Hypoplastic Left Heart Syndrome
Definition
Hypoplastic Left Heart Syndrome (LHH) is an underdevelopment, hypoplasia, of left atrium (LA), mitral valve (MV), left ventricle (LV), and aortic valve (AV).
There are two types of LHH:
Type I:
Hypoplastic LV receives a patent but hypoplastic MV and an atric AV.
Type II:
Most extreme among two types, also more prevalent. Consists of hypoplastic left heart, both MV and AV are atretic, and LV is absent or nearly so.
LHH accounts for 7.5% of congenital heart disease, average lifespan of infants is 5-14 days, 95% die within the first month.
Pathoanatomy
Type I:
Small LV cavity, atretic outflow and patent inflow. PDA is present providing the only channel of blood flow into sytemic circulation. The only outlet from the obstructed LA is through interatrial communication, usually patent foramed ovale. RV mass would increase because it is the only driving force for systemic and pulmonary circulations.
Type II:
Morphologic remains of atretic MV, connects floor of LA to rudimentary LV. LV outflow and inflow are atretic, ventricular cavity is extremely small. Ventriculocoronary arterial connections do not develop. Pure RV hypertrophy is present.
Physiology and Hemodynamics
Determined chiefly by PDA, PVR, and condition of interatrial septum. When PVR is low circulation from the pulmonary trunk through ductus results in an increase of pulmonary arterial blood flow. Large volume of oxygenated blood is available for mixing with caval blood in RA so systemic arterial oxygen saturation is high. A decrease in PVR would result in preferential flow from pulmonary trunk through ductus into the lungs with a fall in systemic flow, may produce a shock-like state.
Clinical Manifestations
Hypoxemia and hypotension are common, associated with hypoxic-ischemic cerebral lesions and intracranial hemmorrage. Increased incidence of major and minor congenital central nervous system abnormalities, may occur in trisomy 21.
Surgical Interventions
Full or modified Fontan procedures may be performed. A bidirectional cavopulmonary shunt (SVC to both pulmonaries) may also be utilized.
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