So I have divided the post into two parts - A short summary for those who don't have the time to read everything (#TLDR) and a nice long explanation for those who want to read everything :)
Let's start with TLDR.
#TLDR: In TGA, oxygen-poor blood from the body enters the right side of the heart. But, instead of going to the lungs, the blood is pumped directly back out to the rest of the body through the aorta.
Oxygen-rich blood from the lungs entering the heart is pumped straight back to the lungs through the main pulmonary artery. Survival is impossible without shunts like VSD, ASD and PDA. (PGE1 to maintain PDA is treatment!)
Infants of diabetic mothers
It is more common in males
Cyanosis at birth, Parasternal heave, Loud S2
CXR - Egg-shaped heart, increased pulmonary blood flow
Echocardiography is diagnostic
Let's learn about the transposition of great arteries in detail...
So...What is-Transposition of the Great Arteries?
It is a birth defect of the heart in where the two main arteries carrying blood out of the heart – the pulmonary artery and the aorta – are switched in position, or “transposed.”
Physiologically the aorta is behind the pulmonary artery but here it is in front of it.... In addition to that..
Depending on the position of the aorta it is classified as
1) D(dextro)-tga : the aorta is to the right of the pulmonary artery.)
2)L(levo)-tga :the aorta is to the left of the pulmonary artery.( This is a rarer defect.)
In TGA, oxygen-poor blood from the body enters the right side of the heart. But, instead of going to the lungs, the blood is pumped directly back out to the rest of the body through the aorta.
Oxygen-rich blood from the lungs entering the heart is pumped straight back to the lungs through the main pulmonary artery.
So there are to independent circuits functioning here.
Survival is impossible without few other cardiac defects in the form of shunts.... like
1) Ventricular septal defect2
2)Arial septal defect
3)patent ductus arteriosus.
These shunts will allow mixing of the blood to help increase the oxygen saturation of the systemic circulation.
Infants of diabetic mothers and in males (3 : 1). d-TGA, especially when accompanied by other cardiac defects like pulmonic stenosis or right aortic arch, can be associated with deletion of chromosome 22q11.2 (DiGeorge syndrome).
CLINICAL MANIFESTATIONS :
This condition is a medical emergency,
Cyanosis and tachypnea recognized within the 1st hr or days of life.
Hypoxemia is usually moderate to severe.
Physical findings, other than cyanosis, may be remarkably nonspecific.
Parasternal heave may be present.
2nd heart sound is usually single and loud, although it may be split.
Murmurs may be absent, or a soft systolic ejection murmur may be noted at the midleft sternal border.
Electrocardiogram is usually normal, showing the expected neonatal right-sided dominant pattern.
Chest x-rays may show mild cardiomegaly, a narrow mediastinum (the classic “egg-shaped heart”), and normal to increased pulmonary blood flow. In the early newborn period, the chest x-ray is generally normal.
Echocardiography is diagnostic and confirmatory.
On suspection, an infusion of prostaglandin E1 is initiated immediately to maintain patency of the ductus arteriosus and improve oxygenation (dosage: 0.01-0.20 µg/kg/min).
Because of the risk of apnea associated with prostaglandin infusion, neonatal endotracheal intubation should be available.
Hypothermia intensifies the metabolic acidosis resulting from hypoxemia, and thus the patient should be kept warm.
Infants who remain severely hypoxic or acidotic despite prostaglandin infusion should undergo Rashkind balloon atrial septostomy. also usually performed in all patients in whom any significant delay in surgery is necessary.
Some patients with TGA and VSD may require balloon atrial septostomy because of poor mixing, even though the VSD is large.
Others may benefit from decompression of the left atrium to alleviate the symptoms of increased pulmonary blood flow and left-sided heart failure.
The arterial switch (Jatene) procedure is the surgical treatment of choice for neonates with d-TGA and an intact ventricular septum and is usually performed within the 1st 2 wk of life.
The reason for this time frame is ... pulmonary vascular resistance declines after birth ,pressure in the left ventricle (connected to the pulmonary vascular bed) also declines.
This drop in pressure results in a decrease in left ventricular mass over the 1st few wk of life. If the arterial switch operation is attempted after left ventricular pressure (and mass) has declined too far, the left ventricle will be unable to generate adequate pressure to pump blood to the high pressure systemic circulation.
The arterial switch operation involves dividing the aorta and pulmonary artery just above the sinuses and reanastomosing them in their correct anatomic positions.
The coronary arteries are removed from the old aortic root along with a button of aortic wall and reimplanted in the old pulmonary root (the “neoaorta”).
By using a button of great vessel tissue, the surgeon avoids having to suture directly onto the coronary artery The procedure has a survival rate of >95% for uncomplicated d-TGA. It restores the normal physiologic relationships
Atrial switch procedures reverse blood flow at the atrial level by the creation of an interatrial baffle that directs systemic venous blood returning from the vena cavae to the left atrium, where it will enter the left ventricle and then, via the pulmonary artery, the lungs. The same baffle also permits oxygenated pulmonary venous blood to cross over to the right atrium, right ventricle, and aorta. It is not recommend as it has a lot of complications of rhythm also leaves the right ventricle as the pumping chamber and these “systemic” right ventricles often begin to fail in young adulthood.
Well that was extensive...🤓But I hope it wasn't boring!😌