Congenital Heart Defects
Congenital Heart Defects
Congenital heart defects represent abnormal development in the womb. They are the incorrect arrangement of certain sections of the heart or its blood vessels. The heart can have a single defect or a number of defects at once. Congenital heart defects are among the most common developmental defects. Development of the heart is a complicated process and discrepancies can appear at any stage of development. The crucial period for the heart's development is between the 2nd and 8th week of intrauterine development. Genetic and external factors can influence heart defects. Congenital heart defects of varying severity occur in approximately 1% of live births. They can manifest as a heart murmur, dyspnea, bluing of the child and heart failure. These symptoms often appear very soon after birth, though they can appear later in life, even in adulthood.
Causes of Congenital Heart defects
As mentioned above, congenital heart defects can develop as a result of genetic mistakes or external influences.
Genetic Causes of Congenital Heart Defects
The most frequent genetic cause is chromosomal aberration, where there is a structural or numerical discrepancy in the genetic material of an individual, which is reflected in different syndromes, including congenital heart defects. Some hereditary heart defects are the result of an error in only one gene, known as monogenic. Often, however, a combination of genetic errors and external influences are the cause, known as multifactorial developmental defects.
External Causes of Congenital Heart Defects
External factors that can cause changes in the genetic material are known as teratogens. If a woman is exposed to certain teratogens during pregnancy, there is no reason to panic as teratogens are only risky during certain fazes of pregnancy. It is, however, important to inform ones doctor who can determine if the fetus was put at risk and suggest next steps. Teratogens can be of a chemical, biological or physical nature.
- Chemical teratogens include heavy metals and solvents, as well as medications such as cytostatic, certain antibiotics, antiepileptic medications, warfarin, steroid substances and vitamin A. Teratogens also include alcohol, fumes released from smoking, and drugs.
- Physical teratogens include various types of ionizing radiation. This primarily includes X-rays, gamma-rays and high temperatures.
- Biological teratogens include various viruses and bacteria. The fetus is in danger if the pregnant mother gets sick with rubella, influenza viruses, cytomegalovirus or the HIV virus. Teratogen bacteria includes syphilis, i.e. Treponema pallidum.
Classification and Symptoms of Congenital Heart Defects
Some minor congenital heart defects do not necessarily affect the individual, whereas as others are incompatible with life. The most basic classification of congenital heart defects is the heart defects with shunts, and those without. One of the most common types of congenital heart defects is congenital valve defects. It is important to mention that in a healthy heart, blood from the left half and blood from the right half of the heart do not mix.
Congenital Heart Defects with a Shunt
Congenital heart defects that cause shunts allow blood to flow through an opening, which is not present in a normal heart, flowing from either the left side of the heart into the right, or vice versa depending on which side has a higher blood pressure. The right-left shunts, where blood flows from the right half of the heart into the left, are more clinically evident. This is the result of an atrial septal defect. It causes deoxygenated blood to circulate the body, without having been oxygenated by the lungs. This is manifested by cyanosis, a condition where mucous membranes and the skin turn blue due to lack of oxygen. Cyanosis can be seen most clearly on the lips, which are normally a deep red. Some children may experience this condition to such an extent that they are known by the nick-name "blue baby". Left-right shunts can eventually cause such a significant strain on the heart and pulmonary circulation that the pressure ratio in the heart may change and result in cyanosis. Left-right shunts appear in ventricular septal defects.
Congenital Heart Defects without Shunts
Congenital heart defects without shunts do not result in the above mentioned mixing of blood. The most common defect is coarctation of the aorta, i.e. narrowing of the largest artery in the human body. Depending on the part of the aorta that is narrowed, preductal and postductal types can be distinguished. In the former type, the aorta and its branches are normally provided with oxygenated blood, but the ductus, which is only present in fetuses and should close spontaneously after birth, is supplied with deoxygenated blood, which subsequently flows through the lower half of the body. This is manifested by bluing of the lower half of the body. This defect is incompatible with life and therefore requires immediate surgery. The second type is with the opening of the ductus, causing a left-right shunt, resulting in oxygenated blood to flow into the lungs, which are then overloaded and strained. In the event that the ductus is closed, manifestations appear in adulthood with hypertrophy of the left ventricle and a higher blood pressure in the upper half of the body than in the lower half.
