Clinical Significance of the Difference Between Fractional Flow Reserve and Quantitative Flow Ratio

BACKGROUND: The quantitative flow ratio (QFR), an angiography-based index for the assessment of coronary functional stenosis, correlates well with fractional flow reserve (FFR). In this study we explored the clinical significance of the difference between these values, calculated by subtracting FFR from QFR (delta QFR-FFR), in patients undergoing FFR-guided elective percutaneous coronary intervention (PCI). METHODS AND RESULTS: This retrospective analysis included patients with chronic coronary syndrome who underwent FFR-guided PCI and comprehensive coronary functional assessments, including QFR. Patients were divided into tertiles based on pre-PCI delta QFR-FFR. We compared clinical and physiological characteristics and major adverse cardiovascular events (MACE; a composite of cardiac death, myocardial infarction, stroke, and heart failure requiring admission) among the 3 groups, and evaluated delta QFR-FFR as a predictor of MACE. Among 301 patients, lower delta QFR-FFR was associated with a lower QFR pullback pressure gradient, a higher index of microcirculatory resistance, lower microvascular resistance reserve, and reduced post-PCI coronary flow reserve, whereas post-PCI FFR was similar across tertiles. MACE occurred more frequently in patients with delta QFR-FFR less than -0.060 (log-rank P=0.006). Cox regression analysis identified lower delta QFR-FFR as an independent predictor of MACE. CONCLUSIONS: Pre-PCI delta QFR-FFR correlates with microvascular dysfunction and diffuse disease patterns. A lower delta QFR-FFR predicted an increased risk of MACE after FFR-guided revascularization, highlighting its potential clinical significance as a risk stratification tool.