Implications of different definitions for aortic arch classification provided by contemporary guidelines on thoracic aortic repair

Abstract

Contemporary guidelines on thoracic aortic repair provide inconsistent reporting standards for the definition of aortic arch classification in Types I, II and III. The different reported criteria cannot be used interchangeably, due to a very low level of concordance, and this finding has relevant implications for the comparisons between studies using different classifications, and between different datasets of multicentre trials, which are not consistently analyzed with the same criteria. Also, the reported definitions, which were originally proposed for predicting difficult carotid stenting and therefore were conceived for healthy aortic arches, can be influenced by the pathological derangements of the aortic wall, including aneurysms and dissections. In this respect, the Madhwal’s classification, which is based on the diameter of the left common carotid artery, appears to be the more suitable one for aortic arch classification in patients with thoracic aortic disease because it provides relevant clinical information along with an adequate reproducibility.

Aortic arch classification in Types I, II and III represents an anatomic definition suggested as a reporting standard by different contemporary guidelines on thoracic aortic repair [1, 2]. Notably also, this classification has relevant clinical implications for the management of thoracic aortic disease. In particular, Type III arch, which is characterized by an increased angulation, tortuosity and elongation compared to Types I and II [3], was found to predict proximal endograft failure in patients submitted to thoracic endovascular aortic repair in landing Zone 2 or 3 [4], and to be associated with a high prevalence of Type B aortic dissection [5].

Recent studies showed that, in contrast to a commonly held view, in fact three different classifications of aortic arch types exist [6] (Supplementary Material, Fig. S1), and that the three classifications present a very low level of concordance [3]. These findings have clearly relevant implications for the comparison of data from studies using different classifications, as also for the interpretation of results from multicentre trials in which the data from each participating center are not consistently analyzed with the same criteria [3].

Notably also, the Madhwal’s [7], the MacDonald’s [8] and the Casserly’s [9] definitions (Supplementary Material, Fig. S1), in this order, are progressively more selective for Type III arch identification [3]. Hence, because the clinical relevance of Type III arch was found based on the Madhwal’s classification [4, 5], the choice of a more selective method implies that in a relevant number of patients the Type III arch configuration may remain unnoticed, thus exposing these patients to a disregarded increased clinical risk.

Looking at the contemporary guidelines that address the aortic arch [1, 2], we found that the Society for Vascular Surgery [1] suggests the use of the criteria proposed by Madhwal et al. [7]. According to these, Type III arch is defined as having a distance greater than twice the diameter of the left common carotid artery (LCCA) between the highest point of the arch and the origin of the innominate artery (IA) (Supplementary Material, Fig. S1). The STORAGE guidelines [2], on the contrary, suggest the use of the criteria introduced by Casserly and Yadav [9], according to which Type III arch presents an origin of the IA below the horizontal plane of the inner curvature of the aortic arch. Notably, however, both guidelines report explicative figures in which healthy aortas are depicted, and this is related to the fact that these definitions were initially conceived for predicting a difficult cannulation of the supra-aortic branches during carotid stenting [3].

When applying these two criteria in patients with aortic arch aneurysm or dissection (Fig. 1a and b), however, it becomes apparent that the Casserly’s definition [9] is potentially biased by the dilation of the aorta, which lowers the level of the horizontal plane of the inner curvature of the aortic arch below the origin of the IA (Fig. 1a and b). As a result, the arch can be erroneously classified as a Type I, thus disregarding its hostile geometrical features. On the contrary, the Madhwal’s classification [7], being based on the diameter of the LCCA, is less frequently influenced by the pathological derangements of the aortic wall. In this respect, we previously suggested that, in patients with aortic aneurysm, in the case the origin of the LCCA is involved in the arch dilation, the diameter of the right common carotid can be used conservatively [4]. We also suggested that, in patients with Type B dissections, in the case the extension of the false lumen prevents a clear definition of the top of the arch, the level of the left subclavian artery should be considered conservatively as such [4].

Figure 1:

Lack of concordance between Madhwal’s and Casserly’s definitions in an aneurysmatic Type III arch (A) and in a dissected Type III arch, with an ectatic ascending aorta (B).

Finally, the diameter of the LCCA and the related take-off angles of the supra-aortic branches according to Madhwal et al. [7] may provide relevant information for total endovascular repair of the aortic arch, and particularly on the mechanical stress exerted on the chimneys or the bridging stents, which may affect the sealing [4].

In conclusion, the present inconsistency between the reporting standards suggested by contemporary guidelines [1, 2] represents a relevant clinical issue, which warrants an agreement between the community of experts. The Madhwal’s classification [7] appears to be the more suitable one for aortic arch classification in Types I–III in patients with thoracic aortic disease because it provides relevant clinical information [4, 5] along with an adequate reproducibility (Table 1).

Table 1.

Anatomic criteria and methods for Aortic Arch Classification for thoracic aortic repair (modified from Madhwal et al. [7])

Criteria
Type I arch	The IA originates within a distance of <1 diameter of the LCCA from the horizontal plane of the outer arch curvature (i.e. top of the arch)
Type II arch	The IA originates at a distance within 1 and 2 LCCA diameters from the horizontal plane of the outer arch curvature (i.e. top of the arch)
Type III arch	The IA originates at a distance >2 LCCA diameters from the horizontal plane of the outer curvature (i.e. top of the arch)
Methods	Only thin-cut (1.0 or 1.5 mm) computed tomography angiography of patients with visible origins of the supra-aortic branches should be used
	The diameter of the LCCA should be measured at its origin in axial view
	Multiplanar reconstruction images should be used to create a parasagittal view to visualize the origin of the IA and the horizontal plane of the outer curvature of the aortic arch in one frame
	In the case the origin of the LCCA is involved in the arch dilation, the diameter of the right common carotid should be used conservatively
	In patients with Type B dissections, in the case the extension of the false lumen prevents a clear definition of the top of the arch, the level of the LSA should be considered conservatively as such

IA: innominate artery; LCCA: left common carotid artery; LSA: left subclavian artery.

SUPPLEMENTARY MATERIAL

Supplementary material is available at ICVTS online.

Conflict of interest: none declared.

Reviewer information

Interactive CardioVascular and Thoracic Surgery thanks Roman Gottardi and the other, anonymous reviewer(s) for their contribution to the peer review process of this article.