Reconciling Poststenotic Pressure With Hyperemic Flow
Comparing Coronary Flow Reserve, Instantaneous Wave-Free Ratio, and Fractional Flow Reserve
Vigorous controversy continues in the coronary physiological community about how a basal index of stenosis severity can compete effectively with a hyperemic index1–3 and challenges conventional wisdom and our understanding of what is a true ischemic response that can be quantitated in the catheterization laboratory. Moreover, the controversy is fueled by the absence of an easily obtainable ischemic standard against which various physiological indices of hemodynamic lesion significance can be compared and has led to numerous studies using a noninvasive or surrogate physiological measurement, such as hyperemic stenosis resistance,4,5 or as in the current study, coronary flow reserve (CFR, hyperemic/basal flow velocity ratio) to demonstrate the strengths and weaknesses among the proposed pressure-only indices.
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In this issue of Circulation: Cardiovascular Interventions, Petraco et al6 report their pressure and flow velocity data acquired with sensor angioplasty guide wires across 216 coronary stenoses in 186 patients in the catheterization laboratory. Using CFR as a standard, the basal instantaneous wave-free pressure ratio (iFRbasal) had stronger correlation than fractional flow reserve (FFR) to CFR (correlation coefficient, r=0.68 versus 0.50; P<0.001) and higher agreement (receiver operator curveauc=0.82 versus 0.72; P<0.001 for CFR <2.0). Of note, the hyperemic iFRa performed worse than the iFRbasal (the receiver operator curveauc was 0.74; P<0.001 versus iFRbasal) but similar to FFR. In keeping with the function of a severe stenoses, flow rates across stenoses with FFR <0.75 were reduced and similar for both iFR and FFR (22 versus 26 cm/s; P=ns) in contrast to flow rates for nonsignificant stenoses (ie, FFR >0.75), where flow was higher for the hyperemic index (as it should be) when compared with the iFRbasal (42 versus 26 cm/s; P<0.001). …