A Review of Tetralogy Of Fallot

Most neonatal and prenatal mortalities are caused by congenital disorders. Congenital disorders are defects that affect certain body parts of infants and they are identifiable at birth. Congenital malfunctions are caused by an abnormality in ontogenetic development of a fetus. Congenital disorders are mostly induced by either genetic or environmental factors (Corsello and Giuffre, 2012). According to Corsello and Giuffre, congenital prevalence rate ranges between 2-3%. There exist various types of congenital malfunctions. They include congenital heart disorders, cleft palate and lip, Fetal Alcohol Syndrome (FAS), cerebral palsy among other disorders. Congenital heart disorder is one of the common types of congenital disorders.

Congenital heart disorders (CHD) are the most common types of congenital defects as well the commonest heart defects among infants. The heart defects in infants mostly arise from an abnormal development of a fetus or failure of an embryo to develop beyond the early embryonic development stage or early fetus stage (Setty, Patil, Ramegowda, Vijaykumar, Vijayalakshmi, Vijayalakshmi, Manjunath, 2017). According to Setty et al, CHD is defined as an abnormality in the structure of the heart or the intrathoracic great vessels.

Causes of Congenital Heart Defects

There are no known causes of most congenital heart defects. According to studies, known causes of CHD such as genetic syndromes and teratogens account for only 20% of CHD related cases. There is, however, a general acceptance that all CHD cases with unknown causes are caused by multifactorial causes made up of both environmental and genetic factors (Blue, Winlaw, Sholler, 2012). Studies, however, show that there are some known causes of congenital heart defects; they include genetic and environmental causes. Genetic causes include inherited chromosomal abnormalities, genetic point mutations, point deletions and other genetic abnormalities, syndromes such as Alagille syndrome and Noonan syndrome among others (Setty et al., 2017). Environmental factors include maternal infections, drugs and alcohol abuse, maternal illness such as diabetes mellitus, phenylketonuria, and systemic lupus erythematosus and high levels of stress (Setty et al., 2017).

Prevalence of Congenital Heart Disorders

Congenital heart defection is the most common congenital disease with studies showing that it represents 28% of all congenital diseases. Studies also show that congenital heart disease is the most common cause of deaths in infants across the world. Studies have also shown that out of a thousand live births, at least six to eight babies are affected by congenital heart diseases (Blue et al., 2012). It is also important to note that congenital heart defects are responsible for the higher rates of stillbirths, spontaneous abortions, and prematurity. Despite the higher prevalence, recent advancements in the diagnosis and surgical treatment of congenital heart defects, there has been a significant increase in the number of children who survive serious heart defects (Setty et al., 2017).

Congenital disorders are classified into two main classifications namely acyanotic and cyanotic. The classification depends on whether the patient exhibits cyanosis (Rao, 2009). Cyanotic congenital heart defects are however the common types of CHD.

In cyanotic congenital heart defects, systemic venous blood avoids passing pulmonary circulation but rather gets shunted across into the heart's left side thus causing systematic arterial desaturation. Cyanotic CHD does not include cyanosis because of the intrapulmonary right-to-left shunting and pulmonary venous desaturation secondary to congestive heart failure (Rao, 2009).

Cyanotic congenital heart defects are comprised of 5 types namely; Tetralogy of Fallot, transposition of the great arteries, tricuspid atresia, total anomalous pulmonary venous connection, and truncus arteriosus. However, the most common cyanotic defects include tetralogy of Fallot, transposition of the great arteries and tricuspid atresia (Rao, 2009).

