Introduction to the iFR® Modality
instant wave-free Ratio™
Wave Free Period
- Volcano’s proprietary instantaneous, trans-lesional pressure ratio measured during the wave-free period.
- Assesses lesion significance in about five heartbeats without the need for hyperemic agents.
- The Instantaneous pressure ratio, across a stenosis during the wave-free period, when resistance is naturally constant and minimized in the cardiac cycle.
Change in Pressure = Change in Flow x Constant Resistance
△P = △Q x R
Fundamental Equation for relating Pressure and Flow Derived from Poiseuille’s Law for Fluid Dynamics
- The FFR modality uses hyperemic agents to achieve a state of constant resistance.
- The iFR modality uses a period of the cardiac cycle when resistance is naturally constant.
Wave Free Period
Pressure, Resistance, and Intensity During the Wave Free Period
- Noise from compression and suction waves is minimized.
- Resistance is constant so △P is proportional to △Q (flow).
- Velocity is higher so better power to discriminate.
iFR® Modality with Verrata™ Pressure Guide Wire in Multi-Vessel Disease
Case example from Imperial College, London - February 2014
DownloadsiFR Scout™ Overview ACC/SCAI Recommendation Letter for iFR® CPT Coding The iFR® Modality Fundamentals Hybrid iFR® / FFR Approach and Cut Points ADVISE II Data Sheet
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1. Escaned J. ADVISE II: A Prospective, Registry Evaluation of iFR vs. FFR. TCT 2013. Lecture conducted from San Francisco, CA.
2. Sen S, et al. Development and validation of a new adenosine-independent index of stenosis severity from coronary wave-intensity analysis: results of the ADVISE (ADenosine Vasodilator Independent Stenosis Evaluation) study. J Am Coll Cardiol. 2012 Apr 10;59(15):1392-402.