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Squizzato et al. Vessel Plus 2023;7:16 https://dx.doi.org/10.20517/2574-1209.2023.05 Page 5 of 14

Figure 4. Aortic tortuosity index (TI) value is obtained by dividing the interested aortic length measured at center line by the geometric
length (A/B= TI) (I). Radius of curvature is an approximative measure of aortic arch curvature. The higher the “r” value, the less curved
the arch can be considered (II). Aortic arch angle is calculated at the highest point of the aortic arch between a line toward a mid-
arterial point in the ascending aorta and one in the descending at the level of pulmonary artery bifurcation (III).

Displacement forces have been found to be higher in zone 0 than in other arch zones. However, TEVAR
performed at this level has lower endoleaks and migration rate compared to other PLZ and this could be
explained by a lower tortuosity and angulation and the chance to obtain a longer PLZ securing a more stable
proximal fixation and sealing of the endograft . The unfavorable hemodynamic asset of the ascending
[22]
aorta seems to be compensated by a more reliable and regular anatomic configuration, suggesting the
decisive role of PLZ.

According to the MALAN classification, zone 3/II and 3/III have also shown the presence of relevant
displacement forces with an orthogonal vector to the aortic longitudinal axis comparable to the one found
in the ascending aorta. Instead of zone 0, proximal landing areas in zones 3/II and 3/III are characterized by
significant angulation and tortuosity that should need an adequately long PLZ to ensure effective and long-
lasting sealing . Zone 3 in angulated aortic arch type II and III seems unfavorable for a standard TEVAR
[23]
procedure with a commonly accepted 20 mm sealing zone length. The presence of the left subclavian artery
limits the applicability of a standard TEVAR and requires the use of scalloped/branched devices or a
carotid-subclavian bypass. In elective cases, it is advisable to preserve the left subclavian artery to prevent
spinal cord ischemia; additionally it is raccomended suspending dual antiplatelet therapy to allow spinal
drainage if signs of ischemia occur. Intra-operative heparinization is mandatory with active clotting time to
be monitored (target > 250 s). Post-operative single antiplatelet is recommended.

ENDOGRAFT CHARACTERISTICS
The progressive improvements in the results of endovascular procedures are directly related to the growing
experience of the physicians and continued improvement in the materials. Research and development of
new endograft and ancillary components are central. In TEVAR, the continuous research of the ideal
endograft is an ongoing process, with the aim to achieve excellent conformability to aortic arch curvatures,
navigability through tortuous and narrow anatomies, precision of deployment, and durability over time. In
adjunct, TEVAR should also avoid any excessive stress on the aortic wall at the landing sites to prevent
retrograde dissection (RTAD) or stent graft-induced new entry tear (SINE).

The precision of deployment is mainly dependent on the mechanism of endograft deployment.

Currently, endografts have two possible mechanisms. The majority of devices present a pin-pull method of
delivering the graft by unsheathing it in a proximal to distal fashion. Thus, deployment is partially