The reasons why fractional flow reserve and instantaneous wave-free ratio are similar using wave separation analysis

Figures

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  Fig. 1. Changes in pressures before and after Hyperemia and wave free period extraction through WIA analysis. a Aortic and distal pressures (Pa, Pd), forward and backward waves (Pfor, Pback) in a cycle at pre-hyperemia and hyperemia, and horizontal lines are their average values over a cycle. Pa decreased little but Pd decreased more at hyperemia. Although overall Pback decreases a lot at hyperemia, there is little change in Pfor between pre-hyperemia and hyperemia. b Wave free period was extracted through wave intensity analysis (WIA) as shown in green boxes

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  Fig. 2. Schematic diagram of the process of calculating reconstructed FFR and iFR. Measure Pa, Pd, Ud, divide Pd by Ud, calculate Zi, and find Zc through frequency analysis of Zi. Pback is calculated through WSA. Reconstructed FFR and iFR are calculated by the same formula using trans-stenotic forward pressure at hyperemia and rest conditions, respectively

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  Fig. 3. An in vitro coronary circulation system. Three conditions were created as (a–c). a Basal condition, in which both forward and backward flows existed. Resister was used to control the ratio of forward and backward flow, and the pressure and blood flow were stabilized using the Windkessel model. b Only forward condition, in which backward flow was blocked. By adjusting the height of the reservoir, the Pstatic was controlled. High Pstatic is assumed to be pre-hyperemia and low Pstatic is assumed to be hyperemia. c Only backward flow condition, in which forward flow was blocked for measuring

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  Fig. 4. Pd/Pa in Case1 and 2 at 3 stenosis when Pstatic was 30 and 10 mmHg. When the static pressure was 30 mmHg(High hydrostatic pressure), Pd/Pa in case 2 was set as reconstructed iFR, and when the static pressure was 10 mmHg(Low hydrostatic pressure), Pd/Pa in case 2 was set as reconstructed FFR

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  Fig. 5. The waveform of Pwedge and Pback. The static pressure was a 10 and b 30 mmHg at stenosis 48%. Each static pressure was added to Pback

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  Fig. 6. The correlation between observed wedge pressure (Pwedge) and calculated wedge pressure Pback + Pstatic. The correlation was high (r = 0.990, p < 0.0001) and slope was 1.0612

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  Fig. 7. Correlation between a FFR and reconstructed FFR, b iFR and reconstructed iFR. Both graphs show a high correlation