A ventricular septal defect (VSD) refers to a hole in the ventricular septum, the wall dividing the left and right ventricles of the heart. VSDs are the most common congenital cardiac anomalies. They are found in30-60% of all newborns with a congenital heart defect, or about 2-6 per 1000 births. During heart formation, when the heart begins life as a hollow tube, it begins to partition, forming septa. If this does not occur properly it can lead to an opening being left within the ventricular septum.
As noted above, during ventricular contraction some of the blood from the left ventricle is forced into the right ventricle from where it enters the lungs through the pulmonary arteries and then reenters the left ventricle via the pulmonary veins and left atrium. This refluxing of blood causes volume overload on the left ventricle. This increased blood volume also increases pressure in the right ventricle eventually causing pulmonary hypertension with its associated symptoms. This effect is more noticeable in those with larger defects, who may present with shortness of breath, poor feeding and failure to thrive in infancy.
Because structural cardiac anomalies are estimated to occur in 8 of every 1,000 live births, it is imperative they be discovered before birth. Cardiovascular anomalies, such as VSD, are frequently associated with other congenital anomalies because the heart is among the last organs to develop completely in the embryo. The guidelines for routine prenatal evaluation of both the American College of Radiology and the American Institute of Ultrasound in Medicine require an evaluation of the fetal heart. To not do so, may be consistent with medical negligence or medical malpractice.
The ultrasound view that is most commonly used is the four-chamber view of the heart. This allows for the assessment of abnormalities involving both rights and left ventricles. Normally, both ventricles are approximately the same size. The left ventricle is posterior and to the left of the right ventricle. The wall between them, known as the interventricular septum separates the right ventricle from the left ventricle. A normal septum goes from the cardiac apex to the atrial septum. Formation of the interventricular septum begins at approximately 28 days gestation. A VSD results from maldevelopment of the embryonic septum.
A large VSD is easily diagnosed on the four-chamber view alone. However, color Doppler ultrasonography may be needed to demonstrate smaller defects, and some really small defects may not be detected until after birth. However, most of these close spontaneously. Fetal position is a major factor in the detection of VSD. For an accurate diagnosis, it is critical that the ultrasound technician positions the transducer so the ultrasound beam is correctly directed relative to the septum. Not only can a VSD be missed, but a pseudo-VSD may result if performed incorrectly.
A small ventricular septal defect may never cause any problems. Larger defects can cause a wide range of disabilities, from mild to life-threatening. If pulmonary hypertension develops due to a large ventricular septal defect that goes untreated, over time, permanent damage to the lung arteries develops and pulmonary hypertension becomes irreversible. This complication is known as Eisenmenger’s syndrome and may occur in early childhood, or it can develop slowly over many years. Other complications that occur are heart failure, endocarditis, stroke, and heart arrhythmias which can lead to fatal complications. Becoming pregnant is also of concern due to the additional risks of pregnancy to women with VSDs undetected before birth and throughout childhood.
Though no treatment is necessary for small VSDs, larger VSDs demand certain precautions are taken, often with the baby being born in a tertiary care center and directly placed into the care of a pediatric cardiologist to determine if medical or surgical therapy is necessary to prevent the complications that will occur. That is why it is imperative that the diagnosis of VSD be made prior to birth.