Hypoplastic Left Heart Syndrome

Anatomy & Physiology

Full features of HLHS include small LA, LV & ascending aorta, atretic mitral and aortic valves with retrograde filling of ascending aorta. Entero-viruses have been detected in postmortem specimens.

The pulmonary venous return cannot pass through the mitral valve into the LV as it is atretic and must therefore pass through an atrial defect into the right atrium, mixing with systemic venous return and passing into the aorta via the right ventricle, pulmonary artery and patent ductus. It is a duct dependent lesion.

Presentation

Presents as collapsed neonate when duct closes. Usually acidotic and pulseless with signs of cardiac failure. The precordium is active and there are no murmurs.

Investigations

The heart is usually big on the chest x-ray. The ECG may be surprisingly normal.

Echocardiography enables the diagnosis to be made easily. The anatomical features of a small LV and aorta are usually easy to demonstrate (even in the fetus).

Great vessels - echocardiogram

The PDA supplies the aorta (right) and there is reverse flow around the aortic arch towards the root to feed the coronary arteries (far right - red flow).

Natural History

It is the commonest cause of death from cardiac disease in the West although much less common amongst the Asian population. The vast majority succumb within the first month of life.

Management

Resuscitate and give prostaglandin. Most require ventilation and often inotropic support. The ventilatory principles for patients with a single ventricle are different to those with a biventricular circulation. Because the ventricular output passes to both the pulmonary and systemic circulations the flows to each circulation is interdependent. The relative vascular resistance in the pulmonary and systemic beds determines the flow to each circulation. Manipulation of the pulmonary resistance by adjusting the pCO₂ and FiO₂ enables the systemic and pulmonary circulations to be controlled.

Once the diagnosis has been made careful counseling of parents re the management options (surgical approach or palliative care) is necessary given the outcome of this condition.

When a surgical approach is undertaken the initial operation is a Norwood procedure once the baby is stable. This is then followed by a cavo-pulmonary shunt at 6-12 months of age and completion to Fontan at 3 - 5 years of age.

Prognosis

The operative mortality for the Norwood procedure and subsequent construction of the Fontan circulation varies from institution to institution but sadly less than 50% of children will survive to school age with a good quality of life. The long term prognosis remains guarded as these children have a morphological right ventricle supplying the systemic circulation.

This page was last edited 16/2/2004

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