Diagnostic Accuracy of Microcatheter Derived Fractional Flow Reserve

Microcatheter derived fractional flow reserve (FFR_MC) system has an increased profile compared with pressure-wire derived fractional flow reserve (FFR_W). Consequently, the FFR_MC system itself may increase the degree of coronary artery stenosis and lower the measured FFR value. This can affect the diagnostic accuracy of the FFR_MC system and inadvertently result in erroneous therapy for patients. Our aim was to evaluate the diagnostic accuracy FFR_MC measurements and provide a means for clinicians to interpret individual FFR_MC results with respect to FFR_W. Correlation between FFR measurement techniques was analyzed in this lesion level analysis of 413 patients and 441 lesions from 6 studies. The reference standard to determine physiological significant stenosis was FFR_W value ≤0.80. The mean values for FFR_MC and FFR_W were 0.80 ± 0.11 and 0.83 ± 0.09, respectively. Bland-Altman analysis demonstrated a bias toward overestimation of FFR by FFR_MC (bias, -0.03 [0.05]). The overall lesion level diagnostic accuracy of the FFR_MC system was 80.4% (95% confidence interval [CI] 76.2% to 84.0%). The diagnostic accuracy for FFR_MC values <0.75, 0.75 to 0.85 and >0.85 were 83.7% (95% CI 71.4% to 92.4%), 72.3% (95% CI 59.8% to 75.6%), and 99.2% (95% CI 94.8% to 99.8%), respectively. Using the FFR_W threshold of ≤0.80, 16.3% of lesions would have had inappropriate revascularization according to FFR_MC measurements. Receiver-operating characteristics suggested the optimal cut-off value of FFR_MC to determine ischemia was 0.78. In conclusion, the diagnostic accuracy of FFR_MC varies markedly across the spectrum of disease with marked deterioration for values between 0.75 and 0.85. This may result in clinicians to inadvertently revascularize patients with FFR measurements >0.80.