Discussion
Accurate reimplantation of the coronary arteries is the key component in
the success of the arterial switch procedure. This must be achieved
without creating undue tension, torsion, or kinking of the stems of the
coronary arteries or their proximal branches. During the evolution of
the procedure, certain patterns have been identified as problematic. Of
particular concern are the so-called intramural variants, and the
arrangements when all arteries arise from a single sinus. During the
evolution of the operative procedure, so-called “looping” was
considered a potential problem, as was juxta-commissural origin of the
arterial orifices. Presence of associated defects also created
additional problems, as did side-by-side arterial trunks in the
so-called Taussig-Bing variant.4,12,31,47 With ongoing
experience, many of these potential problems have been mitigated. It is
now generally considered that translocation is feasible for all variable
patterns, although origin from the nonadjacent sinus may now be
considered a contra-indication.29
In the initial technique as described by Jatene, the coronary arteries
were not transferred to the new aorta until after anastomosis of the
aorta to the initial pulmonary root.31 Translocation
to a distended root was then recognised as helpful in avoiding the need
for prolonged myocardial ischemia, preventing recurrent reperfusion
injuries, and permitting visualization of the newly implanted buttons
and suture lines prior to reconstructing the new pulmonary
trunk.21,22,31,47,E1-E4 The approach, however, posed
the risk of damaging the neoaortic valvar leaflets when creating the
required openings in the neoaortic root. Placement of a marking stitch
at the facing neoaortic commissure was proposed to mitigate this
difficulty.E5 The essence of the technique is to punch
appropriately sized holes, and then to anastomose the mobilized buttons
to these openings.13 A key point is to bring the
initial pulmonary root towards the buttons, rather than stretching the
buttons towards the new root.E6 Good midterm results
were reported using this strategy.59
Despite the success of the initial technique,31advantages came to be recognised of the trapdoor
technique.33,39 In this modification, the arterial
buttons are translocated to the neoaortic root prior to reconstruction
of the neoaorta. This approach was considered of particular value in the
setting of retropulmonary looping of the circumflex artery, which is the
second commonest pattern, or the main stem of the left coronary artery.
These variations create a shorter distance, and an acute turn, between
the coronary artery and its new sinus, with potential kinking or
distortion during translocation. Similar advantages were suggested for
the trapdoor approach in the setting of anterior
looping,12 which has the potential risk of stretching
or bowstringing during translocation .4,13,E4 Further
advantages were suggested if the arterial buttons were placed at or
above the neoaortic anastomosis.33,35 Since reports of
its success were published by the group working at Marie Lannelongue
during the mid-1990s, the technique has gained significant
popularity.12,52,54,E6 Some suggested changes,
however, were not without their own problems. In the modification
proposed by Vouhe, for example, with each button playing the role of the
trapdoor flap for the other button, arterial obstruction within one year
occurred in over one-quarter of patients. These findings understandably
led to the abandonment of the modification.34 Another
modification was to create trapdoor flaps in both arterial
roots.44 Good short-term results then accrued for five
consecutive individuals found to have looping in the setting of single
sinus origin.44 Yet another successful modification
was to augment the relocated coronary artery using a patch of autologous
or treated pericardium or pulmonary artery.4,46 All of
these modifications are designed to avoid kinking or stretching
subsequent to transfer. It follows that identification of the optimal
location for each anastomosis remains crucial. As yet, however,
long-term results of these individual techniques are not available so as
to determine which might be preferable.4,34,36,44,46
Problems were encountered initially when looping patterns were found in
the setting of origin of coronary arteries from each of the adjacent
sinuses. The techniques as described above have resolved most of the
difficulties. Problems still remain when all arteries arise from the
same aortic sinus,6 a finding in up to one-sixth of
individuals in some series.40-43 The difficulties
relate to the limited mobility when a short main stem feeds the looping
artery or arteries. Comparable limited mobility is found should the
arteries arise from the same sinus through double or triple
orfices.2,4,5,8,10,12,19,27,28,52 Specific techniques
have also been proposed to mitigate these problems. Thus, when arising
from a solitary main stem, a button can be detached and inverted using
the technique proposed by Yacoub,4 or else anastomosed
to the neoaortic root using the trapdoor
technique.33,39 When there are multiple orifices
within the sinus, then as is the case for juxtacommissural origin from
both adjacent sinuses, creation of an aortopulmonary window is a good
option.40-43 The group working at Marie Lannelongue,
however, had initially modified the technique of Yacoub as suggested
above, only to abandon it because of kinking. Instead, they promoted the
dual button trapdoor transfer as described by Asou and
Mee.11,12,17,33,39 An additional high risk of direct
implantation had been identified in specific situations when the angle
between a line drawn between the centres of the arterial roots and that
drawn from the neoaorta to the coronary arterial orifice exceeds 75
degree.20 In this setting, augmentation using a
pericardial hood was shown to maintain a natural lie of the transferred
