Truncus Arteriosus
Definition
This type of congenital defect occurs when a single great artery, either pulmonary artery or aorta leaves the base of the heart and gives rise to coronary, pulmonary, and systemic arteries. Only one semilunar valve is present in this condition. The resulting truncal valve is quadricuspid in 50% of all cases and very rarely pentacuspid or hexacuspid. There are five different types of truncus arteriosus.
I. PA and Ascending aorta split up after common origin.
II. PA does not exist. Both pulmonaries arise from posterior truncus arteriosus.
III. PA does not exist. Both pulmonaries arise from lateral truncus arteriosus.
IV. Descending aorta gives rise to both pulmonary arteries, or there is a total absence of PA abd descending aorta gives rise to hypertrophied bronchial arteries.
V. Also known as pseudotruncus. A variation of Tetralogy of Fallot. Bronchial collateral vessel enlargement is necessary for survival.
Pathophysiology
An obligatory mixing of systemic and pulmonary blood occurs in all cases due to the absence of a separation between two circulations. Increased pulmonary resistance tends to direct the flow towards the systemic circulation. Pulmonary artery saturation is usually 10% less than that of the systemic circulation. If the condition is uncorrected the child will develop congestive heart failure (CHF) secondary to pulmonary overload.
Hemodynamics
VSD is often present in order for a single arterial trunk to receive the output from both ventricles. As a result of an abnormal truncal valve its function is often incompetent (usually regurgitant). When a main pulmonary artery arises from the truncus, the blood flow through the lungs is excessive, systemic oxygen saturation is high and left heart is overloaded. Eventually, pulmonary vascular resistance (PVR) rises and pulmonary blood flow falls, cyanosis increases and left side volume overload decreases.
Clinical Manifestations
The first sign may be that of a mild cyanosis, however, this may dissapear with decreasing PVR. CHF may occur secondary to pulmonary overload.
Surgical and Medical Interventions
Medical management is limited to placing children on digitalis and diuretics until they reach 4-6 months of age.
Surgical interventions may consist of removing pulmonary arteries from the truncal artery. If truncal valve is not competent it must be replaced with a valved homograft in aortic position (this conduit will have to be replaced as child grows). VSD is closed at this time.
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