Congenital heart diseases are abnormalities of the heart and/or great vessels present at birth. They are not all that uncommon: 1% of live births in this country has a congenital heart defect! The clinical spectrum is broad. Some congenital heart diseases cause death in the perinatal period; others are so mild that there are only minimal symptoms, even in adulthood.
Something happens in embryogenesis at the time of heart development (weeks 3-8) – but the actual cause can be traced only 10% of the time. Of the known causes, infections (like rubella) and genetic disorders (like trisomy 13) are the most common.
You can divide congenital heart defects into two broad groups: those that cause shunts (abnormal communication between chambers or vessels) and those that cause obstructions (narrowed chambers, valves, or major vessels). Shunts are more common than obstructions; the more common of these are atrial septal defects, ventricular septal defects, patent ductus arteriosus, and tetralogy of Fallot. The most common obstruction is aortic coarctation. Let’s take a really quick look at these defects.
Atrial septal defects
In this type of congenital heart disease, there is a hole between the two atria. Initially, this causes a left-to-right shunt. Left to right shunts, in general, are pretty well tolerated, and that’s the case for ASD too. However, over time, especially if the defect is large, pulmonary vessels can become annoyed by all that extra blood volume they are exposed to – and the pressure in the lungs goes up (due to vessel constriction and fibrous tissue deposition). So the pressure on the right side goes up, and eventually it can even exceed the pressure on the left, leading to a reversal of the shunt. This is called Eisenmenger Syndrome. This is not a good thing, because it can lead to heart failure, irreversible pulmonary vascular disease, and paradoxical embolism (where blood clots from the heart go to the systemic, rather than pulmonary, circulation).
Ventricular septal defect
This is the most common congenital cardiac anomaly, and it’s just what the name says: a hole between the two ventricles. Small VSDs are generally asymptomatic; large VSD cause big left-to-right shunt, which may become right-to-left (as described above). Most close spontaneously in childhood.
Patent ductus arteriosus
The ductus arteriosus is a normal connection between the pulmonary artery and the aorta that exists in fetal life to allow most of the blood to bypass the unoxygenated lungs (this helps the left ventricle get stronger). The ductus normally closes spontaneously by day 1 or 2 of life; if it remains open, then you can get a left to right shunt. Most of the time PDAs are asymptomatic, but if they big enough, they can eventually lead to Eisenmenger syndrome.
Tetralogy of Fallot
This defect is an example (the most common example) of a right-to-left shunt. Right-to-left shunts in general present with cyanosis at birth, because poorly-oxygenated blood from the right heart gets mixed into the arterial circulation. Patients can get clubbing of the fingertips and erythrocytosis as a result. Tetralogy of Fallot has four features: VSD, obstruction to the right ventricular outflow tract, an aorta that overrides the VSD, and right ventricular hypertrophy. Even untreated, though, many patients survive into adult life. It all depends on the severity of the pulmonary outflow obstruction.
Aortic coarctation
“Coarctation” means “narrowing” – so aortic coarctation means narrowing of the aorta. There are two forms: infantile (in which the narrowing occurs proximal to the ductus arteriosus) and adult (in which the narrowing occurs distal to the ligamentum arteriosum). In the infantile form, there is delivery of poorly-oxygenated blood through the ductus, which leads to cyanosis in the lower half of body. The femoral pulses are generally weaker than those of the upper extremities. This is a severe abnormality; these babies need intervention or they may not survive the neonatal period. The adult form is usually asymptomatic, and the disease may go unrecognized into adult life. When there are symptoms, they consist of upper extremity hypertension (due to poor perfusion of kidneys) but weak pulses and lower blood pressure in lower extremities.
Image credit: qthomasbower (http://www.flickr.com/photos/qthomasbower/3470650293/), under cc license.
Recent Comments