**Figure 3.**

*Anatomy of heart in LTGA.*

(PS) or atresia, overriding atrioventricular valves, coarctation of the aorta (COA), and aortic interruption [6–8]. The second most common defect in DTGA is left ventricular outflow tract obstruction (LVOO), detected in approximately 25% of the cases [9, 10]. LVOO may be anatomic or dynamic. If the interventricular septum is intact, the high pressure in RV, which may be at times equal to the systemic blood pressure, forces the ventricular septum to bulge into the LV cavity and thus creates a

**155**

*Transposition of Great Arteries*

30% and dextrocardia at <1%.

the sinus of Valsalva [12].

**5. Hemodynamics and pathophysiology**

*DOI: http://dx.doi.org/10.5772/intechopen.99205*

dynamic outflow obstruction. The dynamic obstruction is resolved when a conduit is formed between the two parallel circulations, either medically by reopening the DA with PGE1 or surgically by creating an atrial septal defect (ASD) by balloon septostomy. Other cardiac structural anomalies seen in DTGA involve atrioventricular

In LTGA the defect is congenitally corrected with atrioventricular discordance. Ventricles are inverted, and A arises from RV and PA from LV [7]. Despite transposition of the great arteries, deoxygenated blood is pumped into the lungs, while oxygenated blood circulates to the rest of the body. With this anomaly, therefore, a shunt is not needed. Anatomically, the aortic valve is anterior and to the left of the pulmonary valve. LTGA is associated more often with other cardiac anomalies, the common ones being VSD at 60–70%, PS at 30–50%, tricuspid regurgitation (TR) at

The coronary arteries are anatomically abnormal in about 33% of the patients with TGA [12]. The commonly reported anomalies are the left circumflex coronary originating from the right coronary artery in 22%, single right artery in 9.5%, single left coronary artery in 3%, or inverted coronary arteries in 3% of the cases. Their course towards their destination may be shortened and unusual, such as passing between the two great arteries. There may be multiple coronary ostia arising from

In DTGA, the deoxygenated blood coming from the superior and inferior vena cava normally drain into the right atrium (RA). From there, it passes over to the right ventricle (RV), then enters the systemic circulation via the abnormally connected Ao, and finally returns to the RA through the vena cava (**Figure 4**). The oxygenated blood in the pulmonary circuit enters the left ventricle (LV) via the left atrium (LA), is pumped into the abnormally connected pulmonary artery, and returns back to the LA via pulmonary veins. This circulatory pattern is incompatible with life and requires mandatory mixing between the two parallel circulations, which is achieved intracardiacally via the PFO, ASD or a VSD; or extracardiacally with a patent DA or

DTGA is well tolerated by the fetus as the intercirculatory mixing of blood is maintained by the open fosa ovalis and patent DA. Hemodynamically, during the. intrauterine life, the major part of the oxygen-rich blood coming from the umbilical vein enters the right atrium and passes across the fossa ovalis into the LV, from where it enters the pulmonary artery and eventually the systemic circulation via the open DA. The vascular resistance in the placental system is comparatively lower to that in pulmonary capillaries and thereby facilitates the right-to-left blood flow through the DA into the aorta. After birth, the volume of intercirculatory mixing decides the severity of hypoxemia, which is optimized by balancing the effective pulmonary and systemic blood flows [7, 8]. The effective systemic blood flow is defined as the volume of oxygenated pulmonary venous return reaching the systemic capillary bed, and the effective pulmonary blood flow, the systemic venous return entering the pulmonary capillary system via the intracardiac and extracardiac shunts. To be most efficient, the shunting of blood must be bidirectional, occurring during both systole and diastole. Being a lower pressure system, this happens better at the atrial level. The interventricular and extracardiac shunt flow may be unidirectional as they function in a high-pressure system across highpressure gradient. Keeping the shunt bidirectional and balanced is important, as a

other vascular channel of the bronchopulmonary collateral circulation.

preferential shunting to either side will lead to clinical deterioration.

valves, such as overriding valves or the straddling tricuspid valve [11].

#### *Transposition of Great Arteries DOI: http://dx.doi.org/10.5772/intechopen.99205*

*Congenital Anomalies in Newborn Infants - Clinical and Etiopathological Perspectives*

(PS) or atresia, overriding atrioventricular valves, coarctation of the aorta (COA), and aortic interruption [6–8]. The second most common defect in DTGA is left ventricular outflow tract obstruction (LVOO), detected in approximately 25% of the cases [9, 10]. LVOO may be anatomic or dynamic. If the interventricular septum is intact, the high pressure in RV, which may be at times equal to the systemic blood pressure, forces the ventricular septum to bulge into the LV cavity and thus creates a

**154**

**Figure 3.**

*Anatomy of heart in LTGA.*

**Figure 2.**

*Anatomy of heart in DTGA.*

dynamic outflow obstruction. The dynamic obstruction is resolved when a conduit is formed between the two parallel circulations, either medically by reopening the DA with PGE1 or surgically by creating an atrial septal defect (ASD) by balloon septostomy. Other cardiac structural anomalies seen in DTGA involve atrioventricular valves, such as overriding valves or the straddling tricuspid valve [11].

In LTGA the defect is congenitally corrected with atrioventricular discordance. Ventricles are inverted, and A arises from RV and PA from LV [7]. Despite transposition of the great arteries, deoxygenated blood is pumped into the lungs, while oxygenated blood circulates to the rest of the body. With this anomaly, therefore, a shunt is not needed. Anatomically, the aortic valve is anterior and to the left of the pulmonary valve. LTGA is associated more often with other cardiac anomalies, the common ones being VSD at 60–70%, PS at 30–50%, tricuspid regurgitation (TR) at 30% and dextrocardia at <1%.

The coronary arteries are anatomically abnormal in about 33% of the patients with TGA [12]. The commonly reported anomalies are the left circumflex coronary originating from the right coronary artery in 22%, single right artery in 9.5%, single left coronary artery in 3%, or inverted coronary arteries in 3% of the cases. Their course towards their destination may be shortened and unusual, such as passing between the two great arteries. There may be multiple coronary ostia arising from the sinus of Valsalva [12].
