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Page 4 of 14 Squizzato et al. Vessel Plus 2023;7:16 https://dx.doi.org/10.20517/2574-1209.2023.05

greater angulation and may be associated with a higher incidence of endograft malapposition.

Recently, it has been proposed an integrated classification combining Ishimaru’s zone with the aortic arch
[14]
type, and defining the Modified Arch Landing Areas Nomenclature (MALAN) . The rationale is that
aortic arch landing zones 0, 1, 2 and 3 are located in a curved portion of the aorta, with different grades of
curvature. Each proximal landing zone (PLZ) has a different grade of curvature; for example, zone 0 is
generally the straightest segment of the arch if compared to zones 2 and 3, and therefore, zone 0 TEVAR has
a lower probability of presenting malapposition. According to MALAN classification, landing zones 2/III
and 3/III identify hostile PLZ for TEVAR because of their angulated anatomy, and are associated with a
poor outcome, resulting in a higher incidence of type Ia endoleak, endograft migration and retrograde
[15]
dissection .

[16]
The arch curvature and angle seem to be predictors of stent graft migration, requiring reintervention . The
severity of aortic curvature is also directly related to the tortuosity index of the aorta, which has been
addressed as an independent risk factor for endograft malapposition and the presence of post-operative
[17]
bird-beak [18,19] [Figure 4]. These factors may give us an estimated risk of failure of the endograft, but they do
not represent strict exclusion criteria. To the best of our knowledge, the only strict exclusion criteria is the
aortic diameter since the largest endograft available on the market is 46 mm.

Hemodynamic features
The aortic arch is the most mobile and flexible segment of the aorta, with continuous movements
depending on the cardiac cycle and blood pressure. Stress zones are evident, and this can be a determining
factor for its endovascular treatment, both during endograft deployment (being responsible for inaccurate
positioning, or the windsock effect) and during the long-term follow-up (contributing to endograft
migration, misplacement, and consequent endoleaks).

Aortic arch anatomical configuration plays a direct role in the determination of the displacement forces that
act on thoracic endografts, particularly when the treatment involves a proximal landing zone in zones 0, 1
or 2. In such cases, morphological issues and subsequent considerations about hemodynamic drag forces
become crucial.

The stent graft is constantly exposed to drag forces determined by the cardiac output and this is an essential
key to figure out in the understanding of TEVAR pitfalls. The correct sealing in the PLZ with complete
apposition of the stent graft to the aortic wall is inescapable to gain the long-term efficacy of TEVAR. Stent
graft changes over time together with the aorta and therefore the PLZ.

The displacement forces act in a vectorial way and are orthogonal to the outer curvature of the aortic arch
and therefore to the greater curvature of the endograft, leading to continuous cranial oriented stress force in
the arch and in a sideway direction in the first portion of the descending aorta .
[20]
Drag forces act in a three-dimensional configuration and have variable magnitudes in different zones of the
[21]
thoracic aorta, influenced by angulation and tortuosity, with higher values in zone 3 .
The combination of the anatomical aspects and fluid dynamics appears to be the key to a better
understanding of the mechanism that leads to the long-term failure of TEVAR.