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Conotruncal defects occur about 5-6 weeks after conception, when the heart is essentially an S-shaped tube with upper and lower bulges. A dividing wall bisects the lower heart areacalled the conotruncusresulting in 2 ventricles (pumping chambers) and 2 major blood vessels, the pulmonary artery (leading to the lungs) and the aorta (leading to the rest of the body).

All conotruncal defects cause improper circulation of oxygenated and depleted blood. Affected infants require complex open heart surgery; many die from their heart defects or other birth defects. Among chromosomally normal infants, conotruncal heart defects occur in 7.3 per 10,000 livebirths and fetal deaths. They are more frequent in males than females.

The most common types are:

bullet Double outlet right ventricle (0.4 per 10,000): pulmonary artery and aorta both arise from the right side of the heart.
bullet Pulmonary atresia (0.3 per 10,000): an absent valve at the entrance to the pulmonary artery blocks blood flow to the lungs.
bullet Tetralogy of Fallot (2.9 per 10,000 births): its 4 components are underdeveloped right heart, hole between the ventricles, overriding aorta and underdeveloped pulmonary artery.
bullet Transposition of the great vessels (2.6 per 10,000 births): reversal of the main blood vessels leading from the heart.
bullet Truncus arteriosus (0.9 per 10,000 births): a single blood vessel replaces the pulmonary artery and aorta.

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WHY STUDY CONOTRUNCAL DEFECTS?

Heart development is a relatively long and complex process; specific defects may arise at different developmental stages or through different pathways. When studying birth defects, it's important to group embryologically similar conditions and have precise diagnosis. For this reason, the California Birth Defects Monitoring Program focuses its heart research on conotruncal defects. These serious conditions are not likely to be overlooked or misclassified.

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