Defecto septal ventricular

With ventricular septal defects, “ventricular” refers to the heart’s two lower chambers, called the ventricles; “septal” refers to the septum, which is the wall that separates them; while “defect” means there’s an opening that shouldn’t be there. So, a ventricular septal defect is a congenital heart defect characterized by an abnormal gap in the wall separating the ventricles.

To understand how this opening forms, we need to review how the ventricular septum develops during fetal life. Early during heart development, the left ventricle starts as a primitive ventricle, while the right ventricle develops from the bulbus cordis. Around the fourth week of development, a muscular ridge begins growing upward from the heart’s apex, eventually fusing with a membranous wall coming down from the endocardial cushions. This fusion divides the lower half of the heart into the left and right ventricles.

If these walls don’t fuse correctly, a gap is left between the two chambers. This opening is what we call a ventricular septal defect, or VSD. VSDs are actually one of the most common congenital heart defects in babies, and they tend to show up even more often in fetal alcohol syndrome and Down syndrome.

Now, we classify VSDs based on the location of this opening. Most VSDs occur in the upper membranous portion of the septum, which happens to be the last part to close during fetal development. On the flip side, muscular VSDs are less common but more likely to close on their own. In some cases, the defect might arise in the inlet portion of the septum, near the tricuspid and mitral valves, or in the outlet portion, close to where blood exits the ventricles toward the great vessels.

During fetal life, VSDs usually don’t cause problems because the pressure in the right and left ventricles is pretty much the same, and that’s all thanks to how fetal circulation works. In the fetus, the lungs are collapsed and filled with fluid, so the pulmonary vessels are squeezed tight. Because of this high resistance in the pulmonary vessels, the right ventricle is unable to pump blood into the lungs. Instead, the blood takes a detour through two fetal shunts. First, there’s the foramen ovale, a small opening that allows blood to flow directly from the right atrium to the left atrium. Then, there’s the ductus arteriosus, a vessel that connects the pulmonary artery to the aorta. These shunts allow the blood from the right ventricle to bypass pulmonary circulation and flow directly into the systemic circulation.