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Fractional Flow Reserve (FFR)

Summary

Fractional Flow Reserve (FFR) is a physiological index used in interventional cardiology to determine the hemodynamic significance of a coronary artery stenosis. It is defined as the ratio of maximum blood flow in a stenotic artery to normal maximum flow, clinically estimated as the ratio of distal coronary pressure to aortic pressure during maximal hyperemia. FFR values of 0.80 or less are typically used to guide decisions for percutaneous coronary intervention (PCI) or coronary artery bypass grafting.

Definition and Formula

Fractional Flow Reserve (FFR) is calculated under conditions of maximal hyperemia (maximal vasodilation, typically induced using a pharmacological agent such as adenosine) to minimize and stabilize microvascular resistance. Under these conditions, coronary blood flow is assumed to be directly proportional to perfusion pressure.

The formula for FFR is:

$$FFR = \frac{P_d}{P_a}$$

Where: * $P_d$ is the distal coronary pressure measured by a pressure-sensing guidewire placed distal to the stenosis. * $P_a$ is the aortic pressure (mean arterial pressure) measured at the tip of the guiding catheter.

Clinical Interpretation

  • FFR > 0.80: Indicates a hemodynamically non-significant stenosis. Medical therapy is generally preferred over revascularization.
  • FFR ≤ 0.80: Indicates a hemodynamically significant stenosis. Revascularization (such as PCI) is recommended as it has been shown to improve clinical outcomes compared to medical therapy alone (as of 2026-07-19).

Comparison with Computational Alternatives

Traditional FFR measurement requires the insertion of an invasive pressure wire and the administration of hyperemic agents, which can introduce procedural complexity and patient discomfort. Recent advances have introduced wire-free computational alternatives: * FFRangio: Reconstructs a 3D coronary artery model from 2D angiography and applies computational flow simulations to estimate FFR without invasive wires or hyperemic drugs.

Citations

  • Randles A. Physiological Assessment of Coronary Artery Disease. N Engl J Med 2026;395:80-83. NEJMe2602134.pdf
  • Tonino PA, Fearon WF, De Bruyne B, et al. Angiographic versus functional severity of coronary artery stenoses in the FAME study fractional flow reserve versus angiography in multivessel evaluation. J Am Coll Cardiol 2010;55:2816-21.