Effect of lesion length on fractional flow reserve in intermediate coronary lesions

Background: Fractional flow reserve (FFR) has become a gold standard in physiological assessment of coronary artery stenosis. An FFR <0.75 is considered as a reliable physiological parameter indicating functionally significant lesion. Lesion length (LL) may affect the translesional hemodynamics. However, the effect of LL on FFR has not been adequately assessed. We sought to evaluate the effect of LL on FFR in patients with angiographically intermediate coronary artery disease. Methods: We performed FFR measurements by pressure guidewire in 63 intermediate-grade lesions (63 patients) by visual assessment. Lesion length and percent diameter stenosis (%DS) at the lesion site were determined by performing off-line quantitative coronary angiography analysis. Results: Overall, there was a moderate inverse correlation between FFR and %DS (r = -0.55, P < .001). In addition, there was a weak inverse correlation between LL and FFR (r = -0.31, P < .001). Using a receiver operating characteristic curve analysis, an LL ≥10 mm was identified as the best cutoff value for predicting an FFR <0.75 (sensitivity 95%, specificity 66%, positive predictive power 48%, and negative predictive power 97%). The correlation between FFR and %DS was significantly improved for LL ≥10 mm, as compared with LL <10 mm (r = -0.78, P < .001; r = 0.16, P = NS; respectively). Similar improvement with LL was also observed for intermediate lesions by quantitative coronary angiography (%DS 50%-70%; r = 0.19, P = NS for LL <10 mm; r = -0.74, P < .001 for LL ≥10 mm). Conclusions: This study demonstrates that LL differentially affects the correlation between the functional assessment (FFR) and the "anatomic" severity (%DS) of coronary lesions and suggests that LL has a significant impact on the physiological significance of intermediate-grade coronary lesions.