Development and Internal Validation of a Bailout Risk Score in PCI with Drug-Coated Balloons

<b>Background/Objectives</b>: Bail-out stenting remains a procedural challenge for percutaneous coronary intervention (PCI) performed with drug-coated balloons (DCBs). No dedicated bedside tool is currently available to predict this event. We aimed to develop and internally validate a bedside Bail-Out Risk Score. <b>Methods</b>: We analyzed patients treated with DCBs between 2021 and 2025. Predictors of bailout stenting were identified through univariate analysis, and variables with <i>p</i> < 0.10 were entered into a multivariable logistic regression model. Regression coefficients were then transformed into integer points using the Sullivan method. Model performance was evaluated by AUC-ROC, calibration, and bootstrap internal validation (B = 1000). <b>Results</b>: A total of 352 patients (399 de novo lesions) were treated with DCB-only PCI. Bail-out stenting occurred in 14.5% of lesions (58/399). Independent predictors of bail-out stenting were prior CABG (OR 4.29, <i>p</i> = 0.002), proximal lesion location (OR 2.99, <i>p</i> = 0.003), and diffuse disease (OR 2.18, <i>p</i> = 0.018). Prior PCI (OR 0.44, <i>p</i> = 0.009) and lipid-lowering therapy (OR 0.42, <i>p</i> = 0.029) were protective, while LAD involvement showed a non-significant trend (OR 1.57, <i>p</i> = 0.137). The model demonstrated moderate discrimination (AUC = 0.734; optimism-corrected AUC = 0.704) and excellent calibration (intercept = 0.000, slope = 1.000). The final score (range -4 to +8) stratified lesions into low (≤-1), intermediate (0-3), and high (≥3) risk groups, with progressively higher predicted probabilities (≤9%, 13-37%, and ≥49%). <b>Conclusions</b>: The Bail-Out Risk Score provides a practical and reliable bedside tool to estimate procedural risk during stentless PCI.