Rationale and Design of the SMILE Registry: A Comprehensive Approach to Predicting Treatment Outcomes in Mitral Regurgitation

<b>Background</b>: Mitral valve regurgitation (MR) is associated with an impaired prognosis. Due to its frequently asymptomatic presentation, MR often leads to undertreatment, which can delay diagnosis. In addition, the optimal timing and choice of intervention remain unclear. The Significant Mitral Insufficiency Limburg Evaluation (SMILE) registry aims to provide a comprehensive real-world characterisation of patients with moderate-to-severe mitral regurgitation. <b>Methods and Results</b>: The SMILE registry is a multicentre prospective registry initiated in 2020, enrolling all consecutive patients with moderate-to-severe MR from all hospitals in Limburg, the Netherlands. Treatment approaches include surgical, catheter-based, and conservative (medical) options, with decision-making from an expert multidisciplinary team. Data are collected via Castor EDC, ensuring compliance with the General Data Protection Regulation using pseudonymisation. The co-primary endpoints are all-cause mortality and heart failure hospitalisations during the five-year follow-up. Secondary objectives include describing management strategies, characterising disease progression and cardiac remodelling, evaluating associations between baseline clinical and echocardiographic characteristics and long-term outcomes, identifying predictors of treatment success, and assessing longitudinal changes in health-related quality of life. <b>Conclusions</b>: The SMILE registry represents an important step towards improving MR management. Its broad data collection, including conservative care and patient-reported outcomes, provides valuable real-world insights beyond procedure-focused studies. The registry may refine intervention timing and personalise treatment strategies to enhance patient outcomes and improve their quality of life.