Poor concordance between definitions of Type III arch and implications on risk prediction and assessment for Carotid Artery Stenting

Type III arch configuration is inconsistently reported as a stroke risk factor during carotid artery stenting (CAS). However, at least three different methods for the definition of Type III arch can be identified from the literature, as related to the level of origin of the innominate artery (IA). According to Casserly's, a Type III arch presents an origin of the IA below the horizontal plane of the inner curvature. According to Madhwal's, a Type III arch has a distance greater than twice the diameter of the left common carotid artery between the highest point of the arch and the origin of the IA. According to MacDonald's, a Type III arch presents a distance of ≥2 cm between the highest point of the arch and the origin of the IA. Our aim was to assess the level of concordance between these different methods.