Background: ST-segment elevation myocardial infarction (STEMI) patients undergoing percutaneous coronary intervention (PCI) typically require 3 to 5 days of hospitalization. Prolonged length of stay (LOS) significantly impacts healthcare quality, family burden, and resource allocation. This study aimed to identify clinical predictors and explore the effect of pre-discharge functional capacity on prolonged hospitalization in STEMI-PCI patients in Thailand.

Methods: A retrospective observational cohort study was conducted using the Acute Coronary Syndrome registry at the Queen Sirikit Heart Center (June 2021–June 2023). The analysis included 536 STEMI-PCI survivors, categorized into standard LOS (≤ 5 days; n = 379) and prolonged LOS (> 5 days; n = 157) groups. Independent predictors were determined using multiple logistic regression.

Results: The prolonged LOS cohort was significantly older, had a higher proportion of females, presented with greater clinical severity, and experienced more in-hospital complications. Following multivariate adjustment, initial Killip class IV emerged as the strongest independent predictor of prolonged hospitalization (Adjusted OR = 4.73; 95% CI: 2.56–8.74, p < 0.001). Mechanical complications demonstrated a borderline trend for extended stays (p = 0.053). Conversely, higher physical activity capacity, as indicated by higher estimated pre-discharge METs, was significantly associated with a shorter duration of hospitalization.

Conclusion: Initial hemodynamic compromise, notably Killip class IV, is the primary driver of prolonged hospitalization in STEMI patients following PCI. Higher pre-discharge functional capacity correlates with shorter stays, underscoring the vital role of cardiopulmonary reserve and early rehabilitation strategies in optimizing patient recovery.