Discussion
Although the diagnostic procedures, surgical techniques, and results are
standardized for patients with isolated ventricular septal defects,
diagnosis is less secure, surgical techniques are more varied, and
published incidence of perioperative mortality, ventricular dysfunction,
and complete heart block are higher in those with multiple defects,
including the Swiss-cheese septum,. Major associated cardiac lesions add
to the complexity of repair.1-72
Analysis of the STS Congenital Heart Surgery Database analysis over a
period of 4 years revealed that, when defects are multiple, it takes
longer to close them. When compared with the more common isolated
perimembranous defects, the rate of heart block is three times higher
with multiple defects. The rate of unplanned reoperation is over four
times higher even with isolated muscular septal defects, and almost
twice as high with multiple septal defects. Before discharge from the
hospital, the mortality rate is over twice as high with muscular septal
defects, and over three times as high with multiple septal
defects.29-32 As already discussed, however, it did
not prove possible to analyse the outcomes in terms of the outcomes for
the anatomical combinations of multiple defects as suggested in our
reviews. This is something that might be achieved in the future, since
the anatomical differences are striking, and certainly impact on the
optimal therapeutic approach.
The key to closure of multiple defects is accurate identification, edge
detection, and proper cavitary entry. Guidance for closure have been
described by multiple investigators using three dimensional color-coded
echocardiography, echocardiographic en-face reconstruction of the right
ventricular septal surface, contrast enhanced and multidetector computed
tomography, fast gradient magnetic resonance cardiac imaging,
angiocardiography, and perventricular wire placement, or by
cardioscopy.1-9,14,22-28,71
Taken together, these investigations collectively provide comprehensive
assessment of anatomical information to obtain an accurate preoperative
diagnosis, yet it remains difficult to ascertain whether all defects are
recognised, particularly when one large defect is
non-restrictive.1-28,59,64,71 Our review revealed
several instances of diagnosis of additional defects intraoperatively,
postoperatively, or at necropsy.1,7,13
The optimal surgical repair involves complete closure of the multiple
defects. Ideally the moderator band and septomarginal trabeculation
should remain intact, without a need for ventriculotomy, without
compromising the size of the ventricular cavities, without producing
ventricular dysfunction, surgical complete heart block, aortic and
tricuspid regurgitation, and without compromising the coronary arterial
flow. That this ideal has yet to be achieved is evident from the
numerous surgical and interventional techniques described, along with
short-term follow-up studies that report an undesirable incidence of
perioperative mortality and morbidity.1-72 Residual
defects, and postoperative myocardial dysfunction, are still the
Achille’s heel of poor surgical results. They are related mainly to the
uncertainty of location of the defects, and the difficulty in obtaining
complete closure without right and/or left
ventriculotomy.1-17,19-27,29-32,41,43,46-53,59,61,65
With the evolving knowledge of the complex variable anatomy,
individualized surgical techniques have been described to suit the
different anatomical variants. Some approaches, furthermore, are
suitable for several variants. All surgeons acknowledge, nonetheless,
that these defects, when multiple, are difficult to close, particularly
in small infants presenting with congestive cardiac
failure.1-17,19-27,29-32,41,43,46-53,59,61,65
It may be hard to recognize the boundaries of defects because the
moderator band and multiple trabeculations hide apical defects, while
Swiss-cheese defects may remain misdiagnosed.1-72Visualization and closure of most muscular defects is usually possible
via a right atriotomy. Exposure of apical defects from the right side,
however, has been plagued by poor visualization, and the uncertainties
of identifying the true margins of the defects when approaching through
the coarse trabeculations of right ventricular
apex.1-72 These problems are then still further
exacerbated in the setting of the Swiss-cheese septum. It is because of
the limited exposure, and difficulties in exploring Swiss-cheese
defects, that banding of the pulmonary trunk is still being performed in
premature infants with low body weight to protect the pulmonary vascular
bed and to relieve symptoms of congestive heart failure to delay
definitive repair.14-17,30-32
As we have discussed, such banding can also have its place in treatment
of individuals with other combinations of multiple defects. Presently,
banding as an initial palliative procedure is being performed in select
institutions under specific circumstances. These include the proximity
of margins of the defect to the atrioventricular conduction axis, which
predisposes to atrioventricular block in small infants when constraints
exist in terms of space for placing a permanent pacemaker. Other
indications include multiple apical defects, particularly the
Swiss-cheese septum, selected patients with large trabeculations
traversing the defects that could interfere with complete closure,
co-existing perimembranous and muscular inlet defects, an associations
with coarctation in infants aged less than 2 months, association with
lesions such as twisted atrioventricular connections and those selected
individuals deemed generally to be at
high-risk.13,14,16,17,30-32,37 The staged approach,
furthermore, is known to promote spontaneous closure of some of the
smaller defects. Against these potential advantages must be weighed the
deleterious effects of biventricular muscular and fibrous hypertrophy
and long-lasting hypoxia leading to arrhythmic events, increased
mortality, and chronic heart
failure.22-24,30,32,41,42,48
Since the pulmonary vascular bed is both pressure and volume overloaded,
there is difficulty in determining the optimal tightness of the band.
