time is that consultation with the vascular surgeon regarding the decision to proceed with the tentatively planned percutaneous intervention took place while the patient lay on the angiography table immediately after diagnostic angiography. (Informed consent for a tentative interventional procedure was obtained before the diagnostic procedure.) In the Dutch study, the decision to proceed with the intervention could be expedited without obligatory consultation with the vascular surgeon because agreements were in place regarding the indications for percutaneous intervention. Another possible explanation for the longer procedure time may lie in the extent and technique of the diagnostic angiography performed. Whereas in the present study a full runoff study was always performed, in the Dutch study diagnostic angiography was limited to the aortoiliac region in 30% of cases because these patients had been fully examined with duplex sonography before intervention. Furthermore, differences in equipment and imaging technique may have led to differences in set-up and imaging time. Finally, in the United States, physicians are more vulnerable to medicolegal action than those in the Netherlands, which may incite them to take more time for the procedure.
A limitation of our study is that the cost accounting was based on a small sample size; the standard deviations, however, were small. Furthermore, several assumptions were made concerning the procedure time and material costs of a bilateral angioplasty procedure and the distribution of unilateral and bilateral lesions. If bias occurred, the costs might have been underestimated or overestimated. Cost of complications may have been overestimated because in the analysis we multiplied the proportion of complications requiring treatment, retrieved from the meta-analysis [1], by the costs of a bifurcation bypass, including additional hospital stay [10], which is likely the most expensive treatment that can be performed. Another limitation is that we did not perform cost accounting for the additional hospital costs. The additional hospital costs, however, showed face validity. Furthermore, costs were assessed in only one hospital in the United States. Because this hospital was a teaching hospital, the costs may have been over-estimated because of a possibly longer procedure time or more personnel involved. However, the resulting bias on the incremental costs used in the cost-effectiveness analysis can go either way but is unlikely to change the conclusion. Hence, the specific estimates should be interpreted with caution, and they may not be generalizable to other hospitals. Finally, in this paper we focused on the assessment of costs and the cost-effectiveness of angioplasty and angioplasty with selective stent placement for patients with iliac artery occlusive disease in the United States. The effectiveness data were used previously and were mainly retrieved from a published meta-analysis of cohort studies performed in several countries of Europe and the United States. We assumed generalizability of these data across countries.
In summary, we found differences in costs compared with previously reported costs, although the conclusions of the cost-effectiveness analysis were similar. Thus, in spite of differences in cost estimates, this did not influence the results of the cost-effectiveness analysis. Although encouraging, this generalizability across countries clearly does not necessarily apply to other clinical problems and other countries. In addition, by performing a cost accounting study and comparing the results with previously published costs, we were able to identify differences in various cost components. Such an approach may identify potential cost-saving strategies.
In conclusion, in the treatment of intermittent claudication due to an iliac artery stenosis, our results suggest that angioplasty followed by selective stent placement for unsatisfactory angioplasty results is a more cost-effective treatment strategy than angioplasty alone.
Acknowledgments
We thank Julie Lombara for her contribution in collecting patient data.
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