Transposition of the Great Arteries (TGA), the second most common congenital cardiac defect appearing in early infancy, is caused due to abnormal development of the fetal heart during the first eight weeks of pregnancy. As a result of this abnormal development, the two major arteries, the aorta and pulmonary artery, are malpositioned or reversed. Thus, the aorta receives deoxygenated blood from the right ventricle and carries the same blood back into systemic circulation, without undergoing oxygenation. Similarly, the pulmonary arteries receive pure deoxygenated blood from the left ventricle, and carry it back into the lungs once again. Almost 90% of affected infants become cyanotic in the first day of life itself. Some may even show cyanosis within the first few hours. Cyanosis is more severe if other cardiac defects like patent ductus atreriosus are also present. Apart from cyanosis, other common symptoms of the condition include rapid and labored breathing, a rapid heart rate, lack of appetite, weight loss, and cold and clammy skin. About 5-7% of all congenital heart defects are TGA. Interestingly, the condition affects more boys than girls.
Chest X-rays, electrocardiograms, echocardiograms, and/or cardiac catheterization are used to diagnose this congenital defect in infants. Surgery is a must for effective management of the condition. Since the affected individuals are infants, initially, a temporary procedure connecting the two atria may be performed, in order to delay the actual surgical procedure. Surgery may be one of two kinds. The atrial or venous switch (also known as the Mustard or the Senning procedure), involves creating a tunnel between the atria to redirect the oxygenated blood to the right ventricle and the aorta, and the deoxygenated blood to the left ventricle and the pulmonary artery. The other procedure, known as the arterial switch procedure involves switching the two major arteries back to their correct position, connecting the aorta to the left ventricle, and the pulmonary artery to the right ventricle. Patients, however, need to be followed up their entire life for any complications, including decline in cardiac function, arrythmias, and/or endocarditis. Patients are recommended to be on medications for their entire life, and to limit their physical activity.
In a study to assess the epidemiology of congenital heart disease (CHD) at the American University of Beirut-Medical Center, Bitar et al. (1999) reviewed the medical records of all cardiac patients seen at the outpatient cardiology clinic (OPD) between 1980 and 1995. The frequency of CHD was reported among three groups: 1980-1995 OPD groups (Group A; 883 patients); the group with CHD seen during the year 1995 (Group B; 344 patients); and (Group C), a subgroup of group B, included all newborns with CHD born during the year 1995. The incidence of CHD was 11.5/1,000 live births. Bitar et al. (1999) observed a relatively low prevalence of complex lesions (i.e., hypoplastic left heart syndrome, transposition of the great arteries) and a relatively high prevalence of the simpler cardiac malformation (i.e., ventricular and atrial septal defects, pulmonary stenosis) in Groups A and B.
In 2006, Yunis et al. studied the independent effect of consanguinity on the prevalence of congenital heart defects (CHDs), in 173 newborns admitted to nine hospitals located in Beirut, Lebanon and members of the National Collaborative Perinatal Neonatal Network (NCPNN) during a 3-year period from January 1, 2000 to December 31, 2002. Controls consisted of a random sample of 865 newborns without a CHD admitted during the same period. First cousin consanguinity remained significantly associated with an increased risk of CHD: infants born to first cousin marriages had a 1.8 times higher risk of having a CHD diagnosed at birth compared to those born to unrelated parents (95% CI: 1.1-3.1). However, no association was found with d-transposition of the great arteries, coarctation, pulmonary atresia (PA), atrioventricular septal defect (AVSD), and tetralogy of Fallot (TOF).
Sawardekar (2005) conducted a study to establish the prevalence of major congenital malformations in children born during a 10-year period in Nizwa Hospital. Of the 21,988 total births in the hospital, three children were born with TGA.
Manzar et al. (2005) studied the head circumference of neonates with TGA, since the head circumference was directly related to fetal blood flow and brain volume. Data of all neonates born between 1996 and 2003 were reviewed with exclusion of those who were small for dates, had multi-organ congenital anomalies, microcephaly, or chromosomal disorders and syndromes. The anthropometric measures (length and weight) in addition to the head circumference (measured by a measuring tape) were also included in the study. Results were compared to a group of infants with Hypoplastic Left Heart Syndrome (HLHS). The diagnosis of transposition of great arteries was confirmed by echocardiographic studies. The control group was a group of 46 term appropriate for gestational age newborns who were admitted to hospital during the study period with the diagnosis of transient tachypnea of the newborn. During the study period of eight years, 7396 neonates were admitted, out of whom 639 (8.6%) were admitted with malformations of the cardiovascular system. A total of 236 infants were excluded as their ages were not appropriate for gestational age and few had no available data on their head circumference. Out of the remaining 403 term appropriate for gestational age infants, 46 had TGA. Males (71%) were found to outnumber females (29%). The mean head circumference of the patient group with TGA was 33.7 cm which was significantly lower than that of the control group (34.4 cm), but significantly larger than that of a group of patients with HLHS. Manzar et al. (2005) explained this as due to the fact that cerebral blood flow was obstructed by the hypoplastic aortic isthmus in HLHS, which was absent in TGA in which the blood supply was adequate for appropriate growth. As regarding the birth weight, infants with TGA were found to be significantly heavier (mean weights of 3.136 Kg) than babies with HLHS (2.858 Kg), respectively. The mortality rate among those with TGA (13%) was significantly less than that of the HLHS group (60%). Out of the 46 infants with TGA, 41 infants were operated on with balloon atrial septostomy and arterial switch, two were critically sick and died before intervention, and parents of three infants refused the surgical operation. This study showed that postnatal intervention did not change the neurodevelopmental outcome in those infants as the damage was done in utero, which gave rise to a new strategy of perinatal intervention.
Alshehri (2005) studied the pattern and classification of all major congenital anomalies in Asir region between the years 1997 and 2002. Of the total of 691 neonates born with anomalies, eight were diagnosed with transposition of great arteries. This constituted 7% of neonates with circulatory system anomalies.
A case of neonatal death was reported by Al-Naami and Al-Mesned (2008); the case was of baby diagnosed at 30 hrs of age with d-transposition of great arteries and intact ventricular septum, restrictive foramen ovale, and constrictive ductus arteriosus. The 1-day-old baby was tentatively diagnosed with cyanotic congenital heart disease. Echocardiographic evaluation revealed d-TGA-IVS with restrictive foramen ovale. After the child was stabilized, his clinical condition deteriorated, resulting in death.
Almawazini and AlGhamdi (2011) screened 2610 children from Albaha region with congenital heart disease (CHD). Of these, 11 patients (1.9%) were found to have TGA.
Hosani and Czeizel (2000) evaluated the pilot dataset (March-May, 1998) of the UAE National Congenital Abnormality Registry (NCAR). A total of 4,861 births were recorded in this study period, with a birth prevalence of total congenital anomalies being 30.3 per 1,000 births. Transposition of great vessels was identified in four neonates, resulting in an incidence rate of 0.82 per 1,000 births.