and Structural Heart Disease
|Hypoplasia of the left heart structures, in its
extreme form, the mitral and aortic valves are atretic, left
ventricle is hypoplastic and the ascending aorta is no wider
than the coronary arteries.
|This is the 13th most common congenital heart
disease. It occurs in 0.05-0.25/1,000 live births (1.5% of all congenital
heart disease at all ages).
|HLH is most probably due to
reduced blood flow from the ductus venosus to the left heart, possibly due
to small atrial communication.
The left ventricle is small with or without
mitral atresia and with or without aortic valve atresia.
The ascending aorta may be as small as 2 mm
but enough to supply coronary arteries in a retrograde fashion. The PDA is
large shunting right-to-left. Babies are not born with coarctation but it
frequently develops. A patent foramen ovale could be small or even closed.
The right ventricle provides blood to two
pulmonary arteries and to aorta through the PDA. Pulmonary blood flow
depends upon pulmonary vascular resistance which in turn depends upon
patent foramen ovale. When patent foramen ovale is restrictive left atrial
pressure will be elevated causing increased pulmonary vascular resistance
and less pulmonary blood flow. The more the pulmonary blood flow the
better is the systemic oxygen saturation. Although hypoplastic left heart
is the most lethal congenital heart disease, the cardiac anatomy is
adequate for intrauterine life. The atrial septum is thick and this may be
due to increased left atrial pressure in utero leading to LA hypertrophy
or this might be the primary pathology causing decreased right-to-left
shunting in utero at the PFO level leading to hypoplasia of the left
Coronary and head blood flow may be decreased
after birth due to coarctation of the aorta secondary to ductal tissue in
the aortic arch.
At birth babies do well due to increased
pulmonary vascular resistance therefore adequate systemic flow once
pulmonary vascular resistance decreases will cause increase in pulmonary
blood flow and decrease in systemic blood flow leading to shock. After
birth as the pulmonary blood flow increased this will increased the load
on the right ventricle. In addition, the coronary blood flow will decrease
as the PA is restricted causing RV ischemia. Prostaglandin by reopening
the patent ductus arteriosus will decrease LV pressure and improve
coronary circulation, however, pulmonary blood flow will increase because
of PGE’s pulmonary vasodilatory effect.
|Poor cardiac output after birth will lead to
poor renal perfusion and increase in intravenous volume as well as in
hyperkalemia. These child will develop a poor appetite and this will lead
to hypoglycemia. The increase in intravascular volume, hyperkalemia and
hypoglycemia coupled with decreased coronary blood flow due to the
restriction of the PDA will lead to myocardial injury.
|Due to hypoplasia of the LV, there will be
reduced LV forces, resulting in right axis deviation and RVH
pattern. The R wave progression in the chest leads is also abnormal,
with prominent S wave in left chest leads.
|Enlarged right heart and
reduced LV mass resulting in lack of distinct LV apex.
Mediastinum may be narrow due to hypoplasia of the ascending aorta.
These babies typically present with acidosis
and shock. They should be intubated and mechanically ventilated with
correction of acidosis. Prostaglandin is started to increase the pulmonary
As the ductus arteriosus is opened by
Prostaglandin the pulmonary blood flow will increase significantly
particularly that Prostaglandin is a vasodilation therefore this should be
controlled by increasing the pulmonary vascular resistance. This could be
achieved by hypercarbia, controlled acidosis and mild hypoxia. Hypercarbia
and respiratory incidence could be achieved by providing subambient oxygen
through mixing carbon dioxide or nitrogen with room air.
Surgical management includes the Norwood
procedure or cardiac transplantation.
The Norwood procedure includes an initial
palliative procedure followed by the Fontan procedure. Palliation includes
using of the pulmonary valve and proximal MPA as neo-aorta and neo-aorta
by ligating the distal main pulmonary artery and connecting the proximal
main pulmonary artery to the aortic arch. This will improve the systemic
blood flow and then the pulmonary arteries are fed by a 3-1/2 to 4 mm
systemic to pulmonary arterial shunt. In addition, the atrial septum is
removed surgically and the PDA is ligated. The pulmonary veins may develop
progressive stenosis, the etiology is unclear. Tricuspid regurgitation my
develop and become progressive which is of significance since the right
ventricle is the systemic ventricle. Coarctation of the aorta is common in
those who survive the first step of palliation because of residual ductal
tissue. Therefore, at the time of palliation the area of coarctation could
be bypassed by a homograft. The first stage of Norwood procedure is
performed at 1-2 weeks of age and the second stage at about 2 years of
age. Alternatively, three stages could be done. The first a Norwood and
systemic to pulmonary arterial shunt, the second at about 6 months a bi-directional
Glenn and the third stage would take down the systemic to pulmonary
arterial shunt at about 18-24 months where the Fontan is completed by
connecting the inferior vena cava to the pulmonary arterial circulation.