Hence the need for frequent reoperations for adjustment. The added
complexity of the second stage includes pericardial adhesions, need for
pulmonary arterioplasty, damage to the potential neoaortic valve and
right ventricular hypertrophy, further contributing to difficult
exposure of septal defects.16,17,29-32 To address
these concerns, Corno and associates introduced the telemetrically
adjustable FloWatch pulmonary artery band (FloWatch-PAB®). Use of this
approach not only eliminates the requirement of reoperation to adjust
the band, but also allows for precise and progressive tightening over
days or weeks.16,17 The non-circular shape of
FloWatch, furthermore, maintains the pliability of pulmonary arterial
wall and avoids pulmonary arterioplasty.
The approach through the left ventricle still retains its advocates.
Thus, when using this technique, Aaron and Hanna demonstrated that
exposure and repair of apical defects was much
easier.11 It is particularly appropriate for those
cases with a solitary defect seemingly having multiple channels when
assessed from the right ventricle. Its use has been advocated by
multiple surgeons producing small series with excellent short- and
long-term results. Recently, a limited apical left ventriculotomy
approach has been introduced.2,57,61,65 Debate
continues, nonetheless, with regard to its potential risks. The exposure
gained can also be disappointing at times. Because of all these
considerations, some argue that the risks, in the long-term, are
unacceptable, since they include apical dyskinesia, aneurysm formation,
left ventricular dysfunction, ventricular arrhythmia, and the need for
cardiac transplantation.2,30-32,57-61,65,66 The
mechanisms identified that result in left ventricular dysfunction and
aneurysm formation have included damage to epicardial coronary arteries,
the myocardium, and the left ventricular conduction
system.11,58,60,61 It is also the case that the
precise anatomic location and orientation of the ventriculotomy has
great impact on the results. Waldhausen and DiBernardo, for example,
demonstrated that a longitudinal left ventriculotomy causes less
disruption to coronary vasculature, less injury to papillary muscles,
better preservation of ventricular function, and smaller areas of
ischemia when compared to transverse lesions.2,58
The advocates of an apical right ventriculotomy have demonstrated the
safety and effectiveness of this approach for large solitary apical
defects with multiple overlying trabeculations, and for apical and
anterior defects.12-15 The technical features include
a limited right ventricular incision that is close to left anterior
interventricular coronary artery without endangering the vessel. As
described by Tsang and associates, a ventriculotomy in this area allows
entry to the space between the papillary muscles and the
septum.15
All surgeons acknowledge that the Swiss-cheese septum is particularly
difficult to close, particularly when encountered in neonates and
premature infants with low body weight presenting with congestive
cardiac failure.1-72 The true Swiss-cheese septum
emdodies all the morphologic features of so-called “non-compaction”.
