The investigators hypothesize that the orbital atherectomy system (OAS), a newer generation atherectomy device, reduces the incidence of microcirculatory compromise as compared to older generation rotational atherectomy (RA) due to differences in the mechanism of athero-ablation.

The presence of heavily calcified coronary lesions necessitates the use of ablative devices that aid in successful percutaneous coronary intervention (PCI). However, atherectomy devices generate microparticles that embolize to the distal coronary microcirculation and may compromise myocardial tissue perfusion.

Two mechanisms that deserve particular attention are the eccentric mounting of the OAS crown and the higher flow rates on the vasodilator flush. Firstly, as opposed to rotational atherectomy where the larger, centrally mounted burr may cause obstruction of flow during the atherectomy, the smaller eccentrically mounted crown in OAS allows continuous perfusion during both atherectomy as well as rest periods. Second, both during rest and atherectomy, the flow rates of vasodilatory flush is higher in OAS compared to RA. Combined, these differences in coronary and vasodilator flush flow could lead to improved perfusion of the distal circulation, particularly during the atherectomy runs when risk of embolization is highest.

The loss of microcirculatory function can be transient, with partial or complete restoration of microcirculatory blood flow, or permanent. As shown in studies of patients with acute coronary syndromes, the loss of microcirculatory function is a critical and independent predictor of myocardial recovery and adverse outcomes. The putative protective effects of OAS on coronary microvasculature may therefore be of major clinical significance and impact.

Inclusion Criteria:

1. Age ≥ 18 years

2. Patient with an indication for PCI including:

   • Angina (stable or unstable),
   • Silent ischemia (a visually estimated target lesion diameter stenosis of ≥70%, a positive non-invasive stress test, or FFR ≤0.80 must be present),
   • Non-ST Segment Elevation Myocardial Infarction (NSTEMI)

3. Patients will undergo cardiac catheterization and possible or definite PCI with intent to stent using any non-investigational metallic drug-eluting stent (DES)

4. Signed written informed consent

5. Heavily calcified (severe)lesions necessitating atherectomy.

Angiographic inclusion criteria:

1. The target lesion must be located in a native coronary artery with visually estimated reference vessel diameter of ≥2.25 mm to ≤4.00 mm.
2. Lesion length between 20 mm and 50mm

Exclusion Criteria:

1. Estimated creatinine clearance <30 ml/min using Cockcroft-Gault equation, unless the patient is on dialysis;
2. ST-elevation Myocardial Infarction (STEMI) within 24 hours of initial time of presentation to the first treating hospital, whether at a transfer facility or the study hospital.
3. PCI within 24 hours preceding the study procedure.
4. Cardiogenic shock (defined as persistent hypotension (systolic blood pressure <90 mm/Hg for more than 30 minutes) or requiring pressors or hemodynamic support, including intra-aortic balloon pump (IABP), at time of procedure.
5. Mobitz II second degree or complete heart block
6. Malignant ventricular arrhythmias requiring treatment
7. Pulmonary edema defined as patient with shortness of breath, evidence of volume overload on physical exam, and crepitations on physical exam (>1/3 of lungs) or radiographic interstitial or alveolar pulmonary edema
8. Subject is intubated.
9. Known left ventricular ejection fraction (LVEF) <35%.
10. Severe valvular disease (e.g. severe mitral regurgitation or severe aortic stenosis)
11. Patient is participating in any other investigational drug or device clinical trial that has not reached its primary endpoint.
12. Women who are pregnant or breastfeeding (women of child-bearing potential must have a negative pregnancy test within one week before treatment).

General Inclusion - MRI Sub-Study

1. Patients with no prior MI/scarring in the subtended myocardial territory.
2. Patients with no contraindication for MRI studies
3. Patients who could safely receive Gadolinium (i.e. estimated glomerular filtration rate (eGFR) >30)

Angiographic Exclusion Criteria:

1. Lesion length <20mm
2. Study target lesion in a bypass graft
3. Ostial right coronary artery (RCA) study target lesion
4. Chronic total occlusion (Thrombolysis In Myocardial Infarction (TIMI) flow 0/1) study target lesion
5. Bifurcation study lesion with a planned dual stent strategy
6. In-stent restenosis study target lesion

General Inclusion - MRI Sub-Study

1. Patients with no prior myocardial infarction (MI)/scarring in the subtended myocardial territory.
2. Patients with no contraindication for Magnetic resonance imaging (MRI) studies
3. Patients who could safely receive Gadolinium (i.e. eGFR>30)

Up to 18 hours post procedure.