What constitutes a hemodynamically significant arterial stenosis?
A stenosis is generally considered significant if the luminal diameter is reduced by 50%, and the systolic pressure gradient is greater than 10 mm Hg across the lesion. A lumen that is diminished by 50% would have a corresponding 75% reduction in cross-sectional area, which would likely reduce flow to a clinically significant level. In patients with claudication and lesions that are equivocal based on the aforementioned criteria, provocative testing may be performed. One may stimulate arterial dilation with a prolonged inflation of a blood pressure cuff above the systolic pressure on the limb proximal to the level of stenosis, a technique called reactive hyperemia. A gradient greater than 20 mm Hg after vasodilation is considered significant. Nitroglycerin can also be used as a pharmacologic vasodilator. One should remember to treat the patient and not the arteriographic or pressure findings. The clinical history is also important in deciding whether a lesion is significant. Treating an entirely asymptomatic lesion is almost never indicated.