Table 1. Histological classifications to determine plaque vulnerability.

Classification	Reference	Application	Goal	Features	Stages
American Heart Association classification	Stary 1994; Stary 1995 (62,63)	Histology	Graduate atherosclerosis severity	Isolated macrophages foam cells	Type 1 (initial) lesion
				Mainly intracellular lipid accumulation	Type 2 (fatty streak) lesion
				Type 2 changes & small extracellular lipid pools	Type 3 (intermediate) lesion
				Type 2 changes & core of extracellular lipid	Type 4 (atheroma) lesion
				Lipid core & fibrotic layer, or multiple lipid cores & fibrotic layers or mainly calcific or mainly fibrotic	Type 5 (fibroatheroma) lesion
				Surface defect, hematoma-haemorrhage, thrombus	Type 6 (complicated) lesion
Lovett classification	Lovett 2004 (64)	Histology	Graduate atherosclerosis severity	Definitely stable, e.g., predominantly fibrous, few inflammatory cells, intact cap	Grade 1
				Probably stable, e.g., one feature of instability such as small haemorrhage or inflamed	Grade 2
				Probably unstable, e.g., inflammation, thin cap, and large core but no rupture	Grade 3
				Definitely unstable, e.g., rupture, thrombus, large haemorrhage, thin inflamed cap	Grade 4