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Effect of Aging on Fractional Flow Reserve　- Hyperemic Index Fractional Flow Reserve May Not Be Sufficient to Reveal the Whole Picture of Coronary Circulation.

In this issue of the Journal, Jin et al8 uniquely demonstrate the effect of age on FFR by analyzing not only FFR itself, but also a relatively new index, delta-FFR defined as the difference between resting Pd/Pa and FFR. This new index includes very similar information as coronary flow reserve. Based on the relationship between the pressure gradient (PG) and blood flow velocity, which can be expressed as Bernoulli’s equation: PG=fv+Sv2, the coronary PG shows a quadratic relation to flow in the presence of stenosis. Each stenosis has a specific pressure–flow curve, which is determined by its morphological here is a growing body of evidence that increased thickening and stiffness of large arteries and endothelial dysfunction in apparently otherwise healthy older persons, along with the ensuing increase in systolic and pulse pressures that was formerly thought to be part of “normal” aging, precede clinical disease and predict a higher risk for developing clinical atherosclerosis, hypertension, and stroke.1 Structurally, left ventricular hypertrophy, heart failure and atrial fibrillation show dramatically increased incidences with age.2 However, the effect of age on physiological parameters is still not well clarified. Coronary physiology assessed by pressure wire and flow wire is a widely accepted method that enables separate evaluation of epicardial stenosis and microvascular resistance in the clinical setting (Figure).3–6 A previous report demonstrated an inverse relationship between age and fractional flow reserve (FFR) and found that FFR-guided percutaT