by Alicia M Prater PhD

Created on: September 18, 2009   Last Updated: February 14, 2010

A congenital defect is one that is present from birth, and there are a variety of defects that can occur in the heart tissue or heart valves due to improper fetal growth, as well as problems with the closure of fetal vessels after birth. Congenital heart defects are usually recognized in infants shortly after birth because of the importance of circulation in sustaining life, and the change in palor that presents with cyanotic (lack of oxygen) defects. The

Merck Manual for Healthcare Professionals reports that 1 of every 120 live births has a congenital heart defect, and they tend to form in the first 10 weeks of fetal life. Some of the more common congenital heart defects are discussed below.

Left-to-Right Shunt

A left-to-right shunt allows blood inside the heart to bypass being pumped through the aorta (to the body), but instead returns to the right side of the heart. This causes some of the oxygenated blood to continue circulating in the heart and pulmonary vessels instead of the body. The most common type of congenital heart disease is a left-to-right shunt caused by holes in the ventricular septum (the tissue between the left and right ventricles) due to defects in the membrane along the intraventricular ridge. The holes are sometimes asymptomatic and usually close spontaneously throughout childhood.

Another left-to-right shunt is the improper closing of the foramen ovale. The fetal heart is not identical to the heart of a child or adult. Because a fetus receives oxygen from the mother's circulation and does not use its lungs, the fetal circulation does not pass through the pulmonary vessels. Instead, a hole in the atrial septum, the wall between the right and left atria, allows blood to pass directly from the right side of the heart to the left side of the heart - the hole is called the foramen ovale. When a baby takes its first breath of air outside the womb, the pressure causes a flap to close over the foramen ovale. If this closure does not occur, or if it is incomplete, blood is able to seep through the atrial septal defect, resulting in a shunt.

The size of the shunt will determine if, and to what extent, symptoms occur. The pressure within the pulmonary artery or ventricle may increase, depending on the type of left-to-right shunt. High pressure in the ventricle could result in ventricular hypertrophy. High pressure in the pulmonary vessels can affect lung function.

Right-to-Left Shunt

A right-to-left shunt bypasses the pulmonary circulation and

• 1
• 2
• Next Page >>