Ventricular septal defect
In most cases, ventricular septal defects are defects of the (membranous/muscular) portion of the interventricular septum.
USMLE® Step 1 style questions USMLE
USMLE® Step 2 style questions USMLE
A 33-year-old G2P1 woman comes to the office because of poor diabetic control. She is currently at 18 weeks' gestation and admits to having poor control of her type I diabetes before becoming pregnant. Family history is non-contributory. Examination shows a pregnant woman with a fundal height of 20 cm (7.9 in). An abdominal ultrasound is ordered. Which of the following is the most likely congenital abnormality shown on the ultrasound?
If you look at the heart, you’ve got the right and left atria up top, and the right and left ventricles down below. Each of these pairs is separated by a wall called the septum. A ventricular septal defect is when the lower wall, the ventricular septum, has a gap in it after development.
The septum is formed during development as a 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: now there are two separate chambers. However, If these tissues don’t fuse, then a gap is left between the two chambers; this is 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 overall most common congenital defect. However, 30 to 50% of VSDs can spontaneously close during childhood, which makes ventricular defects less common among adults. VSDs are associated with fetal alcohol syndrome and Down syndrome, and are often associated with other cardiac deformities.
All right, so let’s check out what happens with blood flow, now that there’s this opening between the two ventricles. We’ll switch to this super-duper simplified image of the heart, just because it’s easier to show what’s going on with blood flow. So, deoxygenated blood comes from the body to the right atrium, and then flows down into the right ventricle; here, it can now either be pumped out to the lungs as normal, or pop over to the left ventricle. Because the pressure on the left side of the heart is actually higher than on the right, and because blood likes to flow from high pressure to low pressure, it actually prefers to just keep going into the lungs. When oxygenated blood comes back from the lungs and enters the left atrium, and then the left ventricle, 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 the blood is in the left ventricle, which has higher pressure, some of the blood flows over to the lower pressure right ventricle; thus, now there’s a left-to-right shunt through which oxygenated blood takes an extra trip to the lungs.
Because there’s more oxygenated blood over here, patients will have increased oxygen saturation in the right ventricle and pulmonary artery. Also, the blood flowing through a VSD can be heard as a holosystolic murmur at the lower left sternal border.