Objectives The ORBIT II (Evaluate the Safety and Efficacy of OAS in Treating Severely Calcified Coronary Lesions) trial evaluated the safety and efficacy of the coronary Orbital Atherectomy System (OAS) to prepare de novo, severely calcified coronary lesions for stent placement.Background Despite advances in interventional techniques, treatment of calcified coronary lesions remains a challenge. Stent placement in these lesions may result in stent underexpansion, malapposition, and procedural complications.Methods ORBIT II is a prospective, multicenter, nonblinded clinical trial that enrolled 443 consecutive patients with severely calcified coronary lesions at 49 U.S. sites from May 25, 2010, to November 26, 2012. Investigators used the centrifugal action of the OAS diamond-coated crown to modify calcified lesions prior to stent placement.Results The pre-procedure mean minimal lumen diameter of 0.5 mm increased to 2.9 mm after the procedure. The primary safety endpoint was 89.6% freedom from 30-day major adverse cardiac events compared with the performance goal of 83%. The primary efficacy endpoint (residual stenosis <50% post-stent without in-hospital major adverse cardiac events) was 88.9% compared with the performance goal of 82%. Stent delivery occurred successfully in 97.7% of cases with <50% stenosis in 98.6% of subjects. Low rates of in-hospital Q-wave myocardial infarction (0.7%), cardiac death (0.2%), and target vessel revascularization (0.7%) were reported.Conclusions The ORBIT II coronary OAS trial met both the primary safety and efficacy endpoints by significant margins. Preparation of severely calcified plaque with the OAS not only helped facilitate stent delivery, but improved both acute and 30-day clinical outcomes compared with the outcomes of historic control subjects in this difficult-to-treat patient population. (Evaluate the Safety and Efficacy of OAS in Treating Severely Calcified Coronary Lesions [ORBIT II]; NCT01092416) (C) 2014 by the American College of Cardiology Foundation