Volume-Outcome Relationships and Abdominal Aortic Aneurysm Repair

BACKGROUND: There is a well-established literature relating procedure volume to outcomes, but incorporating such information into clinical decision making is problematic when there is >1 treatment option for a condition. METHODS AND RESULTS: We used data from the Medicare program to investigate the relationship between institutional volume for open and endovascular abdominal aortic aneurysm (AAA) repair and outcomes, examine trends in volume, and explore the implications for physicians making referrals for AAA repair. Trends in institutional volume were measured for the time period 2001-2006, whereas outcomes were assessed with the use of a previously assembled propensity score-matched cohort covering the time period 2001-2004. Between 2001 and 2006, there were a total of 230 736 repairs of either an intact or ruptured AAA for traditional Medicare beneficiaries. During this time, the proportion of endovascular cases increased from ≈22 in 2001 to >50 of AAA repairs in 2006, but there was little shift in procedure volume to high-volume institutions. For endovascular repair, adjusted mortality by quintile showed a marked decrease between the first and second quintile, with continued smaller decreases over quintiles 3 to 5. For open repair, adjusted mortality showed a steady decrease across the quintiles of volume. CONCLUSIONS: We found a steady increase in survival with increasing volume of open repair but relatively little improvement after reaching a relatively low threshold for endovascular repair. Because hospital experience with one repair method does not translate into improved outcomes for the alternative method, referring clinicians must consider both treatment options when making referral decisions.