Discussion
Endovascular repair is the treatment of choice for aneurysms or
dissections of the thoracic descending aorta. When the disease extends
to the arch, endovascular treatment is not a good option in most cases7 and open repair is challenging. The development of
hybrid prostheses and the FET procedure8-10 has
simplified the surgical treatment of these pathologies, allowing either
a single-stage open procedure, or facilitating an open or endovascular
second stage11,12. In acute and chronic dissections
FET stabilizes the true lumen, covers the reentry sites in proximal
descending thoracic aorta and promotes false lumen thrombosis and aortic
remodeling, reducing the risk of distal aorta rupture and
reinterventions3-5.
Two different hybrid prosthesis are available in Europe: The E-vita Open
(Jotec GmbH, Hechingen, Germany ) and the Thoraflex
(Vascutek, Terumo, Inchinnan, UK ). The E-vita Open is the
prosthesis of choice at our center. Its main advantage is the
intussuscepted position of the arch prosthesis, which facilitates the
distal anastomosis. On the contrary, the lack of a side branch requires
additional maneuvers to establish early reperfusion.
Authors from Essen have reported the greatest experience with E-vita
Open prosthesis. They operated on 307 patients from 2005 to 2018.
In-hospital mortality was 13.4%. Permanent cerebral and spinal cord
deficit occurred in 7.2% and 2.9%, respectively13.
Freedom from reintervention (open or endovascular) in distal aorta was
73% at 8 years. In acute type A aortic dissections, the false lumen
remained thrombosed or resolved completely along the stent-graft aortic
segment in 90% of patients. Authors from Hannover and Bologna have
published their combined experience in 437 patients from 2007 to 2017.
Three different hybrid prosthesis were used: the Chavan-Haverich
(Hannover, Germany ), the E-vita Open and the
Thoraflex14. In-hospital mortality was 14.9%.
Permanent stroke and spinal cord injury rates were 10.8% and 5.5%,
respectively. 23.1% of patients required an additional procedure, open
or endovascular, during follow-up.
Although our series is still short, results are similar to those centers
with greater experience. In-hospital mortality, permanent stroke and
spinal cord injury were 7.1%, 3.6% and 1.8%, in spite of a high
preoperative risk (type A acute dissections 32.1%, urgent surgery
37.5% and previous cardiac surgery in 19.6%). This is due in part to
an adequate patient selection, a case-to-case procedure planning, a
limited and consistent operating room team (surgeon, nursing,
anesthesiology and perfusion) and the standardization of the procedure.
In our opinion, FET procedure is more reproducible than standard surgery
in complex thoracic aortic disease, enabling small groups like ours to
have comparable outcomes to bigger centers.
Since 2013 surgical technique has evolved. We have moved the distal FET
anastomosis to Zone 0-2, started to perfuse the LSA during lower body
circulatory arrest and perfusion in the thoracoabdominal aorta is
reestablished once distal anastomosis is performed. Tsagakis et
al showed that the combination of Z2 anastomosis, LSA perfusion and
early reperfusion reduced the risk of postoperative renal replacement
therapy, prolonged intubation, re-exploration for bleeding and laryngeal
nerve lesion13. In our series in-hospital mortality
and permanent stroke were reduced to 3.2% and 0% in the last two years
(group II), respectively. This is probably related not only to the
technique improvement but also to the greater experience. Z0, 1 o 2
anastomosis is less technically demanding. In addition, it is easier to
reach in case of bleeding, reduces the risk of laryngeal nerve injury
and avoids left pleural cavity opening.
We switched to bilateral antegrade cerebral perfusion because it is an
easy maneuver which warrants an adequate perfusion of both
hemispheres15. Although a very low stroke rate has
been published with unilateral perfusion16, concern
remains when the duration of selective perfusion is more than 50
minutes17.
Z2 anastomosis is combined with debranching of the LSA with an 8-mm
dacron graft or all three supra-aortic arteries with a trifurcated graft
during cooling. In this way, FET procedure is performed under perfusion
of all supra-aortic arteries, improving cerebral and spinal cord
perfusion during lower body circulatory arrest. To date, we have been
able to dissect the LSA during cooling in all cases. When anatomy is
unfavorable with a displaced LSA origin, an extension of the sternotomy
incision to the left neck is done in order to get a wide left carotid
artery dissection and mobilization. Alternatively, an extra-anatomic
bypass to axillary artery through second intercostal space can be
performed3.
