Discussion
Even if the surgery of an acute Debakey type I aortic dissection is
performed with an open distal anastomosis and is mostlikely managed by a
hemiarch aortic reconstruction, this approach has a main disadvantage,
that is to leave entry tears in the proximal descending thoracic aorta
leading to false lumen patency in some patients, increasing the need for
re-operation7-10. Total arch replacement with Frozen
Elephant Trunk allows for distal extension of a stent graft implant into
the true lumen of the descending aorta excluding re-entry tears in the
arch and proximal descending thoracic aorta. In the setting of acute
aortic dissection and deeply ill patients, this approach can increase
the CPB and circulatory arrest times, and exposes patients to additional
risks of paralysis, stroke and haemorrhage11,12. It
may be more useful in particular situations in the setting of aortic
dissection like when there is arch aneurysm, or there is an entry tear
within the arch or in the proximal descending thoracic aorta associated
with the dissection13.
Between these two approaches, the AMDS represents a novel hybrid
solution providing long thoracic coverage alleviating malperfusion and
excluding entry tears without significantly increasing the complexity of
surgery4-6.
DARTS trial has shown a good rate of aortic remodeling. However, this
was a composite criterion; positive remodeling was defined on evidence
of false lumen obliteration, complete false lumen thrombosis and
favourable changes in aortic dimensions14,15. Our
real-life experience shows that these results are more the consequence
of lumen’s diameters correction than a complete false lumen thrombosis,
being possibly due to the primary entry tear exclusion. There was no
need for a redo surgery in our four patients, but we think that the
presence of Nitinol in the arch could jeopardize a second procedure at
this level.
In the two patients having intestinal malperfusion we noticed clinical
improvement. One of them remains having intestinal angina due to
dissection of the superior mesenteric artery. Favourable changes in
aortic true lumen and false lumen dimensions were found in most of our
patients but the AMDS was compressed at the isthmus in one of them. We
did not have any mortality in our patients. This shows that AMDS is a
reliable and secure device. However, its benefits remain unclear when it
comes to a positive remodeling and seems less likelihood comparable to a
frozen elephant trunk. The main reason seems to be an insufficient
radial force of the AMDS, which tend to lengthen rather to expand.
Many studies addressing the radial force of endovascular stents
emphasized on the importance of understanding radial force when
selecting a stent for every patient. Radial force of endovascular stents
provides effective support for blood vessels, maintains adequate lumen
patency, and secures fixation to artery wall16. It
varies among stent designs, and differences depend on the type of
stents, the site of deployment or layer characteristics of each
stent17,18. In vivo, endovascular stents would be
affected by the vessel curvature, blood pressure, vascular smooth
muscles characteristics and much more dynamic
factors17. Surgeons should evaluate the possibility of
stent deformities during and after surgery19. It is
believed that treatment of dissection with endovascular stent requires
fewer radial force compared with the treatment of aneurysm because too
much radial force at distal ends may lead to new entry tears. However,
the arch geometry for thoracic aorta requires larger radial forces to
seal20. In its initial experience on AMDS stent,
Montagner et al. concluded that the low radial force of AMDS stent is
intended just to readapt the intima against the media and adventitia and
it is the subsequent expansion of the true lumen that will drive the
resolution of malperfusion21. Furthermore, they
emphasized on the importance of low radial force of the AMDS stent which
can unlikely damage the intima. They also reported three failures of
device deployment, one of them being due to high turtosity of the aorta
causing kinking and incomplete AMDS expansion22.
Eventhough we observed improvement of malperfusion, this may be
attributed only to primary entry tear resection. Actually, the radial
force of the AMDS is not adequate to guarantee distal expansion of the
true lumen, especially in case of visceral malperfusion and this was
seen in one of our patients. AMDS implantation should be avoided in
patients with aortic calcifications or kinking to prevent incomplete
stent expansion.
Another feature should be mentioned is that the AMDS is an uncovered
stent. In this condition, any entry tear not excluded by this bare stent
will remain active. This is why, we should absolutely avoid AMDS
implantation in patients with any primary entry tear in the
aortic arch.
The main limitations of this study remain in its small sample size, its
retrospective design and the absence of long-term follow-up.