Congenital Valve Defects
Valves are projections of the endocardium, a membrane lining the heart from the inside. They are units that work as valves, meaning they prevent backflow of blood. Correct function of the valves rests in their coordinated opening and closing in sync with contractions of the heart. If this does not occur, it as an indication of a valve defect. Congenital valve defects are among the most common congenital heart defects, and affect the aortic and pulmonary valves the most. The aortic valve lies between the left ventricle and the aorta, and the pulmonary valve lies between the right ventricle and the pulmonary artery. Congenital valve defects include valves that are narrowed, completely closed or immobile. Incorrect number of cusps is also a common defect, usually of the bicuspid aortic valve. Congenital valve defects typically manifest as a heart murmur, dyspnea (shortness of breath), swelling of the lower limbs, fatigue, chest pain and loss of consciousness. An electrocardiogram (EKG) is used for diagnosis of valve defects. The only treatment option is surgery.
Diagnosing Congenital Heart Defects
A diagnosis of congenital heart defects after birth is based on the above mentioned symptoms. Nowadays, the goal is to detect congenital heart defects before birth, i.e. with prenatal diagnosis. Prenatal diagnosis is significant in that with the detection of certain defects, care of the mother during pregnancy, and of the baby after birth can be planned. In the event that the defect in incompatible with life, the termination of pregnancy due to genetic causes is possible depending on the respective country's or state's abortion laws. Prenatal diagnosis of congenital heart defects can be invasive or noninvasive.
Invasive Prenatal Diagnosis
Invasive diagnosis is where a device penetrates into the body. It is performed under the suspicion of a specific defect, including developmental heart defects. All invasive methods are considered riskier that noninvasive as there is the possibility of loss of the fetus, occurring in 0.5-1% of cases. Amniocentesis, sampling of the chorionic villus and cordocentesis are among the most common invasive methods.
- Amniocentesis is a diagnostic procedure performed outpatient. It includes the piercing of the amniotic cavity where the fetus is situated and sampling of the amniotic fluid. The whole procedure is performed under ultrasound monitoring. Amniotic fluid undergoes genetic and biochemical examination where the presence of congenital heart defects or defects of other organs can be determined.
- Chorionic villus sampling (CVS) is a method where a needle is introduced, usually through the stomach of the pregnant woman, and a sample of the chorionic villus is taken. The whole procedure is performed under the visual monitoring of an ultrasound. The sample is sent for genetic testing. The advantage of this method is being able to perform it between the 10th and 13th week of gestation, sooner that the amniocentesis, allowing sooner detection of congenital defects.
- Cordocentesis is the piecing of the umbilical cord and sampling of the fetal blood under ultrasonic monitoring. The blood is sent for genetic testing, where heart and immune defects on the fetus, its blood type or any infections can be determined.
Noninvasive Prenatal Diagnosis
Noninvasive means that no device or foreign objects penetrate the body. In principle, these are methods that do not put the fetus or the mother at risk and are performed during regular screening. Screening is the "search" for individuals that are sick or at risk, where the presence of a certain illness or condition is expected, though no clinical manifestations have appeared. A blood test from the mother is performed first, followed by ultrasonic examination of the pregnant woman in the first trimester. The ultrasound can be used later as well, when a developmental heart defects is suspected.
Treatment of Congenital Heart Defects
Treatment of congenital heart defects usually requires surgery. The goal of the operation is to ensure correction of the defect as soon as possible after birth. Immediate correction is not possible with some defects, requiring palliative procedures, i.e. such that ensure survival, followed by definitive correction later, usually in adulthood. Some shunts may spontaneously close on their own. Heart surgery is performed by a doctor specializing in cardiac surgery. Today, in developed countries with good healthcare, about 85% of children with congenital heart defects reach adulthood, which compared with the prognosis of these children in the past decade or countries with lower-quality health care, is a huge achievement.