Management of Coronary Stent Underexpansion.

Coronary stent underexpansion is an important problem and limitation of percutaneous coronary intervention, adversely affecting both short- and long-term patient outcomes. Stent underexpansion occurs when a stent fails to expand adequately compared with the adjacent reference segment, resulting in inadequate luminal gain. Multiple studies suggest that stent underexpansion is associated with increased risks of in-stent restenosis, stent thrombosis, and myocardial infarction, resulting in recurrent symptoms, readmissions, repeat interventions, and increased mortality. Contributing factors for stent underexpansion include severe calcification, inadequate lesion preparation, suboptimal stent deployment, and preexisting in-stent restenosis. Calcific plaques, especially when present behind a previously implanted, underexpanded stent, pose a significant challenge for further stent optimization. These lesions are often resistant to high-pressure balloon dilatation and may require advanced techniques that carry increased risks of complications. Intravascular imaging modalities, such as intravascular ultrasound and optical coherence tomography, have emerged as essential tools in diagnosing and managing stent underexpansion. These techniques provide a more detailed evaluation of the vessel and previously implanted stent, enabling the clinician to understand the exact mechanism of stent failure, and assess plaque burden and morphology, which ultimately helps guide appropriate treatment strategies. Despite the clinical importance of stent underexpansion, there is currently no consensus on its optimal treatment, largely because of the absence of large prospective studies in this area. This comprehensive review aims to summarize the existing evidence, clinical experience, and treatment strategies for coronary stent underexpansion, with the goal of providing practical guidance to clinicians to help optimize percutaneous coronary intervention and patient outcomes.