Repeatability of Fractional Flow Reserve Despite Variations in Systemic and Coronary Hemodynamics.

Objectives: This study classified and quantified the variation in fractional flow reserve (FFR) due to fluctuations in systemic and coronary hemodynamics during intravenous adenosine infusion.
Background: Although FFR has become a key invasive tool to guide treatment, questions remain regarding its repeatability and stability during intravenous adenosine infusion because of systemic effects that can alter driving pressure and heart rate.
Methods: We reanalyzed data from the VERIFY (VERification of Instantaneous Wave-Free Ratio and Fractional Flow Reserve for the Assessment of Coronary Artery Stenosis Severity in EverydaY Practice) study, which enrolled consecutive patients who were infused with intravenous adenosine at 140 μg/kg/min and measured FFR twice. Raw phasic pressure tracings from the aorta (Pa) and distal coronary artery (Pd) were transformed into moving averages of Pd/Pa. Visual analysis grouped Pd/Pa curves into patterns of similar response. Quantitative analysis of the Pd/Pa curves identified the "smart minimum" FFR using a novel algorithm, which was compared with human core laboratory analysis.
Results: A total of 190 complete pairs came from 206 patients after exclusions. Visual analysis revealed 3 Pd/Pa patterns: "classic" (sigmoid) in 57%, "humped" (sigmoid with superimposed bumps of varying height) in 39%, and "unusual" (no pattern) in 4%. The Pd/Pa pattern repeated itself in 67% of patient pairs. Despite variability of Pd/Pa during the hyperemic period, the "smart minimum" FFR demonstrated excellent repeatability (bias -0.001, SD 0.018, paired p = 0.93, r(2) = 98.2%, coefficient of variation = 2.5%). Our algorithm produced FFR values not significantly different from human core laboratory analysis (paired p = 0.43 vs. VERIFY; p = 0.34 vs. RESOLVE).
Conclusions: Intravenous adenosine produced 3 general patterns of Pd/Pa response, with associated variability in aortic and coronary pressure and heart rate during the hyperemic period. Nevertheless, FFR - when chosen appropriately - proved to be a highly reproducible value. Therefore, operators can confidently select the "smart minimum" FFR for patient care. Our results suggest that this selection process can be automated, yet comparable to human core laboratory analysis.
(Copyright © 2015 American College of Cardiology Foundation. Published by Elsevier Inc. All rights reserved.)