Intravascular imaging and functional assessment for coronary in-stent restenosis: Current status and future directions

Despite significant advancements in drug-eluting stent technology, in-stent restenosis (ISR) still occurs in approximately 10 % of patients undergoing percutaneous coronary intervention, remaining a significant global health concern. The mechanisms underlying ISR are complex and multifactorial, yet recent innovations in intravascular imaging and functional assessment have substantially advanced our understanding, enabling more targeted and personalized therapies. This review synthesizes the latest insights into ISR, emphasizing the pivotal roles of advanced imaging modalities, such as optical coherence tomography (OCT) and intravascular ultrasound, and functional assessments like quantitative flow ratio and optical flow ratio in guiding ISR management. Additionally, we explore the clinical implications of in-stent neoatherosclerosis and calcified nodules as key pathological mechanisms influencing restenosis progression and patient outcomes. The review also highlights the significance of OCT-based ISR classifications in refining treatment approaches. By integrating these diagnostic and therapeutic advances, this work provides clinicians and researchers with an updated foundation and actionable insights for optimizing ISR management through tailored, imaging-guided strategies.