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Wilt TJ, Lederle FA, MacDonald R, et al. Comparison of Endovascular and Open Surgical Repairs for Abdominal Aortic Aneurysm. Rockville (MD): Agency for Healthcare Research and Quality (US); 2006 Aug. (Evidence Reports/Technology Assessments, No. 144.)

  • This publication is provided for historical reference only and the information may be out of date.

This publication is provided for historical reference only and the information may be out of date.

Cover of Comparison of Endovascular and Open Surgical Repairs for Abdominal Aortic Aneurysm

Comparison of Endovascular and Open Surgical Repairs for Abdominal Aortic Aneurysm.

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4Discussion

AAA are associated with considerable morbidity, mortality and health-care costs. Elective OSR has traditionally been considered the intervention of choice to reduce the risk of AAA rupture and improve survival in individuals at high risk of rupture. However, EVAR has become widely used based on belief that it may provide long-term prevention of ruptures with low intervention morbidity and mortality and improved length and quality of life. Approximately one-half of large AAA might be anatomically suitable for EVAR. Results from this systematic review provide the most up-to-date evidence related to the natural history, treatment, and costs associated with asymptomatic nonruptured infrarenal AAA. This report also evaluates evidence related to the relationship of surgical and hospital volume on outcomes for both OSR and EVAR.

AAA is predominantly a condition of older men with a much lower prevalence in younger persons and women. The strongest known predictor of AAA rupture is initial or attained size. Patients with AAA <5.5 cm have an annual risk of rupture of approximately 1 percent. For AAA <5.5 cm in diameter, high-quality RCT results demonstrate that active surveillance with ultrasound and delayed OSR (if AAA attains a diameter of ≥5.5 cm or the patient develops aneurysm related symptoms) results in equivalent mortality but lesser morbidity and operative costs due to fewer interventions compared to immediate OSR. Therefore, for AAA <5.5 cm, active surveillance and delayed OSR if AAA diameter exceed 5.5 cm (or in those that develop symptoms consistent with impending rupture) results in comparable long-term survival and quality of life, fewer OSR, and lower costs than immediate OSR regardless of age or gender. There are no RCT evaluating EVAR in these patients.

Among individuals with large AAA and refusing or medically unfit for OSR, the 1 year rupture risk may exceed 10 percent in AAA >6 cm and for AAA of >8 cm, the risk may exceed 25 percent at 6 months. For AAA ≥5.5 cm and suitable for EVAR, high-quality RCTs have been conducted outside the U.S. and may have used some EVAR devices that are not approved for use in the U.S. Their results demonstrate that compared to OSR for medically fit patients, EVAR is associated with lower perioperative morbidity and mortality and persistent reduction in AAA-defined mortality to 4 years, though the latter may be due, at least in part, to ascertainment bias for later term cause of death. EVAR did not improve longer term overall survival or health status and was associated with greater complications, need for reintervention, long-term monitoring, and costs. Because decisions regarding the risks and benefits of AAA treatments should incorporate a long-term time frame, additional followup information beyond 4 years is needed. There are insufficient data to determine whether outcomes varied according to device type.

For the minority of patients with AAA ≥5.5 cm judged medically unfit for OSR, one high-quality RCT conducted in the U.K. with EVAR devices that may not be approved for U.S. use demonstrated that EVAR did not improve survival at 3 years or health status and costs more than no intervention. More than 60 percent of the no intervention group died indicating that longer followup was unlikely to alter results. Refinements in EVAR devices or provider experience may result in different outcomes. Therefore a RCT conducted in the U.S. with currently approved EVAR devices in these patients is indicated. However, unless results from such a RCT refute findings from EVAR-2, the RCT data provide the highest quality evidence available for treatment decision making and do not support the widespread practice of using EVAR to treat AAA in patients judged to be too sick for OSR. Patient treatment preference is difficult to ascertain. How the results of RCT influence patient and provider treatment preference in the U.S. is not known.

