Murray law-based quantitative flow ratio versus invasive fractional flow reserve in the left anterior descending coronary artery: impact of hydrostatic pressure correction and clinical implications

Background Invasive fractional flow reserve (FFR) is the gold standard for guiding coronary revascularization. Angiography-derived FFR techniques such as the quantitative flow ratio (QFR) provide a less invasive alternative. Prior studies generally demonstrated good agreement between QFR and FFR, but the effect of hydrostatic pressure differences has not been quantitated as a potential source of systematic discrepancy. We investigated whether correcting invasive FFR for hydrostatic pressure error improved its agreement with QFR in the left anterior descending artery (LAD) lesions. Methods We studied 33 coronary lesions in the LAD. Invasive FFR was measured using the standard pressure-wire technique under hyperemia. Murray law-based QFR (μQFR) was computed from invasive coronary angiography. The vertical height difference between the coronary ostium and the distal sensor position was measured on coronary angiographic images from a lateral view, and the hydrostatic pressure offset was added to the distal pressure reading. FFR was recalculated with this hydrostatic correction. We compared uncorrected FFR and hydrostatic pressure-corrected FFR against μQFR. Results Hydrostatic correction increased the mean FFR from 0.78 ± 0.11 to 0.81 ± 0.10 ( p < 0.0001), virtually matching the mean μQFR (0.81 ± 0.10). The Pearson correlation between μQFR and FFR was high both before and after correction ( r = 0.95, p < 0.0001). However, Bland–Altman analysis showed that correcting the hydrostatic error eliminated the small bias between FFR and μQFR (mean difference bias improved from +0.03 to 0.00). By ROC analysis, an uncorrected FFR <0.80 was best predicted by μQFR <0.84 [area under the curve (AUC) 0.976], whereas using hydrostatic pressure-corrected FFR <0.80 corresponded to a μQFR threshold <0.78 (AUC 0.977). Conclusions Correcting FFR for hydrostatic pressure improved its agreement with μQFR, suggesting that accounting for this error may enhance the consistency of physiologic lesion assessments.