179 Quantitative Perfusion CMR in ANOCA MPR could provide valuable diagnostic insights and assist in distinguishing ANOCA from healthy controls. Clinical use of MPR Assessing stress MBF and MPR could serve as a non-invasive tool to evaluate ANOCA and identify patients with a compromised stress MBF or diminished MPR. The Women’s Ischemia Syndrome Evaluation (WISE) study was the first show the prognostic value of global MPR in predicting adverse events among women with ANOCA.22 Subsequent studies have supported these findings, highlighting the ability of MPR and stress MBF to predict death and major adverse cardiac events in patients with no-obstructive CAD.34, 35 Further insight into and understanding of the specific risk factors contributing to a reduced stress flow or MPR is beneficial for the implementation of MPR in clinical practice. While our study did not observe an association between MPR and cardiovascular risk factors in ANOCA patients, Zhou et al.34 reported a correlation between age and hypertension with MPR. Moreover, Zhao et al.36 explored QP in type 2 diabetes mellitus patients, and observed reduced stress MBF and MPR, mirroring our findings in ANOCA patients. This suggests a connection between diabetes and ANOCA. Furthermore, Zhao et al.36 performed a multivariate analysis, and found age and female sex to be associated with a decreased MBF. This indicates that older female ANOCA patients with type 2 diabetes might have the most pronounced reductions in stress MBF and/or MPR, making them prime candidates for evaluation using QP CMR. Limitations While our study provides new insight into QP in ANOCA patients, limitations exist. The relatively small sample size restricts statistical power, particularly in multivariate regression analyses and ANOVA, potentially limiting the robustness of our findings. This limitation is further impacted by the inability of a minority of participants to complete the QP-protocol due to undesired effects during adenosine infusion or deviations in the CMR protocol [Supplementary Figure 1]. Sex differences could not be adequately assessed, although our study’s sex distribution aligns with the reported male–female prevalence of ANOCA.37 Additionally, ethical considerations prevented invasive testing of the healthy control group for CMD or vasospasm. However, this group underwent extensive screening to exclude for individuals with impaired renal function and heart diseases using transthoracic echocardiography, ECG, and laboratory tests. Furthermore, inconsistent diagnostic cutoff values of MPR for diagnosing CMD make it challenging to draw firm conclusions.38. Due to the small sample size in the present study, we were unable to contribute new insights regarding the optimal cutoff value for MPR. Also, our study included patients pre-CFT, with approximately 50% diagnosed with an ANOCA endotype according to current criteria. Despite these limitations, our study effectively characterized macro- and microvascular function, highlighting the potential of this technique. 8
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