coronary artery, and to produce a good long-term
result.46 Others had suggested using a short
autologous pericardial tube,E3 but this risks the
formation of thrombus, as well as extrinsic compression by the newly
constructed pulmonary pathways. Problems also occurred subsequent to
augmentation using a pulmonary arterial flap, with the coronary artery
being abnormally positioned even after successful
translocation.21,44,E2,E3
It is the intramural arrangement, nonetheless, that still poses the
greatest risk to the patient. If undetected prior to the procedure, the
artery may inadvertently be transected during the initial aortotomy. The
aortotomy should be performed in a safe area, revealing the location of
all the arterial orifices before the aorta is
transected.E7,E8 If the intramural artery is
para-commissural, or inseparable from the other arterial orifice arising
from the same sinus, the commissure itself should be detached,
permitting harvesting of the button as a single disc. If the intramural
component is stenotic, it must be completely unroofed prior to
resuspending and reconstructing the neopulmonary
valve.11,17,39,46,47,E7-E9
Once recognised, two methods have evolved to mitigate the problems of
the intramural arrangement. The first is to separate the orifice of the
intramural artery from its sinus, either as a confluent button
containing the other artery, or as separate buttons. The second method
is to leave both arteries within the sinus, and to create an
aortopulmonary window roofed by a patch or autologous tissue. Each
technique has advantages and
disadvantages.11,17,39,46,47,E7-E9 If two buttons are
to be successfully created, there should be more than 2 millimeters
between the orifices. Each button can then be handled using the trapdoor
approach.33,39 This technique, however, is technically
demanding. An insufficient cuff of sinusal wall has been found to lead
to more angled rotation of one or both
buttons.11,17,33,39,48 Transfer of a confluent button
can be achieved using a medially based trapdoor supplemented by
pericardial or pulmonary hood augmentation, with this approach avoiding
turbulent flow within the neopulmonary system.47Creation of an aortopulmonary window, in contrast, by maintaining the
native geometry, is claimed to reduce the possibility of tension,
torsion, kinking or overstretching.37,38,40-44 Use of
a hinged aortic sinus pouch and flap in the latter approach is also
claimed, irrespective of the location of the arteries, to reduce the
risks of thrombosis, shrinkage, distortion, late obstruction,
compression, and neopulmonary arterial
stenosis.37,38,40-44
The commonest reason for early mortality following anatomical correction
has proved to be postoperative ventricular
dysfunction.19,48,49,60 Reports on etiology, however,
are limited and conflicting.E8-E10 Studies conducted
to date have been hindered by the small number of included patients, and
hence their limited statistical power ranging between 20% to
35%.25,26,53,54 We were able to identify nine
retrospective, one prospective, and one meta-analysis specifically
addressing the relationship between coronary arterial patterns and short
and long-term
outcomes.12,13,25,26,30,34,36,57-59,E11-E13 Reported
events have varied from 2% to 11%, with a high early and low late
incidence. Most have been related to kinking, torsion, or
stretching.12,13,25,26,30,34,36,57-59,E11-E13 As with
the operative problems, the events are associated with the intramural
arrangement, retropulmonary looping, and single sinus origin with
multiple orifices. Residual stenosis due to intimal proliferation is
commonly reported.47,51-54,57,E14,E15 Complications
occurring with favourable arterial patterns have been less well
explained. One meta-analysis,26 for
example,26 found looping in the setting of a single
sinus origin to be associated with a 3 fold increase in mortality,
whereas looping when each adjacent sinus supported a coronary artery was
not associated with increased risk. The underlying problem is again
considered to be kinking or stretching of the looping coronary
arteries.26,53,E13-E15 In up to one-tenth of cases,
evidence has been found of extensive lengths of stenosis, or even
occlusion, explaining well some catastrophic clinical
consequences.12,33,39 A small number of individuals
suffer late events, either death or myocardial infarction, following
anatomical correction,54,56,59,E4,E12 with myocardial
revascularization reported at periods of between three months and three
years after the switch.53,54,E15,E16 The causes were
again mostly related to stretching of the translocated coronary arteries
with ongoing somatic growth, and progressive fibrocellular-intimal
hyperplasia..E12,E14,E15 Studies assessing the
capacity of non-invasive methods to predict such obstruction have thus
far been inconclusive.E12-E20 With the increased
resolution of three-dimensional clinical techniques, nonetheless, it is
becoming much easier specifically to identify the postoperative coronary
arterial anatomy, thus offering hope that the reasons for complications
will soon become obvious.E21-E23 Already, when using
coronary angiography, the group working at Marie Lannelongue had
identified postoperative lesions in two-thirds of their patients at a
median of 7 years of follow-up.53 Another angiographic
study, however, identified problems in less than one-twentieth of their
patients after a median follow-up of just over one
year.E12 Others have demonstrated long term problems
in between one-twelth and one fifth of patients, mostly in the setting
of single sinus origin, with the findings considered an important cause
of late death.E13-E15 The optimal management of the
lesions, once identified, remains to be determined. Percutaneous
coronary angioplasty, or surgical revascularization, have thus far been
performed with satisfactory mid-term
results.51-53,E13,E15,E17-E19,E24,E25