Murray Law-Based Quantitative Flow Ratio Proficiency in Clinical Practice: Validating Routine Diagnostic Performance and Analyzing Learning Curve Thresholds.

BACKGROUND: Although second-generation Murray law-based quantitative flow ratio uses artificial intelligence-driven automation to improve angiography-derived physiological assessment, the impact of operator learning curves on its diagnostic reliability in routine practice remains unclear. METHODS: Consecutive patients with suspected myocardial ischemia (May 2021 to July 2024) underwent online Murray law-based quantitative flow ratio computation from angiographic images, followed by fractional flow reserve measurement. Diagnostic accuracy was evaluated using receiver operating characteristic analysis. The number of vessels needed to achieve high performance (area under the curve [AUC] ≥0.90) was determined. Learning curves were assessed by sequentially expanding the data set starting from the first 11 vessels. First-order AUC differences (ΔAUCn+1=AUCn+1-AUCn) were calculated to assess the stabilization of diagnostic performance, where AUCn represents the area under the curve after analyzing the first n vessels. RESULTS: Murray law-based quantitative flow ratio showed excellent diagnostic accuracy: Vessel-level AUC was 0.92 (95% CI, 0.89-0.94), and patient-level AUC was 0.91 (95% CI, 0.88-0.94). An AUC ≥0.90 was achieved after analyzing 170 vessels, with continued improvement thereafter. Peak performance and stability were reached at 441 vessels, where incremental ΔAUC values showed no significant deviation from 0 (Mann-Whitney U test, P>0.05). CONCLUSIONS: Operator experience significantly affects Murray law-based quantitative flow ratio accuracy. Analyzing at least 170 vessels ensures high reliability, with optimal performance achieved around 441 cases. Structured training is essential for integrating artificial intelligence-enhanced coronary physiology tools into clinical practice.