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Key Questions in CONGENITAL CARDIAC SURGERY
A
Aortopulmonary continuity Septal defect
Septomarginal trabeculation
Septal defect
Septomarginal trabeculation
30
Ventriculo-infundibular fold
Supraventricular crest
B
Tricuspid-mitral continuity
Figure 22. Ventricular septal defects defined by the ‘crista’, rather than
location: A) in the so-called ‘supracristal defect’, the myocardial structure
identified as the ‘crista’ is produced by fusion of the ventriculo-infundibular
fold with the caudal
red borders). The phenotypic feature of this defect is the fibrous continuity
between the leaflets of the aortic and pulmonary valves in the roof of the
defect; B) in the so-called ‘infracristal defect’, the structure identified as the
‘crista’ is the supraventricular crest.
limb of the septomarginal trabeculation (white star with
1 Congenital cardiac anatomy
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Septal defect
A
Tricuspid-mitral continuity
Hypoplastic non-muscularised
B
outflow cushions
Muscularised outflow cushions
Septomarginal trabeculation
Pulmonary
root
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Aortic root
Inner heart curvature
Septal defect
Septomarginal trabeculation
Figure 23. A) The defect described by some as being ‘infracristal’ lies
inferior to the structure derived by muscularisation of the proximal outflow
cushions. B) In the defect described by some as being ‘supracristal’, the
proximal outflow cushions have failed to muscularise. The difference
between the two defects, therefore, reflects the varying maturation of the
proximal outflow cushions, rather than the way the defects open relative to
the ventricular septum.
Key Questions in CONGENITAL CARDIAC SURGERY
This explains the phenotypic feature of the supracristal defect, which
•
is better described as being doubly committed and juxta-arterial. The
distinguishing feature is the fibrous continuity between the leaflets of
the aortic and pulmonary valves.
14 What are the phenotypic features of tetralogy of Fallot?
Tetralogy of Fallot is a combination of four morphological features,
•
namely an interventricular communication, biventricular connection of
the aortic root, subpulmonary stenosis and right ventricular
hypertrophy.
There is a wide range of combinations of these morphological
•
features, resulting in no two cases being morphologically identical.
For some time, it was thought that anterocephalad malalignment of
•
the muscular outlet septum or its fibrous remnant, was the unifying
feature of the tetralogy spectrum.
Such a feature, however, is to be found not only in the setting of
•
32
tetralogy of Fallot but also in an Eisenmenger ventricular septal
defect, which is a perimembranous outlet defect associated with
overriding of the pulmonary trunk.
The additional finding required to produce the phenotypical feature of
•
tetralogy is the anomalous formation of the septoparietal
trabeculations. In the tetralogy spectrum, the trabeculations are
usually hypertrophied.
It is the combination of these two features that produces the
•
characteristic narrowing at the mouth of the subpulmonary
infundibulum (Figure 24).
Hearts with this phenotypical feature can show morphological
•
variability in terms of the:
a) type of interventricular communication which can:
i) be perimembranous;
ii) have a muscular posteroinferior rim;
iii) be doubly committed and juxta-arterial;
b) extent of override of the aortic root;
c) degree of obstruction of the subpulmonary outflow tract;
d) right ventricular hypertrophy — which is recognised to be a
haemodynamic consequence of the subpulmonary narrowing.
A
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Malaligned outlet septum
1 Congenital cardiac anatomy
Pulmonary
root
Aortic root
Unobstructed
outflow tract
B
Malaligned outlet septum
Aortic root
Subpulmonary
obstruction
Septoparietal
trabeculations
Pulmonary
root
Septoparietal
trabeculations
Figure 24. Images demonstrating malalignment of the muscular outlet
septum, which in isolation, does not produce the phenotypical feature of
tetralogy of Fallot: A) Eisenmenger defect where the subpulmonary outflow
tract is unobstructed despite the presence of malalignment of the outlet
septum, along with well-formed
Fallot, characterised by the phenotypical narrowing between the
malaligned muscular outlet septum and the septoparietal trabeculations.
septoparietal trabeculations; B) tetralogy of
33
Key Questions in CONGENITAL CARDIAC SURGERY
15 What are the phenotypical characteristics of defects
associated with systemic-to-pulmonary collateral
arteries?
In the setting of pulmonary atresia, the pulmonary arterial supply is
•
derived most frequently either through a persistently patent arterial
duct or via systemic-to-pulmonary collateral arteries (Figure 25).
