Baseline Instantaneous Wave-Free Ratio as a Pressure-Only Estimation of Underlying Coronary Flow Reserve

Abstract

Background— Coronary flow reserve has extensive validation as a prognostic marker in coronary disease. Although pressure-only fractional flow reserve (FFR) improves outcomes compared with angiography when guiding percutaneous coronary intervention, it disagrees with coronary flow reserve classification 30% of the time. We evaluated whether baseline instantaneous wave-free ratio (iFR) could provide an improved pressure-only estimation of underlying coronary flow reserve. Methods and Results— Invasive pressure and flow velocity were measured in 216 stenoses from 186 patients with coronary disease. The diagnostic relationship between pressure-only indices (iFR and FFR) and coronary flow velocity reserve (CFVR) was compared using correlation coefficient and the area under the receiver operating characteristic curve. iFR showed a stronger correlation with underlying CFVR (iFR–CFVR, ρ=0.68 versus FFR–CFVR, ρ=0.50; P <0.001). iFR also agreed more closely with CFVR in stenosis classification (iFR area under the receiver operating characteristic curve, 0.82 versus FFR area under the receiver operating characteristic curve, 0.72; P <0.001, for a CFVR of 2). The closer relationship between iFR and CFVR was found for different CFVR cutoffs and was particularly marked in the 0.6 to 0.9 FFR range. Hyperemic FFR flow was similar to baseline iFR flow in functionally significant lesions (FFR ≤0.75; mean FFR flow, 25.8±13.7 cm/s versus mean iFR flow, 21.5±11.7 cm/s; P =0.13). FFR flow was higher than iFR flow in nonsignificant stenoses (FFR >0.75; mean FFR flow, 42.3±22.8 cm/s versus mean iFR flow, 26.1±15.5 cm/s; P <0.001). Conclusions— When compared with FFR, iFR shows stronger correlation and better agreement with CFVR. These results provide physiological evidence that iFR could potentially be used as a functional index of disease severity, independently from its agreement with FFR.

Diagnostic Performance of In‐Procedure Angiography‐Derived Quantitative Flow Reserve Compared to Pressure‐Derived Fractional Flow Reserve: The FAVOR II Europe‐Japan Study

“…Multiple studies presented approaches to avoid hyperemia for physiological lesion assessment, such as instantaneous wave‐free ratio and resting distal pressure/aortic pressure measurements. The resting indices perform similar with an overall diagnostic agreement between 80% and 90% when compared with FFR depending on distribution of lesions included in the studies 20, 21, 22, 23, 24. Still, instantaneous wave‐free ratio–based strategies versus an FFR strategy resulted in comparable clinical outcomes at 1 year in 2 large, randomized clinical trials 23, 24.…”

Instantaneous Wave-free Ratio versus Fractional Flow Reserve to Guide PCI

“…In the JUSTIFY-CFR study (Joined Coronary Pressure and Flow Analysis to Determine Diagnostic Characteristics of Basal and Hyperemic Indices of Functional Lesion Severity-Coronary Flow Reserve), iFR had better agreement with coronary flow reserve than did FFR. 5 Also, FFR was found to be more likely to overestimate lesion severity than iFR, most likely because hyperemia causes a pressure drop below the FFR threshold of 0.80 in lesions of interme- 18,19 Thus, the FFR threshold that was used in our trial may not have been optimal, although it was the threshold used in the FAME (Fractional Flow Reserve Versus Angiography for Multivessel Evaluation) and FAME 2 trials. 2,3 The proportion of evaluated lesions that were hemodynamically important was low in both groups.…”

“…[4][5][6][7] The instantaneous wave-free ratio (iFR) is a recently developed physiological index used to assess the severity of stenosis.The iFR is calculated by measuring the resting pressure gradient across a coronary lesion during the portion of diastole when microvascular resistance is low and stable. 8 Benefits of iFR include the ability to obtain an instantaneous lesion assessment without the need to administer a hyperemic agent, such as adenosine.…”

Use of the Instantaneous Wave-free Ratio or Fractional Flow Reserve in PCI

“…Our trial also provides clinical evidence that there is no significant advantage to the administration of a hyperemic agent -a finding consistent with results of studies in which iFR and FFR were compared with other reference standards. 13,14,19,20 Although evidence supporting the benefits of physiologically guided revascularization has accumulated over the past decade, adoption of this approach in clinical practice has lagged. There are many reasons for this, including equipment and drug costs, inadequate reimbursement, physician preferences, patient symptoms, and addi- …”

“…11 Several studies have questioned the need for the administration of a vasodilator to assess stenosis severity. [12][13][14] In these studies, investigators found that in determining stenosis severity, FFR was not superior to the instantaneous wave-free ratio (iFR), a pressurederived index of stenosis severity that is not obtained with the administration of a vasodilator. We aimed to determine the efficacy and safety of an iFR-guided strategy versus an FFR-guided strategy for coronary revascularization.…”