Determinants of slow flow following stent implantation in intravascular ultrasound-guided primary percutaneous coronary intervention.

Slow flow is a serious complication in primary percutaneous coronary intervention (PCI) and is associated with poor clinical outcomes. Intravascular ultrasound (IVUS)-guided PCI may improve clinical outcomes after drug-eluting stent implantation. The purpose of this study was to seek the factors of slow flow following stent implantation, including factors related to IVUS-guided primary PCI. The study population consisted of 339 ST-elevation myocardial infarction patients, who underwent stent deployment with IVUS. During PCI, 56 patients (16.5%) had transient or permanent slow flow. Multivariate logistic regression analysis showed age (OR 1.04, 95% CI 1.01-1.07, P = 0.01), low attenuation plaque on IVUS (OR 3.38, 95% CI 1.70-6.72, P = 0.001), initial Thrombolysis In Myocardial Infarction (TIMI) flow grade 2 (vs. TIMI 0: OR 0.44, 95% CI 0.20-0.99, P = 0.046), and the ratio of stent diameter to vessel diameter (per 0.1 increase: OR 2.63, 95% CI 1.84-3.77, P < 0.001) were significantly associated with slow flow. A ratio of stent diameter to vessel diameter of 0.71 had an 80.4% sensitivity and 56.9% specificity to predict slow flow. There was no significant difference in ischemic-driven target vessel revascularization between the modest stent expansion (ratio of stent diameter to vessel diameter <0.71) and aggressive stent expansion (ratio of stent diameter to vessel diameter ≥0.71) strategies. Unlike other variables, the ratio of stent diameter to vessel diameter was the only modifiable factor. The modest stent expansion strategy should be considered to prevent slow flow following stent implantation in IVUS-guided primary PCI.