Diagnostic Accuracy of Microcatheter Derived Fractional Flow Reserve.

Microcatheter derived fractional flow reserve (FFRMC) system has an increased profile compared with pressure-wire derived fractional flow reserve (FFRW). Consequently, the FFRMC system itself may increase the degree of coronary artery stenosis and lower the measured FFR value. This can affect the diagnostic accuracy of the FFRMC system and inadvertently result in erroneous therapy for patients. Our aim was to evaluate the diagnostic accuracy FFRMC measurements and provide a means for clinicians to interpret individual FFRMC results with respect to FFRW. 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 FFRW value ≤0.80. The mean values for FFRMC and FFRW were 0.80 ± 0.11 and 0.83 ± 0.09, respectively. Bland-Altman analysis demonstrated a bias toward overestimation of FFR by FFRMC (bias, -0.03 [0.05]). The overall lesion level diagnostic accuracy of the FFRMC system was 80.4% (95% confidence interval [CI] 76.2% to 84.0%). The diagnostic accuracy for FFRMC 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 FFRW threshold of ≤0.80, 16.3% of lesions would have had inappropriate revascularization according to FFRMC measurements. Receiver-operating characteristics suggested the optimal cut-off value of FFRMC to determine ischemia was 0.78. In conclusion, the diagnostic accuracy of FFRMC 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.