Systemic-to-pulmonary is a better descriptor of the collateral arteries
•
than major aortopulmonary collateral arteries (MAPCAs), since the
collateral arteries can arise not only from the aorta but also from the
coronary or brachiocephalic arteries.
These two sources hardly ever supply the same lung. Indeed, it is a
•
good working rule that, if systemic-to-pulmonary collateral arteries
are found supplying one or both lungs, the arterial duct will be
absent, unless it provides the sole supply to one lung through a
discontinuous intrapericardial pulmonary artery.
The pulmonary arterial supply via the persistently patent arterial duct
•
is almost without exception found in pulmonary atresia with intact
ventricular septum.
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Pulmonary supply via an arterial duct can also be found in cases of
•
pulmonary atresia with ventricular septal defect, as in the context of:
a) transposition of the great arteries;
b) congenitally corrected transposition of the great arteries;
c) isomerism with a VSD.
Instead, the supply of blood to the lungs through systemic-to-
•
pulmonary arteries is found with frequency only with pulmonary
atresia in the context of tetralogy of Fallot. It is a subset of the hearts
that collectively can be described as pulmonary atresia with
ventricular septal defect.
The pulmonary arterial supply in tetralogy with pulmonary atresia can
•
also be through a persistently patent arterial duct. If via a duct,
however, there will be a unifocal supply to all the bronchopulmonary
segments.
Pulmonary arterial supply through systemic-to-pulmonary collateral
•
arteries is multifocal, since hardly ever does a solitary collateral artery
supply all the bronchopulmonary segments. Instead, the supply is
either direct, or else through anastomoses with intrapericardial
pulmonary arteries.
In rare circumstances, the pulmonary arterial supply in tetralogy with
•
pulmonary atresia can be through an aortopulmonary window, or via
coronary arterial fistulous communications. Discontinuous pulmonary
arteries can be fed through bilateral arterial ducts, or through a duct
Confluent intrapericardial
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A
pulmonary arteries
1 Congenital cardiac anatomy
B
Confluent intrapericardial
pulmonary arteries
Systemic-to-pulmonary
collateral arteries
Aorta
Aorta
Arterial duct
Figure 25. Images demonstrating systemic-to-pulmonary collateral
arteries in the setting of pulmonary atresia, with a supply through: A) a
persistently patent arterial duct to confluent intrapericardial pulmonary
arteries (where the intrapericardial pulmonary arteries supply all of the
bronchopulmonary segments in a unifocal fashion); and B) systemic-topulmonary collateral arteries arising from the descending intrathoracic
aorta, with coexisting confluent intrapericardial pulmonary arteries, which
anastomose with the collateral arteries. In these instances, the
intrapericardial arteries have a limited multifocal supply to some, but not all,
of the bronchopulmonary segments.
35
Key Questions in CONGENITAL CARDIAC SURGERY
in one lung and systemic-to-pulmonary collateral arteries in the other
lung. In the past, arterial ducts with an unusual origin were described
as ‘arteries of the 5th pharyngeal arch’. It is now known that the socalled ‘5th arch’ does not exist.
It remains to be proven as to whether the systemic-to-pulmonary
•
arteries are hypertrophied bronchial arteries.
It is a mistake to seek to distinguish the intrapericardial pulmonary
•
arteries as being ‘native’, as the systemic-to-pulmonary collateral
arteries are equally ‘native’.
16 What is double-outlet right ventricle?
Double-outlet right ventricle (DORV) is the situation in which the
•
larger part of both arterial roots are supported by the morphologically
right ventricle.
The definition of the arrangement existing when both arterial trunks
•
arise from the morphological right ventricle has long been
contentious.
The resolution of these discussions has been provided by the
•
36
concept of the ‘morphological method’, which stated that one
variable feature in the heart should not be defined on the basis of
another feature that is itself variable.
As a result, only the proportion of the overriding arterial trunk
•
supported by the right, as opposed to the left ventricle, is the
determinant of the precise ventriculo-arterial connection, and DORV
is no more than one of the possible ventriculo-arterial connections in
the setting of overriding of either the aortic or the pulmonary root, or
in some instances both arterial roots.
In this setting, the channel overridden by the arterial root will have
•
right and left ventricular borders. Whether the root is supported
predominantly by the right ventricle, and hence in the setting of
double outlet, can be determined by whether the surgeon considers
that they are able to close the right ventricular border.
