What is Fractional Flow Reserve (FFR) and its diagnostic threshold?

• A. A measure of physiologic significance of a stenosis using maximal hyperemia; abnormal FFR ≤ 0.80 usually indicates ischemia-producing lesion.
• B. A resting index measured without hyperemia.
• C. An imaging modality to visualize plaque morphology.
• D. The rate of blood flow during diastole.

Answer: (A)

FFR is a physiologic measure that tells us whether a coronary stenosis is likely to cause ischemia by comparing the pressure distal to the narrowing with the aortic pressure during maximal hyperemia. When we induce maximal dilation of the coronary microcirculation, resistance is minimized, so the pressure drop across a lesion reflects its potential to limit blood flow under stress. This distal-to-aortic pressure ratio is expressed as a number between 0 and 1; a lower number means a greater pressure drop and a higher chance that the lesion will cause ischemia.

The standard diagnostic threshold is 0.80 or less, which indicates the stenosis is typically hemodynamically significant and may benefit from revascularization. Values above 0.80 suggest the lesion is unlikely to cause ischemia under stress.

FFR is measured with a pressure-sensing guidewire during induced hyperemia (often with adenosine). It is not a resting index, nor an imaging modality, nor a measure of diastolic flow rate.