Prognostic Value of Murray’s Law–Based Quantitative Flow Ratio in Multi-Arterial Coronary Artery Bypass Grafting

BACKGROUND: The prognostic value of Murray's law-based quantitative flow ratio (μFR) in multi-arterial coronary artery bypass grafting (CABG) remains unclear. OBJECTIVES: This study aims to investigate whether grafting strategies meeting μFR guidance improve mid-term outcomes following multi-arterial CABG. METHODS: This prospective secondary analysis included patients with available μFR analysis, clinical follow-up, and protocol-driven imaging from the ASRAB-Pilot (Different Anti-Spastic Strategy After CABG Using Radial Artery Grafts) trial. Patients were classified into μFR-guidance-met (all coronary lesions with μFR ≤0.80 were revascularized and all lesions with μFR >0.80 were not revascularized) or μFR-guidance-not-met groups. Outcomes included major adverse cardiac events (composite of death, myocardial infarction, stroke, or revascularization) and graft failure (Fitzgibbon grade B/S/O). Stabilized inverse probability weighting was applied to control confounding. RESULTS: Among 141 patients analyzed, 77 (54.6%) met μFR guidance. At a median follow-up of 29.9 (Q1-Q3: 23.4-36.6) months, no significant difference in major adverse cardiac events was observed (μFR-guidance-met group: 16.0% [9.4%-26.5%] vs μFR-guidance-not-met group: 14.5% [7.8%-26.1%]; adjusted HR: 1.12, 95% CI: 0.47-2.66; P = 0.793). Graft-level analysis showed a significantly lower failure rate of arterial grafts with the μFR-guidance-met group (9.4% [n = 25 of 265] vs 34.9% [n = 15 of 43]; adjusted RR: 0.28; 95% CI: 0.16-0.50; P < 0.001) but not venous grafts (18.8% [n = 32 of 170] vs 22.2% [n = 6 of 27]; adjusted RR: 1.50; 95% CI: 0.61-3.68; P = 0.378). CONCLUSIONS: In patients undergoing multi-arterial CABG, grafting strategies meeting μFR guidance were associated with a significantly lower failure rate of arterial grafts but not venous grafts. However, no improvement in mid-term clinical outcomes was observed, and larger trials are warranted in the future (Quantitative Flow Ratio on Radial Artery Graft Outcome After Coronary Artery Bypass Grafting [ASRAB-QUARGO]; NCT05556590).