BACKGROUND
Structural pathologies of the aortic arch and descending thoracic aorta
(DTA) are notoriously challenging to manage via surgical intervention
and are renowned for being associated with high mortality and
postoperative disability rates, as well as high cost.1Historically, pathologies such as aortic aneurysm and De Bakey Types I
and II (Stanford Type A) aortic dissection warranted multiple
interventions and admissions, and were associated with relatively poor
clinical outcome.2 In an effort to simplify surgical
repair of the aortic arch, the two-stage conventional Elephant Trunk
(cET) procedure was introduced in 1983 by Borst et al . It
involved an initial total arch replacement (TAR) via median sternotomy,
followed by implantation of an elephant trunk graft in a second
procedure (Figure 2).3 Borst and colleague’s technique
enjoyed widespread use until the introduction of the Frozen Elephant
Trunk (FET) approach to aortic repair by Haverich et al. in 2003,
which replaced the free-floating elephant trunk prosthesis introduced by
Borst et al. with a secured stent inserted into the descending
thoracic aorta.4 The FET was heralded for reducing
procedure duration, and rates of postoperative complications associated
with cET, indeed over 28,000 FET procedures were carried out between its
advent and 2014.5 TAR with FET is currently indicated
for repairing aneurysms of the aortic arch and DTA, as well as acute,
chronic, and residual Type A aortic dissection.5
When faced with a Type A aortic dissection, the aortic surgeon is
presented with the option to proceed either a conservative or aggressive
therapeutic approach.6, 7 Whereas the former advocates
the use of an initial hemiarch repair (HAR) before taking further steps
to address the sequalae of Type A aortic dissection, the latter
recommends a TAR with deployment of an FET to control intimal tears and
stimulate false lumen (FL) remodelling.8 The debate
between conservative and aggressive intervention is ongoing – Bashiret al. note that this is in part due to the lack of prospective
studies comparing the two.8 Studies by Rice et
al. and Sun et al. have produced results that seem to suggest
there is no significant difference in perioperative mortality between
HAR and TAR procedures for Type A aortic dissection, and Bashir et
al. highlight that more premptive, aggressive approaches could be
associated with higher rates of 5-year freedom from death, rupture, and
reintervention.8-10 It should also be noted that TAR
not only reduces the risk of further aortic dilation, but is also able
to fully obliterate the distal FL.10
Apart from total versus hemiarch replacement, the surgeon must also
consider the primary differences between cET and FET prostheses deployed
for arch repair. Whereas cET arch repair introduced a free-floating
aortic graft into the DTA true lumen (TL), anastomosed to the distal end
of an aortic arch graft, the FET procedure uses endovascular stent
secured to the native aortic intima and anastomosed to a Dacron arch
prosthesis.3
Although use of the FET is advantageous over cET as it involves only one
surgery and is associated with fewer complications and a lower
re-intervention rate, it remains a technically demanding
intervention.5 The complications associated with FET
are especially debilitating – spinal cord injury, cerebral injury,
and kidney failure are cited as occurring in up to 11%, 26%, and 22%
of cases respectively.11, 12
Notably, the aortic zone at which the elephant trunk stent is
anastomosed to the aortic arch graft is a key issue of
debate.1 When Haverich and colleagues introduced the
FET procedure, distal anastomosis at Zone 3 (Z-3-FET) seemed to be the
conventional approach. However, in recent decades, this technique has
given way to distal anastomosis at Zone 2 (Z-2-FET) - which is now the
preferred surgical approach as it is associated with even better
clinical outcomes than Z-3-FET.5 Following this
paradigm shift, surgeons have began questioning whether proximalising
FET implantation to Zone 0 (Z-0-FET) would further improve surgical
operability and clinical outcomes.1 This begs the
question: is proximalisation of aortic repair from Zone 2 to Zone 0
simply a concept, or true challenge?
Therefore, this review seeks to evaluate current literature and compare
Z-2-FET and Z-0-FET in terms of surgical technique, clinical efficacy,
and incidence of key complications (mortality, neurological injury,
renal injury, recurrent laryngeal nerve injury, and need for
reintervention).