Data from nonRCT are limited by lack of randomization as well as incomplete followup reporting of entered patients. They cannot be used as substitutes for RCT to evaluate the comparative effectiveness and adverse effects of AAA treatment options. Few studies provided an evaluation according to device or patient characteristics. None represent head to head comparisons from RCT. Furthermore, patient or aneurysm factors could influence outcomes. Therefore, it is hazardous to make definitive statements regarding relative safety or effectiveness. While it is not possible to make direct comparisons with RCT, most reports explicitly stated patients were candidates for OSR. Baseline patient characteristics, AAA diameter, 30 day and 2 year overall, and AAA mortality as well as EVAR conversion rates and secondary interventions for included patients were similar to those from EVAR-1 and DREAM. None of these reports assessed EVAR in patients with AAA ≥5.5 cm and considered “medically unfit for OSR.” One report evaluated outcomes of EVAR and OSR in a retrospectively defined “high surgical risk” subgroup of patients entered into any of five nonrandomized multicenter IDE studies leading to FDA approval of EVAR devices. Inclusion criteria for the IDE studies required that patients were candidates for OSR, though in one study patients were prospectively defined as being at high risk for OSR due to age >80 years or other pathophysiologic conditions. It is not known whether any were judged medically unfit for OSR. After 4 years, deaths categorized as due to AAA were similar between EVAR and OSR patients. Overall-survival in EVAR treated patients was 10 percent lower compared to OSR, though this difference was not statistically significant.

Because of the relatively low 30-day procedure related morbidity and mortality, treatment with EVAR of patients with smaller AAA has occurred. Therefore, while the total number of interventions for AAA has remained relatively constant over time, the proportion of patients treated with EVAR has increased. There are no published investigations of relationships between hospital or physician volume and any outcome of EVAR of AAA. Published and ongoing EVAR RCT have required that investigators and their facilities have experience in use of this procedure. The threshold for permitting participation varies from 5 to 20 and were not based on evidence.

The volume of OSR procedures done by hospitals and physicians to repair unruptured AAA was inversely associated with short-term mortality in the 1990s when EVAR procedures were being investigated. Surgeon volume may explain a large portion of the effect of hospital volume, although hospital volume appears to have an effect that is not related to surgeon volume or surgeon specialty. Uncontrolled risk factors might account for some of the volume effects. The one study that was able to control for preoperative clinical measures did not find a significant association between hospital volume and mortality.139 Otherwise, the reasons for the observed relationships between the volume of procedures done by hospitals or surgeons over a period of time and short-term mortality have not been clearly established. The imprecision inherent in measuring outcomes of very low-volume providers isn't always taken into account and may unduly influence estimates in some studies. Even though policymakers such as the Leapfrog group have somewhat arbitrarily selected cutoffs to define preferred ‘high’ volume hospitals for OSR of AAA, investigators have not identified optimal thresholds for grouping providers by volume in an effort to improve outcomes. Furthermore, this question needs to be revisited since EVAR has replaced OSR in a substantial percentage of AAA.

The cost effectiveness of EVAR relative to OSR is difficult to determine for several reasons: there are no long term (>4 year) outcome data from RCT of EVAR versus OSR; evolving EVAR technological refinements and provider experience may push EVAR towards being an effective and cost-effective alternative to OSR; it is difficult to extrapolate the cost experience in one country to that in another with a different health care and payment system; the perspective of the concerned party is critical in such analyses.

Case series focusing on hospital costs generally found that EVAR costs more to perform than OSR, primarily due to the cost of the prosthesis. The high cost of the EVAR prosthesis is partially offset by reduced hospital and intensive care unit length of stay, operating time, and necessity for blood transfusion relative to OSR. More comprehensive cost analyses noted the higher followup costs for EVAR.

None of the Markov cost effectiveness models had accurate data on the complication and reintervention rates associated with EVAR. Although the Michaels et al. study is based on the literature published through September 2004, several case series have come out since then, and data from midterm results of RCTs were not included.17

Results from additional RCTs, comparing EVAR and OSR for large AAA and EVAR versus surveillance for small AAA conducted in the U.S. have not yet been published. It is not clear how these costs would directly relate to U.S. settings. Trials conducted outside the U.S. do not reflect U.S. norms associated with resource valuation, utilization of health care resources, practice variation, and U.S. health care expertise. Decisions based on costs may differ with the locus. For example, hospitals may be willing to consider trading higher procedural costs for shorter lengths of stay.

Data from RCTs demonstrate that for small AAA (<5.5 cm) immediate OSR costs more and does not improve survival compared to active surveillance and delayed elective intervention. For large AAA (≥5.5 cm) among patients fit for OSR, EVAR has greater short- and long-term costs, does not improve overall survival or quality of life beyond 1 year, and is associated with greater long-term complications, need for reintervention, and long-term monitoring compared to OSR. EVAR is associated with shorter hospital and intensive care unit length of stay, reduced AAA mortality, and lower 30-day morbidity and mortality, compared with OSR. In patients with AAA ≥5.5 cm and judged medically unfit for OSR, EVAR did not improve survival or quality of life among those who were alive and was associated with higher costs compared to no intervention.