Tetralogy of Fallot (TOF)

Studies show that 10% of all congenital heart defects are comprised of tetralogy Fallot which is a cyanosis occurring in infants aged beyond one-year-old. Tetralogy of Fallot is made up of a constellation of four abnormalities namely, ventricular septal defect (VSD), pulmonary stenosis (PS), right ventricular hypertrophy, and dextroposition of the aorta (Rao, 2009). The ventricular defect is large and often non-restrictive whereas the pulmonary stenosis shows a varying severity and nature of obstruction. On the other hand, the right ventricular hypertrophy mildly obstructs outflows thus leading to the initial left-to-right shunt at ventricular level. It should, however, be noted that severe right ventricular hypertrophy may cause severe cyanosis during the neonatal period. Dextroposition of the aorta which is also over-riding of aorta over the ventricular septum is a variable phenomenon. This is because the aorta's developmental anomaly is responsible for its largeness and not the physiologic abnormality of the TOF. It is important to note that 25% of TOF cases present the presence of right aortic arch (Rao, 2009).

Symptoms of Tetralogy of Fallot

The clinical presentation of Tetralogy of Fallot is depended on the degree of PS. If there are mild PS degrees, symptoms may not be present at infancy, they will appear during early childhood. If PS degrees are severe, the symptoms will appear at infancy. Tetralogy of Fallot symptoms includes an infant appearing pink as a neonate and developing cyanosis between 2 to 6 months of age. Symptoms also appear in the form of asymptomatic murmur, bluish color, hypercyanotic spells, and decreased tolerance of exercises (Rao, 2009).

Treatment and Management of Tetralogy of Fallot

Tetralogy of Fallot can be treated through surgical correction. Precautions should, however, be taken to avoid mortalities and morbidities as well as preventing complications related to TOF and other cyanotic heart defects. The surgical procedures should, however, be performed before the development of polycythemia (Rao, 2009). Exercises such as placing an infant with cyanotic spell on a knee-chest position have also been credited to be effective in managing TOF.

Transposition of the Great Arteries

Transposition of the great arteries (TGA) mostly presents during the newborn period. It is the most common cyanotic congenital heart defect. Studies show that 5% of all CHD and 10% of all neonatal cyanotic CHD are made up of Transposition of the great arteries (TGA). TGA is commonly defined as a condition where the aorta and the pulmonary artery rise from the morphologic right ventricle and the morphologic left ventricle respectively (Rao, 2009)

Symptoms of Transposition of the Great Arteries

TGA symptoms depend on its anatomic type that is whether it is Group I which is TGA with an intact ventricular septum, Group II which is made up of TGA with VSD or Group III which TGA with VSD and PS. Under group I, the infant presents cyanosis within the initial week of life or even within hours after birth. Sometimes infants may be asymptomatic but they become tachypnoeic and develop respiratory distress. In cases of lack of appropriate treatment, the patient becomes acidotic as well as lethargic, lacking spontaneous movement, and eventually die. Under group II, infants aged between 4-8 weeks present symptoms such as tachypnea, tachycardia, sweating, and poor feeding. Lastly, under group III, patients present various symptoms depending on the severity of the PS. In case of severe PS, patients present symptoms similar to those of TOF. But if the PS is moderate, the TGA symptoms appear late with long survival chances. In the case of mild PS, the patient exhibits signs of congestive heart failure and symptoms similar to those of group II (Rao, 2009).

Treatment of TGA

The management of TGA is similar to other cyanotic neonates. While managing a neonate with TGA, it is important to monitor the infant's temperature and maintain a neutral thermal environment. if the infant is hypoxemic, administration of ambient oxygen is recommended. TGA will be managed using several other interventions depending on the anatomic group or type of TGA. For instance, TGA patients with VSD require relieving the pulmonary venous congestion and improving oxygenation using balloon atrial septostomy. On the other hand, balloon atrial septostomy can be used to treat TGA patients with VSD and PS presenting hypoxemia as a result of poor mixing. Similar to TOF, TGA can also be treated using correctional surgery. For instance, a correctional surgery known as 'Jatene' that involves arterial switch is the most preferred surgical procedure in the treating hypoxemic infants (Rao, 2009).

Tricuspid Atresia (TA)

Tricuspid atresia is also another common congenital heart defect. It is described as the absence of the morphologic tricuspid valve at birth. Tricuspid atresia causes cyanosis with left ventricular hypertrophy. According to studies, 1.4% of all CHD are as a result of Tricuspid atresia. There are different types of Tricuspid atresia but the most common one is the muscular variety (Rao, 2009).

