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.