The analyses conducted in the UK reflect concerns relevant to the NHS that may not be as important in a U.S. context. For example, whereas EVAR's potential to free up hospital beds may be important to NHS hospitals pressed for space, in the American context this aspect of EVAR has more salience for hospitals trading off LOS for a more expensive EVAR prosthesis under a fixed payment DRG reimbursement approach.

Other issues regarding the published data used in the Markov models include the transferability of results found in case series studies to different patient populations, e.g., of different aneurysm size. As new clinical devices are continually being introduced in the market, technological improvements may change the mortality and morbidity rates associated with EVAR in particular. The evidence of a learning curve or improvements in device manufacturing associated with EVAR may be associated with a lower long-term mortality, morbidity, and need for monitoring and reintervention that might someday demonstrate that EVAR is a cost effective alternative to OSR. Finally, because the 30-day mortality rates associated with OSR are variable, the significance of the differences in mortality rates between EVAR and OSR is obscured. The variability associated with operative mortality translates to greater uncertainty and higher risk to patients considering OSR. If improvements in long-term morbidity and mortality with EVAR are demonstrated in the future, this may make EVAR a favorable alternative to OSR from the patient's perspective.

When conducting CEA, a common concern among researchers is that one needs to account for the fact that patients who die cost less in terms of health care expenditures than patients who live longer. The treatment arm that results in higher mortality rates would thus have lower costs reflected in the numerator of the cost effectiveness ratio. The standard approach to adjusting the cost effectiveness ratio for deaths is to assume that the QOL associated with death is zero in the denominator.160 The assumption is that QOL takes into account the disutility associated with morbidity/mortality. As long as the QOL scale also reflects the disutility of lost earnings, solely relying on the QOL to account for deaths in the denominator is permissible. If the QOL scale does not reflect lost earnings, then the numerator must reflect the patients' lost earnings as part of the cost associated with each treatment. Although some might attribute the QOL associated with death as zero, others may think of death as having a higher QOL than other outcomes, such as living with pain.

Different components of cost may have different salience in different national health contexts. When comparing results of economic analyses across countries, there is currently no consensus or standard on how to do this. Simply factoring in the foreign exchange rate, for example, overlooks the variance in utilization and cost estimates across countries due to differences in physician practice patterns, resource valuation, and resource use. Reed et al. discuss the strengths and weaknesses of various methods used to pool cost estimates across countries.164 Methods are differentiated according to whether measures of effectiveness, resource utilization, and cost are derived from one or multiple countries. Strengths and weaknesses are based on balancing concerns about generalizability, transparency, and statistical power. Tradeoffs exist between trying to keep things simple enough for other researchers to implement (e.g., a one-country costing approach) and losing internal validity associated with a multinational costing approach. One-country costing disrupts the theoretical relationship between relative costs and resource use. Reed et al. note that using relatively high U.S. unit costs overestimates total costs as well as the absolute difference in costs between treatment groups, inflating the numerator of an ICER.164

