Aims/IntroductionThe coronary physiology and prognosis of patients with different hemoglobin A1c (HbA1c) levels after percutaneous coronary intervention (PCI) are currently unknown. The aim of this study was to assess the effect of different levels of HbA1c control on coronary physiology in patients who underwent PCI for coronary heart disease combined with type 2 diabetes mellitus by quantitative flow ratio (QFR).Materials and MethodsPatients who successfully underwent PCI and completed 1‐year coronary angiographic follow up were enrolled, clinical data were collected, and QFR at immediate and 1‐year follow up after PCI was retrospectively analyzed. A total of 257 patients (361 vessels) were finally enrolled and divided into the hemoglobin A1c (HbA1c)‐compliance group (103 patients, 138 vessels) and non‐HbA1c‐compliance group (154 patients, 223 vessels) according to the HbA1c cut‐off value of 7%. We compared the results of QFR analysis and clinical outcomes between the two groups.ResultsAt 1‐year follow up after PCI, the QFR was significantly higher (0.94 ± 0.07 vs 0.92 ± 0.10, P = 0.019) and declined less (0.014 ± 0.066 vs 0.033 ± 0.095, P = 0.029) in the HbA1c‐compliance group. Meanwhile, the incidence of physiological restenosis was lower in the HbA1c‐compliance group (2.9% vs 8.5%, P = 0.034). Additionally, the target vessel revascularization rate was lower in the HbA1c‐compliance group (6.8% vs 16.9%, P = 0.018). Furthermore, HbA1c ≥7% (OR 2.113, 95% confidence interval 1.081–4.128, P = 0.029) and QFR decline (OR 2.215, 95% confidence interval 1.147–4.277, P = 0.018) were independent risk factors for target vessel revascularization.ConclusionPatients with well‐controlled HbA1c levels have better coronary physiological benefits and the incidence of adverse clinical outcome events might be reduced.