LAUSR

The slow flow phenomenon is a critical complication during percutaneous coronary intervention (PCI) that leads to poor outcomes. We aimed to evaluate the mechanisms underlying the slow flow phenomenon using intravascular ultrasound (IVUS). We retrospectively analyzed IVUS data from 62 lesions in 58 consecutive patients who experienced the slow flow phenomenon during PCI. IVUS was performed immediately after the development of the slow flow phenomenon to assess its cause. No IVUS-based evidence of mechanical obstruction was categorized as distal embolization. Distal embolization was observed in 46 lesions (74%). The slow flow phenomenon occurred in all these lesions after stent implantation. In addition to distal embolization, three different mechanisms underlying the induction of the slow flow phenomenon due to mechanical obstructions (16 lesions, 26%) were detected on IVUS, namely, medial dissection/hematoma (6 lesions), intimal flap (6 lesions), and thrombus obstruction (4 lesions). Most mechanical obstructions (13 lesions, 81%) could not be identified by angiography alone. In 15/16 lesions (94%) with mechanical obstruction, deteriorated flow improved immediately after balloon dilatation or bail-out stent implantation, although intracoronary vasodilator administration could not reestablish coronary flow. The frequency of mechanical obstruction as the cause of the slow flow phenomenon was relatively high. Given the difficulty in angiographical differentiation, IVUS-guided management of slow flow may be a useful strategy.