2.4.1 Timing of TEVAR and Aortic Remodelling
Several studies showed that the long-term aortic remodelling is
influenced by the timing of intervention and the different zones of
dissection. This was addressed in a recent review by Jubouri et al.
[4] who summarised the evidence in the literature on timing on TEVAR
in relation with results, and concluded that performing TEVAR during the
subacute phase of un-TBAD yield optimum results, with those being
comparable to the acute phase but superior to the chronic phase. A
comparative study demonstrated a post-TEVAR reduction in the maximum
aortic diameter in the acute and early chronic groups (-4.3 ± 9.3 vs.
-5.2 ± 6.9). In contrast, the late chronic group showed a significant
increase in the maximum thoracic aortic diameter post-TEVAR. (2.5 ± 4.6
mm, P<0.001) [56]. Similarly, Torrent and colleagues
[7] reported a non-significant difference in the degree of
dissection extension between interventions in the acute vs. subacute
stages of TBAD.
The VIRTUE registry showed a significant reduction in FL area in acute
and subacute groups compared to the chronic group [54]. Patients
with acute TBAD showed a more consistent degree of remodelling (thoracic
FL thrombosis in 80% to 90%) than those with a chronic TBAD (38% to
91%) following TEVAR [55]. Yuan and colleagues [5] further
validated these results, concluding that the first three months after
the onset of symptoms of TBAD represented the optimal aortic plasticity
for intervention for remodelling post-TEVAR.
While timing showed no association with FL thrombosis in the proximal
and distal descending thoracic aortic zones (P > 0.3), FL
thrombosis inferior to the diaphragm was significantly lower in patients
with a chronic TBAD(P=0.035) [54].
True lumen expansion results from the stent-graft placed within the TL
of the thoracic aorta covering the primary entry tear. By sealing off
the primary entry tear, it provides scaffolding support and ensures
blood flows distally within the TL. The ADSORB trial [17] showed a
significant increase in TL diameter and reduction in FL diameter within
the first year of follow-up following TEVAR. Yet, the INSTEAD-XL trial
[16] required a five-year follow-up to demonstrate this significant
difference. This difference could be attributed to the timing of patient
enrolment in both trials as the ADSORB trial patients were enrolled
during the acute phase of dissection (<14 days). Those in the
INSTEAD-XL trial were recognized as stable and were enrolled during the
subacute phase. Conversely, results from the VIRTUE registry [54]
showed that the TL expansion was not related to the timing of TEVAR.
Another study by Andacheh et al. [57] showed that the rate at which
the TL expands after TEVAR is not parallel to that at which the FL
shrinks; the expansion of the TL plateaued after 12 months, while the
shrinkage in the FL continued beyond 12 months post-TEVAR. This can
further ascertain the assumption that most of the TL expansion is
attributed to the scaffolding effect of the stent-graft implantation.
Although the FL regression and the TL expansion seem to demonstrate a
significant change following the treatment with TEVAR, this is not the
case with the reduction in the maximum aortic diameter. In fact, some
studies showed a further slight expansion of the maximum aortic diameter
[52, 58]. See table (3)
Although FL thrombosis is considered as a primary predictor of aortic
remodelling, there is evidence not all thrombosed FLs have positive
remodelling outcomes. A study by Kitamura showed post-TEVAR FL
thrombosis was achieved in 74%, whilst only 47% achieved descending
thoracic aortic remodelling. Therefore, descending aorta remodelling was
reported to remain uncertain, especially when associated with an
initially large aortic diameter [59].
Another study by Omura et al. [58], patients with un-TBAD in the
acute-subacute timing exhibited smaller aortic diameter. All the
patients offered TEVAR in this time period showed significant shrinkage
of the proximal aorta. However, distal to the stent-graft, shrinkage was
observed in 50% only. This study has demonstrated the importance of
radiological surveillance post-TEVAR. Up to 17.8% who underwent TEVAR
showed aortic dilation at the distal landing zone [58]. Furthermore,
Xie et al. [8] studied abdominal and thoracic FL as separate
entities in the follow-up and showed greater than 50% have a patent
abdominal aortic FL post-TEVAR in both the acute and subacute phases.
Several other studies established this segment-specific approach for the
long-term evaluation of aortic remodelling and FL thrombosis [8,
44].
The surveillance of the aortic parameters might be as vital as the
primary intervention for the long-term outcomes. Careful assessment of
the aortic diameter and the degree of FL thrombosis over time can be
very informative about the natural history of the underlying dissection
and its sequelae. The risk of developing dSINE must be considered when
evaluating an expanding aortic diameter post-TEVAR. The emerging data
concerning the aortic expansion distal to the stent-graft needs further
investigation and follow-up to better understand the long-term outcomes
following TEVAR.