Abstract
Fractional flow reserve (FFR) is now accepted as the reference standard to indicate whether a stenosis is likely to be responsible for ischemia. It is generally accepted that a stenosis with an ischemic value of FFR is responsible for symptom and a worse outcome and should be revascularized, whereas lesions with a non-ischemic FFR have a more favorable prognosis and can be treated medically. Furthermore, FFR-guided revascularization strategy has been definitely proven to be better than angiography-guided strategy in pivotal landmark studies. Instantaneous wave free ratio (iFR) is another physiological index which can be obtained at rest without hyperemic stimulation. iFR is conceptually different from FFR, leading to lively scientific debate about this index. In this review article, the concept, differences and similarities of FFR and iFR are reviewed.
