Importance of measurement site on assessment of lesion-specific ischemia and diagnostic performance by coronary computed tomography Angiography-Derived Fractional Flow Reserve.

Background: Values of fractional flow reserve (FFR) by coronary computed tomography angiography (CTA) decline from the ostium to the terminal vessel, irrespective of stenosis severity. The purpose of this study is to determine if the site of measurement of FFR impacts assessment of ischemia and its diagnostic performance relative to invasive FFR (FFR).

Methods: 1484 patients underwent FFR; 1910 vessels were stratified by stenosis severity (normal; <25%, 25-50%, 50-70%, and >70% stenosis). The rates of positive FFR (≤0.8) were determined by measuring FFR from the terminal vessel and from distal-to-the-lesion. Reclassification rates from positive to negative FFR were calculated. Diagnostic performance of FFR relative to FFR was evaluated in 182 vessels using linear regression, Bland Altman analysis, and receiver operating characteristic (ROC) curves.

Results: Positive FFR was identified in 24.9% of vessels using terminal vessel FFR and 10.1% using FFR distal-to-the-lesion (p ​< ​0.001). FFR obtained distal-to-the-lesion resulted in reclassification of 59.6% of positive terminal FFR to negative FFR. Relative to FFR, there were improvements in specificity (50% to 86%, p ​< ​0.001), diagnostic accuracy (65% to 88%, p ​< ​0.001), positive predictive value (50% to 78%, p ​< ​0.001), and area-under-the-curve (AUC, 0.83 to 0.91, p ​< ​0.001) when FFR was measured distal-to-the-lesion.

Conclusion: FFR values from the terminal vessel should not be used to assess lesion-specific ischemia due to high rates of false positive results. FFR measured distal-to-the-lesion improves the diagnostic performance of FFR relative to FFR, ensures that FFR values are due to lesion-specific ischemia, and could reduce the rate of unnecessary invasive procedures.