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Surgeon, Not Institution, Case Volume Is Associated with Limb Outcomes After Lower Extremity Bypass for Critical Limb Ischemia in the Vascular Quality Initiative
Lily E. Johnston, MD MPH, Margaret C. Tracci, MD JD, John A. Kern, MD, Kenneth J. Cherry, MD, Irving L. Kron, MD, Gilbert R. Upchurch, Jr., MD, William P. Robinson, III, MD.
University of Virginia, Charlottesville, VA, USA.

Studies from large administrative databases have demonstrated associations between institutional case volume and outcomes after lower extremity bypass (LEB). Using a national, prospectively collected clinical database, the objective of this study was to determine trends in the utilization of LEB and to determine the effects of both surgeon and institutional volume on outcome after LEB for critical limb ischemia (CLI).
The Vascular Quality Initiative (VQI) was queried to identify all LEB between 2004-2014. Average annual case volume was calculated by dividing an institution or surgeon’s total LEB volume by the number of years they reported to VQI. Institutional and surgeon volumes were analyzed as continuous variables to determine the impact of volume on major adverse cardiac events (MACE), major adverse limb events (MALE), graft patency, and amputation free survival. Hierarchical regression models were used with cases clustered by surgeon and center. Time-dependent outcomes were evaluated with multivariable shared frailty Cox proportional hazards models.
From 2004-2014, 20,828 LEB operations were performed at 164 institutions by 791 surgeons. Average annual institutional volume ranged from 1.0-157.7 LEBs per year, with a median of 25.3 [IQR 14-48.5]. Average annual surgeon volume ranged from 1-57 LEBs per year with a median of 6.25 [IQR 2.5-11]. The median number of bypass operations per surgeon and center did not change appreciably over time; median surgeon and institution volume were 9 and 33.5 in 2004, and 7 and 36.5 in 2014 respectively. Institutional LEB volume was not associated with major adverse cardiac or limb events, nor with loss of patency. However, average annual surgeon volume independently predicted MALE and primary patency. Institutional and surgeon volume did not predict MACE.
In contradistinction to previous studies, there was no relationship in this study between institutional LEB volume and outcomes after LEB for CLI. However, greater average annual surgeon volume was associated with improved primary patency and decreased risk of all adverse limb events. Open LEB remains a safe and effective procedure for limb salvage. Limb-related outcomes in CLI will be optimized if surgeons maintain adequate volume of LEB.

Effects of volume on outcomes. * denotes p<0.05
OutcomeEvent Rate (Overall or at 1 year)Univariate Odds & Hazard Ratios (95% Confidence Intervals)Multivariable Odds & Hazard Ratios (95% Confidence Intervals)
Surgeon volume (per 10 cases)Center volume (per 20 cases)Surgeon volume (per 10 cases)Center volume (per 20 cases)
MACE, in hospital5.1%0.91 (0.82-1.01)0.96 (0.89-1.04)0.96 (0.86-1.07)0.97 (0.90-1.05)
Amputation-free survival78.3%1.03 (0.99-1.07)1.02 (0.97-1.07)1.03 (0.98-1.08)1.01 (0.95-1.07)
MALE, time to event34.5%0.94 (0.90-0.99)*0.99 (0.95-1.03)0.93 (0.88-0.98)*1.01 (0.96-1.06)
Loss of primary patency27.9%0.94 (0.89-0.99)*0.95 (0.90-1.01)0.91 (0.85-0.96)*0.97 (0.91-1.03)
Loss of secondary patency18.7%1.01 (0.95-1.07)0.97 (0.90-1.04)0.96 (0.89-1.04)0.97 (0.90-1.05)

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