COMMENT
Before advent of the ET procedure, the earlier techniques (clamping the
descending aorta or aortic arch for Stage II, or performing Stage II
under DHCA through a left thoracotomy) carried a significant risk of
hemorrhage. Hemorrhage could easily occur during dissection of the
enlarged, fragile upper descending aorta, especially after inflammation
from a preceding aortic arch replacement. The back wall of the aorta or
the pulmonary artery could easily be injured in surrounding the upper
descending aorta.[11]. Multiple ET modifications have been suggested
and tried, and reports on the mid and long-term post-operative mortality
are becoming available.
One-step repair of the entire aorta through a clamshell [12],
trans-mediastinal [13], or left posterolateral thoracotomy [14]
have been attempted in order to avoid the need for two separate
operations. However these challenging techniques have achieved only
limited clinical application due to multiple factors, including long
operating time, higher pulmonary complications rates (ranging from 15 to
50%), and near inability to repair segments below the diaphragm
[15].
The staged ET procedure is thought to decrease the pulmonary
complications and negates the need for proximal descending aorta
dissection, hence avoiding injury to adjacent anatomic structures such
as the pulmonary artery, esophagus, and phrenic nerve [4].
Frozen elephant trunk is another technique introduced in 2003 [6]
utilizing a custom-made prosthesis. The proximal portion consists of a
Dacron sleeve for traditional surgical anastomosis; and the distal part
consists of a stent graft [16]. Experience with the frozen elephant
trunk is rapidly accumulating. It can be said, in summary, that the
initial operation is generally well tolerated, but a risk of paraplegia
is incurred, especially with all but the shortest stent portions
[17]. In contrast, paraplegia is quite unlikely with a non-frozen
Stage I elephant trunk (except with very long elephant trunks) . In
support of the frozen elephant trunk option is the issue that the
conventional elephant trunk (used in our experience) can be difficult to
retrieve and utilize as a proximal landing zone for a later endovascular
extension.
Indeed, subjecting patients to two major surgeries carries real risks of
morbidity and mortality. Several retrospective reports have discussed
the mortality rates for each stage. In our cohort, the operative and
30-day mortality rate after Stage I in 152 patients was 3.3%, with
reported rates ranging from 2% to 14% [7, 11, 18, 19]. Our
inter-stage mortality rate in patients awaiting Stage II was 8.3%, with
reports ranging between 2% and 11% [7, 20, 21]. This comes in a
patient population with 31.6 % having undergone a previous cardiac
surgery before Stage I. Fortunately, most of our patients who were
planned for Stage II eventually underwent repair. We had only 1 patient
who was lost to follow up and 5 patients who expired, not from rupture,
advocating for earlier rather than later second stage [7]. It is
notable that in the inter-stage period – beyond the first 30-days –
there were no cases of aortic rupture. Our mortality rate in the second
stage performed in 58 patients was 10.3%, which again is consistent
with previous reports [7, 11, 18]. The continued mortality of 6
patients within the first year after completion of Stage II shows how
serious is the disease of mega-aorta, often with substantial non-aortic
comorbidities.
In our patients, prophylactic placement of an elephant trunk was
performed in 87 patients in whom the descending aorta was mildly
dilated. To date, four patients eventually required repair, and a secure
upper landing zone was already present for replacement of their
descending aorta[21].
Aortic diameter remains a significant predictor of rupture and
dissection in TAA [22, 23] however, it is difficult to predict the
operative mortality and morbidity following repair. The lack of
statistical significance in our variable analysis is understandable due
to low number of events, which is a problem encountered in previous
studies and metanalyses [24]. Our results showed increased composite
adverse events in patients with prior neurologic abnormalities including
prior strokes. Not surprisingly, smoking, coronary artery disease and
prolonged clamp time were also factors associated with increased
complications after Stage I, although this failed to reach statistical
significance.
With advanced techniques of neuronal protection, the risk of spinal cord
injury (SCI) and strokes has decreased. During Stage I, we used straight
DHCA for cerebral protection, which we have shown to be safe and
effective for a duration of 50 minutes or less [15]. We do not
usually use antegrade cerebral perfusion [25]. In our study, the
rate of strokes after Stage I was 4.6%.
Our paraplegia rates were low (3 patients). Routine visualization of the
anterior spinal artery prior to repair may have contributed to these low
paraplegia rates [26]. Utilization of a spinal drain to keep the
lumbar pressure at 5 to 12 mm Hg postoperatively in descending,
thoracoabdominal, and thoracic endovascular aortic repair (TEVAR) has
been shown effective in reducing the risk of spinal cord injury
[27].
An important point to consider has to do with choosing an appropriate
length of the elephant trunk (10-15 cm) to avoid thrombus around the
graft yet permit easy accessibility at Stage II. It is important to
avoid entrapment of the graft in the false lumen in patients with
chronic dissection [20].
Some centers apply a stent graft in the descending aorta prior to
discharge instead of a later Stage II open repair [28]. Although
this hybrid approach has gained popularity, there remain serious
questions about the durability of these stents and the unique associated
complications—especially endoleaks– often mandating later
re-operation.
Enthusiasm regarding ET staged repair may have waned over the years due
to complexity and fear of the inter-stage mortality; however, we feel
that the inter-stage mortality rates and overall outcomes are acceptable
for a disease of this severity. Long-term survival finds our results
durable.