LAUSR

The status of coronary microcirculation determines health‐ related outcomes in patients, despite the presence of coronary artery disease. Multiple measurement methods have been described in the literature. The index of microvascular resistance (IMR) advantages include its reproducibility, not affected by hemodynamic variability or nonsevere epicardial lesions, and the simplicity of the procedure. However, its use in daily practice is infrequent due to the need of using hyperemic drugs, the need for a pressure wire in the coronary artery, and increase procedural costs and time. To overcome these limitations, angiography‐ derived pressure‐wire‐free alternatives to IMR were developed (IMRAngio). Multiple IMRAngio methods have been published to date, using different algorithms to estimate IMR. The diagnostic performance of these methods was published in separate individual publications. There is a need to summarize the evidence regarding the diagnostic performance across all the available IMRAngio methods to better understand the role of IMRAngio in our real practice. Fernandez Peregrina and collaborators present a systematic review and meta‐analysis of the literature. Studies evaluating IMRAngio versus invasive IMR were included. Pooled values of diagnostic performance and pooled receiver operator curve were analyzed. In total, seven studies directly comparing IMRAngio and IMR were finally considered eligible (687 patients with 807 vessels reported). Pooled sensitivity, specificity, positive LR, and negative LR were 82%, 83%, 4.5, and 0.26, respectively, with a pooled accuracy of 83%. Pooled positive predictive value and negative predictive value were 76% and 85%, respectively. Similar results were obtained when analyzing by acute and nonacute coronary syndromes presentation. The authors conclude that IMRAngio shows a good diagnostic performance for the prediction of abnormal IMR. The main strength of this study is the demonstration that the diagnostic performance of IMRAngio remained high across different methods of assessment. Furthermore, IMRAngio diagnostic performance was stable across clinical presentations, whether stable or unstable coronary syndromes. This enhances the opportunity to better understand the physiology of microcirculation in a large spectrum of coronary diseases. A better understanding of coronary circulation can provide important information about prognosis and management. The main limitation of this study is that the pooled estimates belong to different methods of IMRAngio assessment, which can explain the observed heterogeneity across studies. Some of these approaches need specific software and dedicated training and certification. It is unclear in this report if a specific software of method was superior to others and the potential reasons. Demonstrating that a variety of IMRAngio methods has a good performance in predicting invasive IMA is welcome to our daily practice. The most important barriers for assessing IMR are tackled using IMRAngio, including instrumentation of coronary circulation with guide catheters, stronger procedural anticoagulation, coronary wire advancement, increased time, radiation, and contrast use. With the availability of capable software and training on how to optimize the angiogram to be analyzable for IMRAngio, we can acquire very important prognostic and likely treatment‐changing information for patients with microvascular dysfunction.