If this is the case, the ventriculo-arterial connections will have been
•
either concordant or discordant and the surgeon will have closed the
‘ventricular septal defect’.
If the surgeon considers that they have had to tunnel the right
•
ventricular border of the overriding root to the crest of the muscular
ventricular septum, then the ventriculo-arterial connection will initially
have been that of double-outlet right ventricle. The leftward border of
the defect will then have been an interventricular communication,
rather than a ‘ventricular septal defect’ (Figure 26).
1 Congenital cardiac anatomy
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ABC
Figure 26. Relative position of the plane of an interventricular
communication (red dotted line) and the patch (in yellow) used to close
it, where: A) the aorta is committed to the left ventricle in a simple
ventricular septal defect and the patch coincides with the plane of the
interventricular communication; B) there is 50% aortic override in
tetralogy of Fallot and the plane of the interventricular communication is
to the left of the plane of the patch. The patch includes a small portion or
the right ventricular cavity to redirect the flow from the left ventricle to the
aorta; and C) the aorta is committed to the right ventricle and the plane
of the interventricular communication and that of the patch are on the
opposite sides of the aortic root, as in double-outlet right ventricle. A
large portion of the right ventricular cavity is required to redirect the flow
from the left ventricle to the aorta.
37
17 What is a functionally univentricular heart?
A functionally univentricular heart is characterised by an incomplete
•
ventricle, which is of insufficient size to support independently either
the pulmonary or the systemic circulation, such as with a:
a) dominant left ventricle and an incomplete right ventricle;
b) dominant right ventricle and an incomplete left ventricle.
Very few congenitally malformed hearts are found with a solitary
•
chamber within the ventricular mass. If found, such solitary ventricles
are of indeterminate ventricular morphology, although occasionally
Key Questions in CONGENITAL CARDIAC SURGERY
hearts can be found with a dominant right ventricle when the
accompanying left ventricle is so small as to escape clinical
detection.
The majority of hearts that, in the past, were described as ‘single
•
ventricles’ have a dominant left ventricle, with incomplete formation
of the right ventricle due to absence of its inlet component. This is
found either when both atrioventricular junctions are connected to
the dominant left ventricle (double-inlet left ventricle, [DILV]), or when
there is an absence of either the right-sided or the left-sided
atrioventricular connection. The latter arrangement is seen most
frequently in the setting of tricuspid atresia.
These hearts with a double-inlet ventricle, or with absence of either
•
the right-sided or the left-sided atrioventricular connections, together
make up the group of hearts with univentricular atrioventricular
connections.
Hearts with biventricular atrioventricular connections can also
•
produce a functionally univentricular arrangement. This occurs when
either the morphological right or the morphological left ventricle,
38
although normally constituted, is too small as to support the systemic
or the pulmonary circulation, such as hypoplastic left heart syndrome
(HLHS), pulmonary atresia with intact ventricular septum (PA-IVS)
and hypoplastic right ventricle, or severely unbalanced AVSD.
Other hearts with complex circulatory patterns may be deemed to be
•
functionally univentricular and hence better suited for surgical repair
by means of construction of the Fontan circulation.
18 What is the phenotypic feature of tricuspid atresia?
Atresia, when defined literally, is either the absence or abnormal
•
closure of a bodily communication.
Both of these phenotypes are to be found in the setting of tricuspid
•
atresia, since the lesion can be produced either by an imperforate
tricuspid valve or by the absence of the right atrioventricular
connection in the setting of a usual atrial arrangement with the left
atrium connected to a dominant left ventricle (Figure 27).
The arrangement with the absence of the right atrioventricular
•
connection is by far the commonest variant found in patients with
tricuspid atresia. By virtue of the absence of the right atrioventricular
connection, the right ventricle in this setting is incomplete, since it
lacks its inlet component.
The arrangement as seen in postnatal life reflects the situation as
•
seen during the initial stages of normal development, when the
atrioventricular canal is supported exclusively by the developing
A
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Right atrium
1 Congenital cardiac anatomy
Left atrium
Left ventricle
Imperforate tricuspid valve
B
Left atrium
Right atrium
Absent AV connection
Hypoplastic right ventricle
Left ventricle
Incomplete right ventricle
Figure 27. Macroscopic images demonstrating the difference between
tricuspid atresia produced by: A) an imperforate valve; and B) absence
of the right atrioventricular (AV) connection.
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