Recommendations for Future Research

  • Results from nonrandomized trials, case-series, or FDA reports are inadequate to accurately assess the relative effectiveness and safety of treatments for AAA. The highest priority for future research to guide clinical care is to conduct long-term RCTs in the U.S. to assess whether RCT results of EVAR conducted in Europe apply to U.S. settings. These include EVAR vs. OSR for AAA ≥5.5 cm in patients judged medically fit for OSR (analysis of results according preplanned categories of AAA, operative risk, gender, and device characteristics appears warranted), EVAR versus active surveillance for AAA <5.5 cm, and EVAR versus no intervention for AAA ≥5.5 cm in patients medically unfit for OSR.
  • Effective strategies are required to disseminate and implement the findings from published high-quality RCTs to patients, providers, health-care organizations, and payers.
  • Additional information on the benefits and risks of treatments in women are needed.
  • Refinements in EVAR devices, technique, and interventionist team are required to reduce complications and need for long-term followup.
  • Although studies cannot avoid measurement error associated with outcomes resulting from incorporating new devices into them, more research is needed to identify whether outcomes for EVAR vary according to device manufacturer or type and patient or aneurysm characteristics. Ideally, these would be obtained by conducting direct comparison RCTs.
  • Consistent/validated definitions of outcomes including AAA mortality; complications, and need for reintervention are required to assist clinicians, investigators, policy makers, and patients to evaluate relative safety and effectiveness of treatment options. In particular, cause of death ascertainment beyond 30 days or the initial hospitalization is problematic. Reducing ascertainment bias likely requires rigorous adjudication of all deaths including use of autopsy and/or post-mortem imaging.
  • Conduct RCTs to determine whether medical therapy slows AAA enlargement or rupture. Previous trials were inadequately powered to provide clinically meaningful results.
  • Improve data submission, followup, and cause of death ascertainment in registries.
  • Improvement in medical management of patients with large AAA considered unacceptable for OSR is needed.
  • Specific studies of EVAR are needed to characterize the hospital and physician volume-outcome relationship, if any. The validity of methods used to identify and count EVAR procedures should be examined and reported. Studies should measure volume in a consistent manner and focus on outcomes defined in reporting standards including clinical success, continuing success, complications, and return to preprocedure activity levels. Risk adjustment should include patient demographics, comorbidity, morphology of the aneurysm and access vessels, device characteristics, and any other variables that could have a substantial influence on the outcomes under investigation. Rigorously developed and tested regression models and examination of the sensitivity of results to the method of analysis would be useful. Most likely, representative prospective registries will be needed to perform a proper indepth analysis to determine whether and how the volume of endovascular procedures done by hospitals or physicians to repair AAA relate to beneficial or adverse outcomes. Ideally, future studies would strive to characterize the functional form of volume-outcome relationships and explain why they exist. The volume-mortality relationship for OSR of AAA needs to be reexamined in the EVAR era.
  • Future cost analyses studies should include short- and long-term followup data, either collected prospectively on all patients or incorporated from RCTs into Markov models.
  • Studies should follow a standardized approach to analyzing costs and effectiveness associated with the two procedures. Studies should explicitly describe the methods used to calculate costs and should include the following categories: direct medical care costs, institutional overhead costs, patient travel costs, and patients' time and/or lost earnings. The collection of these costs should be carefully itemized and described.
  • Studies conducting prospective data collection in the United States taking a societal perspective are needed. Where appropriate, data should be collected on the patient's time taken off work or other activities to travel and attend medical appointments, whether on an inpatient or outpatient basis, and to obtain prescriptions.
  • Data on United States patient's QOL, where the treatment of the QOL associated with lost earnings and death is explicitly stated, should also be collected.

Conclusions

AAA are associated with considerable morbidity, mortality and health-care costs. Patients with AAA <5.5 cm have an annual risk of rupture of approximately 1 percent. For AAA <5.5 cm in diameter high-quality RCT results demonstrate that active surveillance with ultrasound and delayed OSR (if AAA attains a diameter of ≥5.5 cm or the patient develops aneurysm related symptoms) results in comparable long-term survival and quality of life, fewer OSR, and lower costs than immediate OSR regardless of age or gender. There are no RCTs evaluating EVAR in these patients.

Among individuals refusing or medically unfit for OSR the 1-year rupture risk may exceed 10 percent in AAA >6 cm and for AAA of >8 cm, the risk may exceed 25 percent at 6 months. For AAA ≥5.5 cm and suitable for EVAR, high-quality RCTs have been conducted outside the U.S. and may have used some EVAR devices that are not approved for use in the U.S. Their results demonstrate that, compared to OSR, EVAR is associated with lower perioperative morbidity and mortality and persistent reduction in AAA-defined mortality to 4 years, though the latter may be due, at least in part, to ascertainment bias for later term cause of death. EVAR did not improve longer term overall survival or health status and was associated with greater complications, need for reintervention, long-term monitoring, and costs.

For the minority of patients with AAA ≥5.5 cm and judged medically unfit for OSR, one high-quality RCT conducted in the U.K. and with EVAR devices that may not be approved for use in the U.S. demonstrated that EVAR did not improve survival or health status and costs more than no intervention.

There are no data adequate to estimate the effect of hospital or physician volume on EVAR outcomes and identify a volume threshold for policymakers. A volume outcome relationship for OSR has been shown for surgery prior to the introduction of EVAR, but none since.

The cost effectiveness of EVAR relative to OSR is difficult to determine for several reasons: there are no long term (>4 year) outcome data from RCT of EVAR versus OSR; evolving EVAR technological refinements and provider experience may push EVAR towards being an effective and cost-effective alternative to OSR; it is difficult to extrapolate the cost experience in one country to that in another with a different health care and payment system; and the perspective of the concerned party is critical in such analyses.

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