Congenital Heart Defects Flashcards
What is the incidence of congenital heart defects and what are the most common ones?
Congenital heart defects are common, with an incidence of 6-8 per 1,000 births. The most common heart defects are Ventricular Septal Defects (VSD), followed by Atrial Septal Defects (ASD).
What is an Atrial Septal Defect?
An ASD is an opening in the septum between the two atria, which persists following birth. They have an incidence of 67 in 100,000 live births.
The foramen ovale exists to prenatally permit right left shunting of oxygenated blood and is designed to close promptly after birth. Failure of it to close, allows blood to continue to flow between the two atria postnatally. Because left atrial pressure > right atrial pressure, flow will be mainly from left to right, meaning no mixing of deoxygenated blood with the oxygenated blood being pumped around the circulation.
ASDs can occur almost anywhere along the septum, but the most common site is the foramen ovale (Ostium secundum ASD). An ostium primum ASD occurs at the inferior part of the septum, and is less common.
What is a Patent Foramen Ovale
PFOs are not a true ASD. PFOs may be present in ~20% of the population and are generally clinically silent, since the higher left atrial pressure causes functional closure of the flap valve.
A PFO may however be the route by which a venous embolism reaches the systemic circulation if pressure on the right side of the heart increases even transiently. This is called a paradoxical embolism.
What is a Ventricular Septal Defect?
VSDs are an opening in the Interventricular Septum. This most commonly occurs in the membranous portion of the septum, but can occur at any point. Since left ventricular pressure is much higher than right, blood will flow from left to right.
What is a Patent Ductus Arteriosus?
The Ductus Arteriosus is a vessel that exists in the foetus to shunt blood from the pulmonary artery to the aorta before the lungs are functioning. This vessel should close shortly after birth as the pressure in the pulmonary artery drops following perfusion of the lungs. Failure to close leads to a PDA. Blood flow through a PDA will be from the aorta too the pulmonary artery after birth (High to Low pressure)
What is a mechanical murmur?
A Mechanical Murmur is heard constantly throughout systole/diastole, as pressure in the aorta is always greater than in the pulmonary artery.
What is the clinical significance of left to right shunting?
Although left to right shunting of blood does not cause cyanosis it can be problematic later on if untreated, with the extent of the problems depending on the degree of shunting. Chronic left to right shunting can lead to vascular remodelling of the pulmonary circulation and an increase in pulmonary resistance. If the resistance of the pulmonary circulation increases beyond that of the systemic circulation the shunt will reverse direction as pressures on the right side of the heart increase (Eisenmenger Syndrome).
What is coarctation of the Aorta?
Coarctation of the Aorta is a narrowing of the aortic lumen in the region of the ligamemtum arteriosum (former ductus arteriosus). The narrowing of the aorta increases the afterload on the left ventricle and can lead to left ventricular hypertrophy.
Because the vessels to the head and upper limbs usually emerge proximal to the Coarctation, the blood supply to these regions is not compromised. However blood flow to the rest of the body is reduced. The extent of the symptoms depends on the severity of the Coarctation.
In very severe cases, an infant may present with symptoms of heart failure shortly after birth. In mild cases, the defect may be detected in adult life. Femoral pulses will be weak and delayed, with upper body hypertension.
What are the four components of tetralogy of fallot?
The four abnormalities are:
- VSD
- Overriding Aorta
- Pulmonary Stenosis (variable degree)
- Right Ventricular Hypertrophy (variable degree)
Pulmonary stenosis causes persistence of the foetal right ventricular hypertrophy, as the right ventricle must operate at a higher pressure to pump blood through the pulmonary artery. The increased pressure on the right side of the heart, along with the VSD and overriding aorta allow right to left shunting and therefore the mix of deoxygenated blood with the oxygenated blood going to the systemic circulation, resulting in cyanosis.
The magnitude of the shunt and level of severity depends on the severity of the pulmonary stenosis. Affected individuals may present with cyanosis in infancy, but mild cases can present in adulthood.
What is tricuspid atresia?
Tricuspid Atresia is the lack of development of the tricuspid valve. This leaves no inlet to the right ventricle. There must be a complete Right Left shunt of all blood returning to the right atrium (ASD or PFO) and a VSD or PDA to allow blood to flow to the lungs.
Describe the transposition of the great arteries
Results in two unconnected parallel circulations instead of two in series. In this defect, the right ventricle is connected to the aorta and the left ventricle to the pulmonary trunk. This condition is not compatible with life after birth, unless a shunt exists to allow the two circulations to communicate. A shunt must be maintained or created immediately following birth to sustain life until surgical correction can be made. The ductus arteriosus can be maintained patent and/or an atrial septal defect formed.
What is a hypoplastic left heart?
In some cases the left ventricle and ascending aorta fail to develop properly resulting in a condition called Hypoplastic left heart. A PFO or ASD are also present and blood supply to the systemic circulation is via a PDA. Without surgical correction this is lethal.
