Congenital Heart Diseases, Pathogenesis And Clinical Features In Full Detail
Congenital heart diseases or defects are abnormalities of the heart or the large ducts present at birth. It accounts for 20% to 30% of all congenital malformations and covers a wide range of malformations, ranging from severe anomalies to intrauterine or perinatal survival, to lesions that are very rare. Or do not produce any symptoms, some of them at all. Not visible during pregnancy.
Congenital heart disease affects about 1% of newborns (or about 40,000 children a year in the United States). These cases are more common in premature babies and stillbirths, with about a quarter of them having major heart defects. Defects that allow for live birth usually affect only one chamber or area of the heart. 12 units account for 85% of congenital heart defects.
Thanks to advances in surgery, the number of survivors of congenital heart disease has risen sharply, to more than 2 million in the United States alone. Although hemodynamic abnormalities can be corrected with surgery, a rebuilt heart cannot be completely normal, as congenital defects can cause myocardial hypertrophy and cardiac remodeling irreversible.
In addition, almost all heart surgeries have some degree of myocardial infarction. Such changes can be caused by arrhythmias and myocardial dysfunction, sometimes years after surgical correction.
Congenital heart disease is most often caused by a violation of the fetus during the 3 to 8 weeks of pregnancy, when vital cardiac structures are developing. In about 90% of cases, the cause is unknown. Of the generally recognized etiological factors, environmental factors, including congenital rubella, teratogenesis and maternal diabetes, as well as genetic factors, are the most prominent.
Genetic factors include familial congenital heart disease and certain chromosomal abnormalities in some chromosomal abnormalities (e.g., trisomy 13, 15, 18, and 21 and Turner syndrome).
Cardiac morphogenesis involves several genes that work together to form a complex series of strictly controlled events. Key phases include the attachment of progenitor cells to myocardial projectors, the formation and looping of cardiac tubes, the division and expansion of cardiac chambers, the formation of cardiac valves, and the connection of large arteries to the heart.
This significant change depends on the network of transcription factors and different pathways and signaling molecules, including Wnt, vascular endothelial growth factor (VEGF), bone morphogenetic protein (BMP), transforming growth factor-β (TGF-β), and the way of the sign. Also important for cardiac morphogenesis is the mechanical force that accelerates blood flow, which is felt through the heart cells and the developing arteries.
Because the construction of a normal heart involves many steps, even the smallest obstacles can adversely affect the results. The most common genetic disorder is an autoimmune mutation that causes damage (or sometimes gain) to certain factors. Some variations include duplication factors. For example, atrial septal defect (ASD) and ventricular septal defect (VSD) and / or transmission defects may be caused by transcription factor mutations such as TBX5 mutations in Holt Orum syndrome.
Other disorders (e.g., Nunan syndrome) are associated with mutations in intracellular signaling cascades that lead to structural activation. Along with microRNA, epigenetic mutations (such as DNA methylation) are increasingly recognized as important factors.
Temporary environmental stress during the critical stages of early pregnancy can cause subtle changes in transcription factor activity that can reverse defects caused by hereditary mutations.
Different structural abnormalities in congenital heart defects can be divided into three main groups based on their clinical and hemodynamic findings:
- Malformations that cause left to right shunt
- Malformations that causes shunt from right to left (cyanotic congenital heart disease)
- Malformations that cause obstruction
A shunt is an abnormal communication between chambers or blood vessels. Depending on the pressure ratio, shunt allows blood to flow from left to right (or vice versa) of the heart.
- When blood is separated from right to left, the skin becomes dark blue (cyanosis) due to obstruction of pulmonary circulation and the oxygen deficient blood that accumulates in the venous system enters the circulation of systemic arteries.
- In contrast, shunting from left to right increases blood flow to the pulmonary circulation and is not (at least initially) associated with cyanosis. However, they revealed low pressure pulmonary circulation, low resistance to high pressure, and an increase in volume. These changes lead to adaptive changes that increase pulmonary vascular resistance to protect the pulmonary bed, resulting in right ventricular hypertrophy and ultimately right ventricular failure. Over time, an increase in pulmonary resistance can lead to shunt reversal (right to left) and late cyanosis.
- Some congenital defects prevent blood flow due to emptying of spaces, valves or large blood vessels. A defect characterized by complete obstruction is called atresia. In some diseases (e.g., pelvic tetralogy), obstruction (pulmonary artery stenosis) is also associated with anemia (right to left, via VSD).
Altered hemodynamics in congenital heart disease is often the result of spatial or wall hypertrophy. However, some defects result in a decrease in muscle mass or space size. This is called hypoplasia if it occurs before birth and if it occurs after birth.