Overview
Congenital heart diseases (CHD) describe defects in the structure of the heart or great vessels (aorta, pulmonary artery, pulmonary veins, inferior vena cava, and superior vena cava) that are present at birth.
Most defects obstruct the flow of blood in the heart or vessels near it or cause blood to take an abnormal route through the heart. CHD can be categorised into acyanotic causes and cyanotic causes.
Cyanotic Congenital Heart Defects
Overview
Cyanotic CHDs occur due to deoxygenated blood bypassing the lungs and entering the systemic circulation, or oxygenated and deoxygenated blood entering the systemic circulation.
They occur due to:
- Right-to-left shunting of the blood:
- Allows blood flow from the right heart to the left heart)
- Incorrect positioning of the great arteries (pulmonary artery and the aorta)
- The right heart pressure is higher than the left heart pressure (Eisenmenger syndrome)
Causes
Some conditions causing cyanosis at birth can include:
- Tetralogy of Fallot:
- Four congenital (a tetralogy of) cardiac defects: pulmonary stenosis, ventricular septal defect, right ventricular hypertrophy, and an overriding aorta
- Transposition of the great arteries:
- When the aorta leaves the right ventricle and the pulmonary artery leaves the left ventricle (they are swapped)
- Tricuspid atresia:
- Complete absence of the tricuspid valve and no connection between the right atrium and ventricle leading to a hypoplastic (undersized)/absent right ventricle
- Ebstein’s anomaly:
- When the tricuspid valve is at a lower position towards the apex of the right ventricle resulting in a large atrium and small ventricle
Eisenmenger syndrome
Left-to-right shunts are not usually cyanotic from the start but can become cyanotic over time. Due to increased blood entering the pulmonary circulation from the left-to-right shunt, there is pulmonary hypertension. The right ventricle hypertrophies (enlarges) to compensate for this pulmonary hypertension.
Eventually, the right ventricle generates a higher pressure than the left ventricle, and blood starts to flow from right to left, forming a right-to-left shunt. This leads to decreased deoxygenated blood getting to the lungs and it instead enters the systemic circulation leading to cyanosis.
Eisenmenger syndrome can occur in:
- Ventricular septal defects
- Atrial septal defects
- Patent ductus arteriosus
Acyanotic Congenital Heart Defects
Acyanotic CHDs describe left-to-right shunting of the blood and often occur due to holes in the interventricular septum. Describing these defects as ‘acyanotic’ is technically untrue, as over time, they can become cyanotic as described in Eisenmenger Syndrome.
Some acyanotic conditions include:
- Ventricular septal defects (VSD):
- Atrial septal defects (ASD):
- Patent ductus arteriosus (PDA):
- Aortic stenosis
- Pulmonary stenosis
- Coarctation of the aorta
