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Functional coronary angiography (FCA) is a novel modality for assessing the physiology of coronary lesions, going beyond anatomical visualization by traditional coronary angiography. FCA incorporates indices like fractional flow reserve (FFR) and instantaneous wave-free ratio (IFR), which utilize pressure measurements across coronary stenoses to evaluate hemodynamic impacts and to guide revascularization strategies. In this review, we present traditional and evolving modalities and uses of FCA. We will also evaluate the existing evidence and discuss the applicability of FCA in various clinical scenarios. Finally, we provide insight into emerging evidence, current challenges, and future directions in FCA. Plain Language Summary Functional coronary angiography is a technique that combines detailed imaging of the coronary arteries with assessments of how well they function, helping physicians evaluate both large and small arteries in the heart. Unlike traditional angiography, functional coronary angiography uses advanced methods to measure the impact of any abnormalities, without needing extra invasive procedures. This approach is especially useful for patients who have cardiac symptoms but don't show significant blockages on standard tests. Functional coronary angiography is increasingly used to guide treatment decisions, ensuring patients receive the right care while avoiding unnecessary interventions. Functional Coronary Assessment primarily enhances coronary artery disease management by integrating various techniques to measure the hemodynamic significance of coronary lesions, guiding treatment decisions, and improving outcomes. The gold-standard Fractional Flow Reserve, along with alternatives like instantaneous wave-free ratio, resting-full cycle ratio, and diastolic pressure ratio, provides precise lesion severity assessments, reducing unnecessary interventions and enabling tailored revascularization strategies. Emerging technologies like Ultrasound-based fractional flow reserve and Optical Flow Ratio (OFR) offer promising, less invasive alternatives, while tools such as Coronary Flow Reserve and Index of Microvascular Resistance expand FCA's diagnostic scope to microvascular dysfunction and ischemia without obstructive coronary artery disease. FCA also plays a key role in personalized revascularization strategies, from routine management to high-risk, improving clinical decisions, reducing adverse events, and enhancing survival across diverse patient groups. In this review, we present traditional and evolving uses of functional coronary angiography by evaluating its broad applicability across a variety of clinical indications. Article highlights Functional Coronary Angiography (FCA) addresses the limitations of traditional coronary angiography by determining the hemodynamic significance of coronary lesions, guiding management decisions, and improving patient outcomes. Fractional Flow Reserve (FFR) is the gold standard but other measures are being explored. FFR uses invasive pressure measurements under hyperemic conditions to assess lesion severity. Studies like DEFER and FAME have shown that revascularization based on FFR significantly improves outcomes and reduces unnecessary interventions, though it remains underutilized due to procedural complexity. Instantaneous Wave-free Ratio (IFR) offers an alternative to FFR by eliminating the need for a hyperemic agent. Studies show IFR is non-inferior to FFR but brings similar procedural challenges. While less invasive, IFR has shown mixed results, with some evidence of higher long-term mortality. Resting Full-Cycle Ratio (RFR) is another non-hyperemic method that simplifies measurements by avoiding specific timing requirements. RFR has been validated against IFR but shows some discordance with FFR, leading to the suggestion that FFR be used when RFR values are in an intermediate range. Diastolic Pressure Ratio (dPR), like RFR, is a non-hyperemic functional assessment. While validated against IFR and FFR, and shown to predict outcomes in deferred interventions, dPR has less supporting data and is not yet recommended in clinical guidelines. Ultrasonic Flow Ratio (UFR) uses Intravascular Ultrasound (IVUS) for FFR analog calculations, avoiding pressure wires or adenosine. It has strong correlation with and good accuracy in predicting FFR <0.8. It is promising but requires expensive equipment and hasn't been evaluated for clinical outcomes. Optical Flow Ratio (OFR) uses Optical Coherence Tomography (OCT) to calculate an FFR analog without pressure wires or hyperemic agents. It also correlates well with FFR. Coronary Flow Reserve (CFR) measures coronary blood flow at rest vs. hyperemia and quantifies the ability to augment coronary blood flow. Abnormal CFR (<2–2.5) is linked to higher risks of mortality and Major Adverse Cardiovascular Event (MACE). Index of Microcirculatory Resistance (IMR) assesses microvascular function using coronary thermodilution and pressure measurement. FCA has various uses for distinct clinical scenarios. In myocardial bridging, coronary arteries travel inside the myocardium, affecting blood flow. FCA methods like FFR help in managing hemodynamically significant cases with medical or procedural interventions. FFR-guided Coronary Artery Bypass Grafting (CABG) has shown mixed results regarding graft occlusion rates and clinical outcomes. Post-operative Coronary Computed Tomography Angiography (CCTA) and Invasive Coronary Angiography (ICA) assessments remain important for evaluating graft patency and stenoses in native arteries. FCA tools (CFR, IMR, FFR) are critical in diagnosing microvascular dysfunction, especially in cases of ischemia without obstructive Coronary Artery Disease (CAD) (INOCA). Tailored medical therapy based on FCA improves outcomes, particularly in microvascular angina cases. Complete revascularization of all hemodynamically significant lesions during ST-Elevation Myocardial Infarction (STEMI), based on FFR measurements, reduces MACE rates. However, during cardiogenic shock, culprit-lesion-only intervention is preferred due to better survival outcomes. [ABSTRACT FROM AUTHOR] |
