Wikipedia:Osmosis/Ventricular septal defect



Author: Tanner Marshall, MS

Editor: Rishi Desai, MD, MPH, Tanner Marshall, MS

If you look at the heart, you’ve got your right and left atrium up top, and right and left ventricles down low. Each of these pairs is separated by a wall, called a septum. A ventricular septal defect is when this lower wall—the ventricular septum—has a gap in it after development.

The septum is formed during development as this muscular ridge of tissue grows upward from the apex, or the tip, and then fuses with a thinner membranous region coming down from the endocardial cushions. Voila—two separate chambers. If these don’t fuse though, then a gap is left between the two chambers, in other words, a ventricular septal defect, or VSD. The majority of cases are caused by a defect in the membranous portion of the septum.

Among babies, VSDs are actually the most common congenital defect overall, but 30 to 50% of VSDs can spontaneously close during childhood, which makes ventricular defects less common with adults. VSDs are associated with fetal alcohol syndrome and Down syndrome, and often are associated with other cardiac deformities as well.

Alright so now let’s check out what happens with blood flow, now that there’s this opening between the two ventricles. I’m actually going to switch to this super duper simplified heart instead, just because it’s easier to show what’s going on with blood flow. Alright, so deoxygenated blood comes from the body to the right atrium, and then flows down into the right ventricle, where now it can either be pumped out to the lungs, as normal, or pop over to the left ventricle. Since the pressure on the left side of the heart’s actually higher than on the right, and blood likes to flow from high pressure to low pressure, it actually prefers to just keep going on to the lungs. When oxygenated blood comes back from the lungs to the left atrium, and then left ventricle. Now again, it’s got two choices, it can either be pumped out to the body, or flow over to the right ventricle through the gap. Since now it’s in the left ventricle which has higher pressure, some of the blood flows over to the lower pressure right ventricle, so a left-to-right shunt has been set up, where oxygenated blood takes an extra trip to the lungs. Since there’s more oxygenated blood over here, patients will have an increased oxygen saturation in the right ventricle and pulmonary artery.

Also, that blood flowing through a VSD can be heard as a holosystolic murmur at the lower left sternal border.

If it’s a small VSD, it might be asymptomatic. As the size of the VSD increases, though, symptoms tend to get more severe and present earlier on in life. But what sort of symptoms? Well as blood is shunted to the right side, blood volume increases on the right side, might lead patients to develop pulmonary hypertension, or higher pressures on the pulmonary side. If pressure increases to a point where the right side’s more than the left side, then the direction of blood flow through the VSD can switch from being left-to-right to right-to-left, a condition known as Eisenmenger syndrome. Now, deoxygenated blood is escaping out to the systemic circulation, and being pumped out to the whole body via the aorta. This essentially means that less oxygen’s being delivered to the tissues, which definitely isn’t good. Patients can present with cyanosis, specifically it can appear as bluish skin in certain areas like around the lips or the fingertips.

Due to the severity of these complications with larger defects, surgical closure of the VSD might be needed.