The ventriculoarterial connection is termed concordant when the morphologically
right ventricle aligns with the pulmonary artery, and when the morphologically left
ventricle aligns with the aorta. Concordant ventriculoarterial connections exist with both
normally related great arteries, such as in the tetralogy of Fallot or double outlet right ventricle, or with
abnormally related great arteries as would occur in congenitally corrected, or L-looped,
transposition of the great arteries. Ventriculoarterial connections are discordant
when the morphologically right ventricle is aligned with the aorta, and the left ventricle
is aligned with the pulmonary artery, as would typically occur in D-looped transposition of the great
arteries. Other types of abnormal ventriculoarterial connection include truncus
arteriosus, the tetralogy of Fallot, double-outlet right ventricle and double-outlet left
ventricle.
To determine the type of ventriculoarterial connection, it is necessary to know the
ventricular morphology and the number and arrangement of the great arteries. There are
four possibilities. The first two exist when each of two ventricles gives rise to its own
arterial trunk. This can be when the great arteries, aortic and pulmonary, arise either
from the appropriate ventricle (concordant ventriculoarterial connections) or from an
inappropriate ventricle (discordant connections). The third pattern exists when both great
arteries arise from a single ventricle. This is termed double outlet ventricle, which can
be a morphologically right, left, or an indeterminate ventricle. The final pattern exists
when only a single arterial trunk arises from the ventricular mass, termed single outlet
of the heart. There are four variants to this form of ventriculoarterial connection,
including that in which the single outlet is a common trunk, a main pulmonary
artery in the setting of aortic atresia, an aortic trunk in the presence of
pulmonary atresia, or a solitary arterial trunk when there is absence of the
central pulmonary arteries. When there is a single outlet, the solitary trunk usually
over-rides the ventricular septum when there are two ventricles, but less commonly it may
be exclusively connected to one or the other ventricle irrespective of the morphological
nature of that ventricle. When there is a solitary ventricle then, of necessity, the trunk
will be exclusively connected to it.
Since the arterial valves possess no tension apparatus, unlike the ventricular valves,
they cannot straddle. All the other modes of connection, however, can occur at the
ventriculoarterial junction. Thus, there may be a common arterial valve which,
nonetheless, can exist only in the presence of a common arterial trunk. Either the aortic
or the pulmonary valve can be imperforate. Such imperforate arterial valves can be found
in association with concordant, discordant or double outlet connections. They produce one
type of arterial valve atresia, but this is to be distinguished from the other type found
with single outlet of the heart. The distinguishing feature is that there must be a
potential ventriculoarterial connection present in order to confirm an imperforate. valve,
or muscular atresia with a blind-ending trunk connected to the underlying ventricle. The
diagnosis of single outlet via an aortic or a main pulmonary artery is made only when it
is not possible to trace the atretic arterial trunk to a ventricular origin. The other
mode of connection is over-riding of an arterial valve. Over-riding has already been
referred to in the setting of single outlet, where the ventricular origin of the solitary
trunk must be described to provide complete categorization of the connection. When one of
two arterial valves, or rarely both, over-rides the septum, then, as with over-riding
ventricular valves, the precise morphology of the over-riding junction determines the
connection present. This is decided using the '50% rule'. The mechanics of determining the
degree of over-ride depend upon projecting the chord subtended by the ventricular septum
onto the circle of the over-riding valve. When the '50% rule' is applied in the setting of
double outlet ventricle, it is possible to broaden the definition of the condition to more
than half of both arterial valves connected to the same ventricle.
The situs of the ventriculoarterial connections is based on the
relationships of the ventricles to the great arteries, and are designated as S (normal
sidedness, concordant connection), I (inverted sidedness, concordant connection), D
(normal sidedness, abnormal connection), L (inverted sidedness, abnormal connection), and
A (ambiguous). Hence, S-ventriculoarterial connection occurs in the normal heart, whereas
an I-ventriculoarterial connection occurs in the totally inverted heart. The remaining
designations (D, L, and A) are used in the presence of discordant or abnormal
ventriculoarterial connections, and refer to the position of the aortic valve relative to
the pulmonary valve. A ventriculoarterial D-malposition therefore indicates that there
is an abnormal ventriculoarterial connection, and that the aortic valve is located to the
right of the pulmonary valve (the usual arrangement of the arterial valves). A
ventriculoarterial L-malposition indicates an abnormal ventriculoarterial connection, but
that that the aortic valve is left-sided. A ventriculoarterial A-malposition indicates an
abnormal ventriculoarterial connection, but that the right-left location of the aortic
valve relative to the pulmonary valve is equivocal. It is worth studying the use of
'connection' versus 'malposition' in the above paragraph.
Some examples using this method include:
- the normal heart is designated as {S,D,S}, meaning that the venoatrial connection
is normal, the ventricles are D-looped, and the ventriculoarterial connection is normal.
- The totally inverted heart is designated {I,L,I}, meaning that the venoatrial
connection is concordant but inverted, the ventricles are L-looped (hence the right
ventricle is left-sided and arranged from left-to-right, and the right ventricular valve
is left-sided), and that the ventriculoarterial connection is concordant but inverted
(right ventricle ® pulmonary artery, left ventricle ® aorta, but the aortic valve is left-sided).
- Simple transposition of the great
arteries is designated as {S,D,D} TGA meaning that there is venoatrial situs solitus,
the ventricles are D-looped, there is an abnormal ventriculoarterial connection, and the
aortic valve is located to the right of the pulmonary valve. The 'TGA' portion clarifies
the type of abnormal ventriculoarterial connection, and distinguishes {S,D,D} TGA from
closely related defects such as {S,D,D} TGA, VSD and {S,D,D} DORV.
- Congenitally corrected transposition
of the great arteries is designated as {S,L,L} TGA, meaning that the venoatrial
connection is normal and right-sided, the ventricles are L-looped, there is
atrioventricular discordance, there is an abnormal ventriculoarterial connection, and the
aortic valve left-sided.
The same steps used in describing the atrioventricular junction are used at the
ventriculoarterial junction, looking at the type and mode of connection, but supplementing
this information with considerations of infundibular morphology and the relationships of
the great arteries. |