A 68-year-old man with hypertension, smoking history, and hyperlipidemia presents with a 2-hour history of transient monocular blindness (amaurosis fugax) in the left eye. Duplex ultrasound of the left carotid artery shows a heterogeneous atherosclerotic plaque at the bifurcation with the parameter marked **B** (Peak Systolic Velocity) measured at 245 cm/s. Which of the following best describes the hemodynamic significance of this finding and its clinical implication?