Occurrence of Slow Flow/No-Reflow in Primary Percutaneous Coronary Intervention: Predictors, Management, and Outcomes.

Background Slow flow/no-reflow (SF/NR) can undermine effective reperfusion during primary percutaneous coronary intervention (PCI) for ST-segment elevation myocardial infarction (STEMI). Identifying patients at risk before device escalation may enable protocolized microvascular-protection strategies within STEMI systems of care. Objective This study aimed to determine the prevalence of SF/NR in STEMI treated with primary PCI, identify pre-PCI predictors, and assess short-term in-hospital outcomes associated with SF/NR. Methods In a prospective cohort at a high-volume tertiary center, we enrolled 226 consecutive STEMI patients treated between January 1, 2024, and December 31, 2024 (complete-case analysis). SF/NR was defined as final thrombolysis in myocardial infarction (TIMI) flow <3 in the absence of mechanical obstruction. Multivariable logistic regression estimated independent predictors (adjusted odds ratios (aORs) with 95% CIs). Discrimination was assessed using the area under the receiver operating characteristic curve (AUC) with bootstrap optimism correction. In-hospital outcomes included final TIMI 3 flow, ventricular arrhythmia, hemodynamic instability, heart failure, and death. Results SF/NR occurred in 65/226 patients (28.8%). Independent predictors were diabetes mellitus (aOR, 2.05; 95% CI, 1.07-3.91), TIMI thrombus grade 5 (aOR, 3.02; 95% CI, 1.55-5.87), and pre-PCI TIMI 0 flow (aOR, 3.85; 95% CI, 1.53-9.67); symptom-to-balloon time >6 h was not an independent predictor. Model discrimination was fair (AUC, 0.74; 95% CI, 0.67-0.81; optimism-corrected AUC, 0.73). Compared with patients without SF/NR, those with SF/NR had lower final TIMI 3 flow (43.1% vs 82.0%; difference, -38.9 percentage points; 95% CI, -51.0 to -26.8) and higher rates of ventricular arrhythmia (18.5% vs 5.6%; P = 0.004), hemodynamic instability (24.6% vs 8.6%; P = 0.002), heart failure (21.5% vs 9.3%; P = 0.01), and in-hospital mortality (7.7% vs 1.9%; P = 0.04). Conclusions In contemporary primary PCI for STEMI, SF/NR was common and associated more strongly with thrombus burden and absent antegrade flow, along with diabetes, than with delays >6 hours. A simple pre-PCI triad (diabetes, TIMI thrombus grade 5, and TIMI 0 flow) may help flag higher-risk cases and prompt early microvascular-protection measures; external validation is warranted prior to routine adoption.