Performance of the STS Risk Score in Predicting Outcomes in Impella-Supported High-Risk Percutaneous Coronary Intervention: Insights From the PROTECT III Study.

Background: Patients undergoing high-risk percutaneous coronary intervention (HRPCI) with Impella often present with similar or worse anatomical complexity than surgical revascularization candidates, yet the performance of surgical risk models in this setting is unknown. We evaluated Society of Thoracic Surgeons (STS) score performance in predicting outcomes in the PROTECT III study. Methods: PROTECT III enrolled 1237 patients undergoing elective or urgent HRPCI with Impella support from March 2017 to March 2020. Patients were stratified into low (STS <4), intermediate (≥4 to ≤8), and high (>8) risk categories. Primary endpoints were 30-day major adverse cardiovascular and cerebrovascular events (MACCE) and mortality. Model discrimination was evaluated with receiver operating characteristic analysis; calibration was assessed with observed-to-expected (O/E) ratios and Hosmer-Lemeshow testing. Secondary endpoints included 90-day MACCE and 1-year mortality. Results: Of 1237 patients, 728 patients were low-risk, 316 intermediate, and 193 high-risk based on STS score. Higher STS risk was associated with a higher number of comorbidities and more left main and multivessel disease. At 30 days, MACCE rose with risk (low 5.1%, intermediate 10.1%, high 17.6%; Conclusions: The STS score provides reasonable discrimination in Impella-supported HRPCI but poorly predicts event rates, particularly underestimating mortality. These results underscore the need for modification of existing models and validation of HRPCI-specific tools.