Repair of the non-compacted septum essentially involves ventricular
septation, either with an oversized patch, or by right ventricular
apical exclusion. Outcomes of such procedures may be complicated by
abnormal ventricular function requiring cardiac transplantation. In many
circumstances, initial placement of an adjustable pulmonary arterial
band remains a safer and desirable
option.14,16,17,30-32 The techniques of “over-sized
pericardial patch”, “composite patch”, “double patch sandwiching the
septum”, “felt sandwich patch” have all been described, with or
without transection of moderator band/septal trabeculations without left
ventriculotomy.1-8,79 The majority of patients
required prolonged diuretics, angiotensin converting enzyme inhibitors,
thereby suggesting impairment of left ventricular function in the
postoperative period. The non-compacted septum can be notoriously
difficult to identify before the initial repair. Once obvious defects
have been closed, additional defects can be unmasked, and may require
additional intervention.1-8 If a large patch is used
to cover the entire septum, it is desirable to address multiple points
of fixation to avoid the development of aneurysmal new
septum.4,5 Although the use of oversized pericardial
patches yielded good results, residual defects are frequently reported,
along with reduced right ventricular size, and late complications
including cardiac cirrhosis, late opening of the oval fossa, and atrial
tachyarrhythmias.68
It follows that there are wide variations in practice between centers in
the approach to interventions for multiple muscular septal defects. Many
surgeons prefer to repair mid muscular septal defects in the operating
room using traditional techniques.7-14,38,72 Recently,
transcatheter device closure and hybrid techniques for closure of
multiple muscular septal defects have reported encouraging early
outcomes. Percutaneous device closure in infants below 5 kg poses a
variety of challenges because of low body weight and poor venous
access.22-25,28,52-55 The stiff delivery catheters and
sheath can splint open the tricuspid valve, mitral valve, and/or aortic
valve, leading to arrhythmias, heart block and hemodynamic
decompensation. In these clinical situations, a perventricular hybrid
approach is a feasible “off pump” therapeutic option with acceptable
mortality and morbidity.23-25,51-55,69
Recommendations were suggested in 2011 by the American Heart Association
for device closure of multiple muscular septal defects. Infants weighing
more than 5 kg, and children and adolescents with hemodynamically
significant shunts were placed in Class IIA. In Class IIB were placed
neonates, and infants weighing less than 5 kg with hemodynamically
significant lesions and associated cardiac defects requiring
cardiopulmonary bypass, albeit for initial hybrid perventricular closure
off bypass, followed by surgical repair of the remaining defects.
Neonates, infants and children with hemodynamically significant inlet
multiple septal defects with inadequate space between the defect and the
atrioventricular or arterial valves were not recommended for
closure.28 When considering these recommendations, it
is those multiple defects located in the mid, apical, inferior, or
anterior parts of the apical septum that are most amenable to closure in
transcatheter fashion.19-28,52-55 In recent years,
with the introduction of the Amplatzer muscular and perimembranous
occluders, the hybrid perventricular technique has been used for
selected individuals with perimembranous and outlet defects to avoid
surgical intervention, or to simplify operative
repair.67,73-78 In the multicentric trial on device
closure carried out in the United States of America, almost
three-quarters of individuals had only a single device inserted. In
nearly one-fifth, however, it was necessary to use two devices, while
three devices were needed in just over
one-twentieth.28 Other investigators have also
reported successful closure with multiple
devices.28,52-55 The exclusion criteria of device
closure include weight less than 3 kg, distances of less than 4 mm
between the defects and valvar leaflets, pulmonary vascular resistance
greater than 7 indexed Wood units, sepsis, more than trivial aortic or
tricuspid regurgitation, obvious aortic valve prolapse, diameters
greater than 10mm, preoperative arrhythmias, and contraindications to
antiplatelet agents.19-28 Patients with multiple
ventricular septal defects with associated defects or undergoing hybrid
procedures, represent a set of very particular clinical situations. A
collaborative approach using transcatheter/hybrid device closure
followed by surgical repair is emerging when preoperative evaluation is
suggestive of relatively inaccessible location of the septal defect
which may necessitate an incision in the systemic ventricle and those
with complex associated lesions.28-32,45,61,78 The
advantages of percutaneous closure include avoidance of transection of
trabeculations, avoidance of ventricular incisions and immediate
confirmation of adequate closure. As already discussed, however,
multiple adverse events have been reported in four series of
intraoperative closure.28,60,67-70
Pooling the available data for interventional closure of multiple
defects reveals an incidence of such adverse events of between 2.8% and
45%. The reported complications are many and varied. They include
arrhythmias, cardiac arrest, device embolization, residual shunting,
cardiac perforation, and even procedure-related
death.19-28,60,66-70 When compared with surgery, in
which complete heart block appears early postoperatively, complete heart
block is unpredictable after device closure, and is a late problem.
Direct compression, inflammatory reaction, and formation of scarring in
the conduction tissues have all been variously incriminated as the
causative mechanism of complete heart
block.19-28,66-70,73,80