Introduction: Fractional flow reserve (FFR)-guided percutaneous coronary intervention improves clinical outcomes compared to angiographic-guided methods. However, hyperemic agents increase procedural time, have undesirable side effects, and impact coronary microvasculature. These issues prompted the study of instantaneous wave-free ratio (iFR), a vasodilator-free index of coronary stenosis. iFR represents the pressure gradient during end-diastole when coronary flow is greatest and distal resistance is lowest. The current meta-analysis examines the diagnostic accuracy of iFR compared to FFR in identifying hemodynamically significant stenoses.
Methods: We searched the databases PubMed, EMBASE, Central, ProQuest, and Web of Science for full text articles published through May 2017 addressing the diagnostic value of iFR referenced to FFR using the keywords “instantaneous wave-free ratio” or “iFR” and “fractional flow reserve” or “FFR.” We performed a pooled analysis to synthesize the diagnostic accuracy, sensitivity, specificity, positive likelihood ratio (LR+), negative likelihood ratio (LR-), positive predictive value (PPV), and negative predictive value (NPV) of iFR compared to the FFR cutoff < 0.8. Overall test performance was summarized with the area under the summary receiver operating characteristic curve (AUC).
Results: Seventeen studies met inclusion criteria with total of 6095 lesions. The pooled diagnostic accuracy of iFR to FFR < 0.8 was 81.4% (95% confidence interval: 78.5% to 84.3%). The sensitivity and specificity were 78.2% (73.3% to 83.1%) and 82.6% (78.6% to 86.6%), respectively. The AUC was 0.86 (0.84-0.88). Comprehensive test results are described in table 1.
Conclusions: iFR shows consistent correlation with FFR as a resting index of coronary stenosis severity without the undesired effects and cost of hyperemic agents. The optimal use of iFR as a hemodynamic measure needs to be examined further in randomized clinical trials.