Bypass operations require what are termed graftable distal vessels. Vessels that are less than one millimeter are very difficult to sew a graft into and present a great size mismatch when compared to the size of a vein graft. Vein grafts frequently range in size from 4 to 6 mm in diameter. A size mismatch will contribute to sluggish blood flow in the graft and lead to early occlusion, also termed graft failure. Coronary angioplasty and coronary stenting have limitations too.
Lesions occurring at branch points are notoriously difficult to treat.
In other situations the patient might be at a high risk for re-stenosis. In these conditions PTCA may be too risky or not cost-effective. Patients deemed not candidates for CABG or PTCA traditionally have had to rely on medical therapy. These agents include nitrates, beta-blockers and calcium channel blockers. The predicament some patients find themselves in however is that they were being referred for revascularization procedures because they already failed medical therapy.