**2. Definition and terminology of vulnerable plaque**

The term "vulnerable plaque" has been established as a nomenclature to describe the instability of the plaque at a high risk of disruption, leading to thrombosis and rapid stenosis progression [2–4]. Retrospective autopsy studies reported that the most common histopathological finding associated with plaque rupture was thin-cap fibroatheroma (TCFA), which accounted for 55–60%, in 30–35% plaque erosion and in 2–7% calcified nodule [5]. However, it should be noted that not all TCFAs will rupture, nor will all ruptures lead to a cardiac event [3], but disruption and healing is the mechanism of plaque growth [6] and high-grade stenosis [7]. Consequently, the term "vulnerable patient" has been introduced to indicate the patient who has a high likelihood to develop cardiac events. It remains to be investigated whether we should identify and treat these kinds of vulnerable lesions or patients by coronary intervention before inducing clinical events.
