Abstract 17018: Amputation After Atherectomy: Studying Long-Term Outcomes Using an Instrumental Variable Method

Abstract

Introduction: Outcomes for atherectomy remain poorly characterized. Our objective was to use instrumental variable (IV) analysis to compare long-term amputation rates in patients receiving atherectomy versus other traditional peripheral vascular interventions (PVI) approaches. Methods: We queried the Medicare-linked Vascular Quality Initiative registry for patients undergoing PVI from 2010-2015. The exposure was treatment: atherectomy (+/- balloon angioplasty) versus other PVI types. The primary outcome was amputation. We used the proportion of atherectomy procedures of all PVIs performed at each hospital as an IV and compared the estimates from IV analysis to multivariable Cox regression and propensity-matched estimates. Results: In this cohort of 19693 patients, 2103 (10%) received atherectomy. Compared to patients receiving other PVI, patients receiving atherectomy were more likely to have a femoropopliteal artery (65% vs 48%, p<0.001) treated with worse disease severity (TASC B and greater: 77% vs 69%, p<0.001). The 5-year overall amputation rate was 31% (158 amputations per 1000 patients/year) in patients receiving atherectomy versus 24% (105 amputations per 1000 patients/year) for other PVIs (log-rank p<0.001). Without adjustment, patients undergoing atherectomy were 40% more likely to have an amputation (Figure 1). After adjusting for patient demographics, comorbidities, and disease characteristics, this effect was mitigated to 15% and 16% for multivariable Cox and propensity-matched approaches, respectively. However, after the IV adjusted analysis accounted for unmeasured confounders, patients receiving atherectomy versus non-atherectomy PVI were 78% more likely to have an amputation. Conclusions: Patients receiving atherectomy were more likely to have an amputation. Unmeasured confounders such as selection bias may play an important role in the long-term risk of amputation for patients undergoing atherectomy.