Other improvements in our surgical technique were the interposition of a
graft for arterial cannulation and the use of crystalloid
Bretschneider´s solution for myocardial protection. First, the
innominate artery became our first-choice artery for cannulation, as
additional incisions are not required, and it is easy to access. In
addition, an 8mm dacron graft is now systematically interposed to
diminish the risk of retrograde dissection and improve distal
perfusion18 . Secondly, due to the complexity of this
procedure, optimal myocardial protection plays a key role in achieving a
successful outcome. Crystalloid Bretschneider´s cardioplegia allows a
prolonged myocardial protection in a single dose19.
Finally,
The growing experience and the shorter lower body circulatory arrest
time (Group I 54±20min versus Group II 33±10min, p<0.001) made
it possible to raise nasopharyngeal temperature (Group I 22±3ºC vs Group
II 25±3ºC). Length of stent graft was significantly shorter in Group II
(135.5±5mm versus 150±9mm), which is explained because acute dissections
are more frequent in this group (45.2% versus 16%). In acute aortic
dissections, shorter stent grafts (130mm) are enough to cover the
reentry sites in proximal descending thoracic aorta and promote false
lumen thrombosis.
We must not forget that FET is a major surgery which combines prolonged
time on CPB, hypothermic circulatory arrest and is frequently performed
in high risk patients, so it is not exempted of significant
complications3-5,13,14. Permanent stroke and specially
spinal cord ischemia are the most feared and devastating. In a recent
meta-analysis, Preventza et al analyze the pooled outcome of 3154
patients from thirty-five studies who underwent a FET procedure.
In-hospital mortality was 8.8%, and permanent stroke and spinal cord
injury (SCI) rates were 7.6% and 4.7%, respectively. Stent length of
15cm or greater and coverage extending to T8 were associated with a
higher risk of spinal cord ischemia. The proposed mechanism is the
compromise of collateral flow from segmental arteries. Although its role
is unquestioned, there must be other factors involved, because the
incidence of SCI in endovascular treatment of thoracic aorta has a
significant lower rate21. During open surgery, a
period of spinal cord ischemia occurs during circulatory arrest. During
SACP spinal cord is not perfused below T8-T9 and protection depends
primarily on temperature22.On this basis, spinal cord
is at risk in FET procedures at moderate (28º-32º) temperatures with
long systemic circulatory arrest times (>60min). A third
factor is an inadequate spinal cord perfusion in the postoperative
period. Spinal cord suffers an ischemic insult during circulatory arrest
and several segmental arteries are occluded, so a period of systemic
hypotension can trigger the SCI23. It is critical to
maintain an adequate perfusion pressure during perioperative period,
raising mean blood pressure over 70mmHg. Spinal cord perfusion pressure
can also be improved with the use of intraoperative CSF
drainage24. Other factors involved in neurological
injury are hypoxia, anemia, hyperglycemia and
hyperthermia25.
Paraplegia occurred in one patient: a 67-year-old woman operated in an
emergent situation because an acute type A aortic dissection. A 22x130mm
E-vita Open prosthesis was implanted in zone 0. She was extubated after
six hours without any neurological deficit. 24 hours after surgery she
presented a sudden massive hemorrhage and sustained severe hypotension.
She was transferred to the operating room and bleeding was controlled.
When she was extubated, 48h later, paraplegia was present. Magnetic
resonance imaging showed ischemic damage at T8 level. Despite
hemodynamic and metabolic optimization and CSF drainage, paraplegia was
permanent. Due to her small size (155 cm in height) the stent graft
covered thoracic aorta until T9. Our hypothesis is that although
collateral flow compensated initially the occlusion of segmental
arteries, hemorrhage and subsequent sustained hypotension triggered the
ischemia.
This study has several limitations. First, although data is collected
prospectively, its analysis is retrospective. Second, it is a single
center experience, which makes difficult to support the external
validity of our results. Finally, the sample size is small. We have
almost doubled the number of procedures since we started the FET
program; but, still, the center volume is low as compared to others
(Bologna, Essen or Hannover).