Symptoms of Tricuspid Atresia

A half of TA patients will present symptoms during the first day of birth while 80% of the patients will show TA symptoms by the end of the first month after birth. TA presents two modes of presentation depending on the timing and the magnitude of blood flow they include decreased pulmonary blood flow and increased pulmonary blood flow. Symptoms of cyanosis are present in patients with pulmonary oligemia. If there is decreased pulmonary blood flow, the infants may have hyperpnea and acidosis. On the other hand, infants who have pulmonary plethora present signs of heart failure within the first week or first day of life. Despite being less cyanotic, these patients present symptoms of dyspnea, fatigue, difficulty to feed, and perspiration (Rao, 2009)

Treatment of Tricuspid Atresia

Tricuspid atresia can be treated using corrective surgery known as Fontan-Kreutzer procedure. The procedure is however performed on patients older than two years. Therefore, TA patients should be managed well until they reach the required age of the corrective operation. Medical management of TA neonates includes maintaining a neutral thermal environment, maintaining a normal acid-base status, and ensuring appropriate normoglycemia and normocalcemia by appropriate monitoring and correction among other measures (Rao, 2009).

Present Day Research

In spite of improvements made in the treatment and management of most CHDs, there is still a niche in determining the causes of most CHDs. From the psychosocial perspective, it is important to determine the causes so as to be able to answer the 'why' and 'how' questions arising from patients and families. Knowledge of the etiology of CHD is also useful in family planning especially for both the parents and the affected child especially when he or she approaches reproductive age. Knowing the causes will also become handy during the clinical management of the patient. Possessing such knowledge will be helpful in identifying possible complications and risk factors attributable to surgery or treatment. Therefore there is a need for further research in identifying the causative factors of the majority of CHDs whose causes are still unknown. However, studies show that advances have been made in genetic technology that has updated the existing understanding of the causes of CHDs. Such advances include the use of novel genetic techniques like whole exome and genome sequencing to accelerate gene discovery and aid in identifying previously unknown causes of various diseases such as CHD (Blue et al., 2012).

Conclusion

Congenital disorders which are defects affecting an infant's certain body parts are responsible for most infant and neonatal fatalities. Most congenital malfunctions are caused by an abnormality in ontogenetic development of a fetus. According to studies, most congenital disorders are caused by multifactorial factors which can be either genetic or environmental. There exist various types of congenital diseases. Studies have however shown that congenital heart disorder is the most common type of congenital disorders. Studies also show that out of a thousand live births, six to eight infants are affected by congenital heart diseases. Congenital heart diseases can be classified into two main classifications namely acyanotic and cyanotic. Cyanotic congenital heart defects are however the common types of CHD. CHD patients present various symptoms but heart failure is the common symptom of most CHDs. Various CHDs can, however, be treated through correctional operations or surgeries.

References

Blue, G. M., Kirk, E. P., Sholler, G. F., Harvey, R. P., & Winlaw, D. S. (2012). Congenital heart disease: current knowledge about causes and inheritance. The Medical Journal of Australia, 197(3), 155-159. doi:10.5694/mja12.10811

Corsello, G., & Giuffrè, M. (2012). Congenital malformations. The Journal of Maternal-Fetal & Neonatal Medicine, 25(sup1), 25-29. doi:10.3109/14767058.2012.664943

Natraj Setty, H. S., Gouda Patil, S. S., Ramegowda, R. T., V, V., & Vijayalakshmi, I. B. (2017). Comprehensive Approach to Congenital Heart Defects. Journal of Cardiovascular Disease Research, 8(1), 01-05. doi:10.5530/jcdr.2017.1.1

Rao, P. S. (2009). Diagnosis and management of cyanotic congenital heart disease: Part I. The Indian Journal of Pediatrics, 76(1), 57-70. doi:10.1007/s12098-009-0030-4