Intracoronary physiological indices for coronary microvascular dysfunction: from concept to clinical application.

The coronary microcirculation has long been considered a "black box" due to the difficulty of its direct assessment. Abnormalities in this compartment, termed coronary microvascular dysfunction (CMD), are now recognized as important contributors to myocardial ischemia and are increasingly implicated across a wide range of cardiovascular diseases, underscoring the need for precise diagnosis and targeted treatment. Over the past two decades, invasive physiological assessments (IPA) performed during coronary catheterization have been developed to evaluate coronary microcirculation and provide a unique opportunity to assess patient-specific pathophysiology of CMD. IPA is now expected to play a pivotal role not only in the diagnosis of CMD, but also in risk stratification and the development of tailored therapeutic strategies. This article provides an overview of currently available intracoronary physiological indices, summarizing their clinical applications, strengths, and limitations.