Hemodynamics of the described lesion:
Aortic valve atresia (AVA) with IAA is incompatible with life unless
blood flow is provided to the ascending aorta and coronary arteries from
bilateral ductus arteriosus or from pulmonary artery through an
aortopulmonary window or from descending aorta through collaterals. In
the absence of the above source of blood flow, the only possible way for
coronary arteries perfusion as illustrated in this case (Figure
3 A &B) is through vessels (left carotid and left vertebral artery)
arising from the descending aorta flowing to the circle of Willis to
perfume the brain and then the hypoplastic aorta and the coronary
arteries through retrograde flow via the right carotid artery and right
vertebral artery. AVA with IAA type A and AVA with IAA type B can never
survive. In the AVA-type B IAA, the only flow to the circle of Willis is
the left vertebral artery, which will be insufficient to perfuse
together the brain and the coronary arteries.(1) The hemodynamic effects
of left side cardiac abnormalities are usually compensated during fetal
life, as the fetal circulation allows for the left side of the heart to
be bypassed. Once a baby with hypoplastic left heart syndrome(HLHS)
takes its first breath, if the left side structures are inadequate (as
in this case mitral valve atresia and absent LV) the pulmonary venous
return must shunt across the atrial septum to the right heart, allowing
the egress of blood from heart to the lungs via main pulmonary artery
and to the systemic circulation via the patent ductus arteriosus. If the
atrial septum is intact or restrictive, it leads to critical left atrial
hypertension, pulmonary congestion and severe hypoxemia, creating an
emergent situation that requires immediate atrial septectomy. This
condition will lead to maldevelopment of pulmonary vasculature
[lymphatic dilatation, pulmonary venous wall thickening and fibrosis
(venous arterialisation)], an appearance termed as nutmeg lung.(2)
HLHS with intact atrial septum have the highest risk for mortality. (3)
Maldevelopment of the pulmonary vasculature (nutmeg lung appearance) is
associated with increased mortality.(4)