The terms congenital and acquired are frequently used in medicine to describe a disorder, disease or defect that is either present from birth (congenital) or develops during the course of life (acquired). Congenital defects stem from fetal development but is often only obvious after birth once the baby’s body has to sustain life independent of the mother. However, with modern investigative techniques, many congenital disorders can be detected during fetal life and the appropriate measures taken prior to birth in certain cases. Congenital diseases or defects can affect any part of the body or organ and the heart and great blood vessels are no exception. These diseases and defects can be life-threatening and require intervention in fetal life or immediately after birth while in some cases it may only manifest later in life or adulthood.
What is congenital heart disease?
Congenital heart disease or defect is any type of structural abnormality of the heart and/or great blood vessels that arises in fetal life. It is a broad term to describe a number of abnormalities most of which occur during the formation of the heart and blood vessels around week 3 to 8 of fetal life. Congenital heart diseases and defects occur in about 1% of births (about 10 in 1,000 births) but in certain countries this may be as high as 50 in 1,000 births. These disorders are more frequently seen in preterm births and stillbirths.
A congenital defect may affect the heart’s ability to pump blood, disrupts the oxygenation of blood, allows blood to flow backwards and restrict the quantity of blood flowing out of the heart and into the vessels. The effects varies based on the type and severity of defect or disease. With minor defects, it is possible to remain asymptomatic for long periods of time or even throughout life. Some defects may only present with symptoms in childhood or even in adulthood. However, severe defects can affect fetal development, presents with a host of signs and symptoms from birth, and can lead to death of the fetus or newborn baby.
The Human Heart
The basic structure of the human heart is as follows :
- The heart has four chambers – two atria that receive blood and two ventricles that pump out blood.
- The right atrium and right ventricle are responsible for receiving deoxygenated (oxygen deficient) blood from the body via the vena cava and pushing it to the lungs for oxygenation.
- The left atrium and left ventricle are responsible for receiving newly oxygenated blood from the lungs and pushing it out to the rest of the body.
- Between the chambers and blood vessels lie several valves that prevent backward flow of blood.
- The septa is a thick wall that separates the right and left chambers of the heart and prevents the mixing of oxygen-deficient and oxygen-rich blood.
- The blood vessels that carry blood into and out of the heart are referred to as the great blood vessels.
- The wall of the heart is largely muscular (myocardium) and has its own blood supply (coronary arteries).
Congenital diseases and defects can affect the structure and function of any part of the heart and great blood vessels. It is mainly the septa, heart valves and heart muscle that are affected.
Fetal Heart Development
A background knowledge of cardiac formation in fetal life (embryology) is helpful in understanding how congenital defects arise. It is a complex process that starts around week 3 of fetal life at approximately day 15. In the early stages, the fetus is a ball of cells which organize into different layers of cells. One of these layers is known as the mesoderm, which is a middle layer lying between the inner endoderm and outer ectoderm layers. The cells that develop into the heart and great blood vessels are from the peripheral lateral mesoderm which move to the midline in waves.
This creates a crescent of cells which make up the first and second heart fields. By day 20 the cells start to organize to form a beating tube and by day 28 the basic structure of the heart chambers and blood vessels develop. Most of the first heart field forms the left ventricle while the second heart field forms the atria (left and right atrium) and right ventricle. By day 50, the septa that divides the atria and ventricles as well as the heart valves form and gives rise to the heart with its four distinct chambers.
Genetic and hormonal factors orchestrate the entire process. Movement of blood from even the earliest stage of fetal development may also play a role in shaping the formation of the heart and blood vessels. Structural defects associated with congenital heart disease primarily cause cardiac shunts or obstruction to blood flow.
Causes of Congenital Heart Disease
Most congenital heart defects arise due to genetic abnormalities but a disturbance of any other factor that plays a role in cardiac development may also be responsible. Environmental factors may also be responsible for congenital heart disease usually in combination with genetic factors.
Some of the causes and risks associated with congenital heart disease includes :
- Genetic abnormalities
- Rubella (German measles)
- Gestational diabetes
- Maternal systemic lupus erythematosus
- Medication used during pregnancy
- Alcohol and narcotic drug use during pregnancy
- Cigarette smoking during pregnancy
Nutritional deficiencies may also play a role in congenital heart defects and multivitamin supplements with folate may reduce this risk.
Signs and Symptoms
Congenital heart disease may present with signs and symptoms from birth or only become later in life even as late as in adulthood. The clinical features which may be present include :