Diagnostic performance of quantitative flow ratio against intravascular ultrasound in left main coronary artery disease: a prospective single-centre study.

Accurate assessment of left main coronary artery (LMCA) disease is essential for guiding revascularization. Intravascular ultrasound (IVUS) is the reference standard for anatomical evaluation of intermediate LMCA stenosis, whereas quantitative flow ratio (QFR) is an angiography-derived, wire-free physiological index. Data comparing these modalities in LMCA disease remain limited. This prospective single-center study included 135 patients with LMCA lesions undergoing coronary angiography and IVUS between January 2024 and June 2025. Offline QFR was calculated using QAngio XA 3D. Significant LMCA disease was defined as IVUS-derived minimum lumen area (MLA) < 6 mm² or QFR < 0.80. Agreement, correlation, and diagnostic performance of QFR were evaluated against IVUS. The mean age was 63.4 ± 9.7 years, and 88.1% were male. IVUS identified significant LMCA disease in 92 patients (68.1%) versus 50 (37.0%) by QFR. Agreement was moderate (κ = 0.426, 95% CI 0.197-0.656; p = 0.0003). Using IVUS as the reference, QFR showed 54.3% sensitivity and 100% specificity. QFR correlated moderately with IVUS-derived MLA (r = - 0.416, p < 0.001) but consistently underestimated vessel dimensions (all p < 0.001). On multivariable analysis, QFR < 0.80 (OR 3.52, 95% CI 1.07-11.57; p = 0.039) and distal LMCA bifurcation lesions (OR 2.41, 95% CI 1.03-5.64; p = 0.043) independently predicted IVUS-defined significant disease. QFR demonstrated moderate concordance with IVUS but limited sensitivity, particularly in distal bifurcation lesions, and underestimated vessel dimensions. These findings limit its utility for LMCA procedural planning and stent optimization, highlighting the need for larger multicenter prospective studies.