In this case, we performed a functional assessment of fixed stenosis and MB by FFR, dFFR, ΔFFR, and ΔdFFR. The “FFR ≤ 0.80” and “ΔFFR ≥ 0.2 (1-0.8)” were used as the cut-off value for ischemia due to fixed stenosis [10]. The “dFFR ≤ 0.76” and “ΔdFFR ≥ 0.24 (1-0.76) " are the cut-off value for functional evaluation of MB [12]. Before stent implantation, ΔFFR1 value was 0.10(< 0.20), and ΔdFFR1 value was 0.15(< 0.24), indicating that neither fixed stenosis nor MB was sufficient to cause myocardial ischemia. However, FFRa3=0.77 and dFFRa3=0.70 indicated distal myocardial ischemia in the LAD. Combined with the patient’s typical angina symptoms and functional evaluation results, a stent was implanted to the fixed stenosis. After stent implantation, the FFRb3 value was 0.89 and the dFFRb3 was 0.86. Nearly half a year follow-up, the patient’s clinical symptoms improved significantly.

Currently, there is no uniform clinical guidance for the treatment of MB. It is mainly based on case reports and expert opinion and also involves decisions made by individual clinicians [11]. For symptomatic MB patients, β-blockers and non-dihydropyridine calcium channel blockers are routinely used as first-line medical therapy. For patients who cannot tolerate β-blockers and calcium channel blockers, ivabradine is a second-line option for pharmacotherapy [13]. For patients with refractory symptoms, invasive treatment strategies such as percutaneous coronary intervention and cardiac surgery may be considered [10]. However, percutaneous coronary intervention within MB has limited efficacy in addressing ischemic symptoms. In addition, there is a high risk of early in-stent restenosis, target vessel revascularization, stent fracture, perforation, and thrombosis [14, 15]. Additionally, cardiac surgeries, including coronary artery bypass grafting (CABG) and supra-arterial myotomy, appear to be more effective than percutaneous coronary intervention. Nevertheless, these procedures still face the risks of surgical trauma, graft occlusion, necrosis, and a higher late recurrence rate of angina [16, 17].

In this case, the patient had multiple consultations at different hospitals and was treated with β-blockers without symptom improvement. Based on the FFR, dFFR, ΔFFR, and ΔdFFR assessment results, a stent was implanted at the proximal fixed stenosis, resulting in a good prognosis and avoiding the risks associated with invasive treatment of MB. For patients with refractory symptoms, functional assessment is necessary when fixed stenosis is encountered with MB. It is noteworthy that ΔFFR and ΔdFFR can further clarify whether ischemia originates from MB, fixed stenosis, or their synergistic effect, thereby better informing clinical strategies. However, invasive FFR assessment faces challenges such as high economic costs, long procedural times, and adverse drug reactions.