A Poiseuille-based coronary angiographic index for prediction of fractional flow reserve.

BACKGROUND: Coronary revascularization is commonly based on the angiographic finding of percent diameter stenosis (%DS) >50 while lesion length (LL), which contributes to flow-limitation according to Poiseuille's equation, is disregarded. Fractional flow reserve (FFR) is superior to assessment of %DS for identifying flow-limiting lesions, but the technology is invasive and relatively expensive. We developed a Poiseuille-based angiographic index, incorporating both minimal lumen diameter (MLD) and LL, for improved assessment of the hemodynamic significance of intermediate coronary lesions. The present study was designed to test the hypothesis that the Poiseuille-based angiographic index correlated better with FFR measurements than angiographic assessment of %DS.
METHODS: We performed quantitative coronary angiography (QCA) and FFR measurements in 46 intermediate coronary lesions in 41 symptomatic patients referred for diagnostic coronary angiography. From QCA we determined LL, MLD and %DS and calculated an angiographic index, the LL/MLD(4) ratio.
RESULTS: Mean LL was 14.2 ± 7.8 (range: 4.3-38.8) mm, MLD 1.4 ± 0.4 (range: 0.6-2.3) mm, %DS 46 ± 12 (range: 25-74) and FFR 0.85 ± 0.09 (range: 0.55-1.00). Fractional flow reserve correlated inversely with %DS (R=-0.39, p=0.008) and with the LL/MLD(4) ratio (R=-0.66, p<0.0001). An FFR cut-off value of 0.80 corresponded with a LL/MLD(4) ratio of 12 (p=0.003) but not with a %DS of 50 (p=NS). A LL/MLD(4) ratio ≤ 12 had a specificity of 94% and negative predictive value of 82% for excluding hemodynamically significant lesions with FFR (≥ 0.80).
CONCLUSIONS: The LL/MLD(4) ratio was superior to standard angiographic measurement of %DS for exclusion of hemodynamically significant coronary lesions.