Transposition of the Great Arteries (TGA)

• Mixed disorders involve a combination of increased pulmonary blood flow with obstruction to systemic blood flow.
• They encompass conditions like transposition of the great arteries (TGA), hypoplastic left heart syndrome (HLHS), truncus arteriosus, and others.

Transposition of the Great Arteries (TGA)

• TGA is a congenital heart defect where the aorta arises from the right ventricle and the pulmonary artery from the left ventricle.
• This results in systemic and pulmonary circulations that are parallel rather than in series.
• Deoxygenated blood returns to the right atrium and is pumped out through the aorta back to the body.
• Oxygenated blood returns to the left atrium and is pumped out through the pulmonary artery back to the lungs.
• Survival requires mixing of the two circulations.
• Mixing typically occurs through an atrial septal defect (ASD), ventricular septal defect (VSD), or patent ductus arteriosus (PDA).
• Cyanosis is present from birth due to the circulation of deoxygenated blood.
• Diagnosis is typically made shortly after birth based on cyanosis and confirmed by echocardiography.
• Treatment involves prostaglandin E1 infusion to maintain PDA patency, followed by surgical correction.
• The arterial switch operation is the preferred surgical approach.
• The arterial switch involves transecting the aorta and pulmonary artery, switching their positions, and re-implanting the coronary arteries.
• Without surgical intervention, TGA is fatal.

Hypoplastic Left Heart Syndrome (HLHS)

• HLHS is a severe congenital heart defect characterized by underdevelopment of the left ventricle, aorta, and mitral valve.
• The aorta is usually hypoplastic or atretic.
• Systemic blood flow is dependent on the PDA.
• After birth, as the ductus arteriosus closes, systemic perfusion decreases, leading to shock and death.
• Cyanosis is present, though it may be mild initially due to the mixing of blood.
• Diagnosis is made by echocardiography.
• Treatment options include staged surgical reconstruction, heart transplantation, or comfort care.
• Staged reconstruction involves the Norwood procedure, Glenn shunt, and Fontan procedure.
• The Norwood procedure creates a new aorta using the proximal pulmonary artery and places a shunt to provide pulmonary blood flow.
• The Glenn shunt connects the superior vena cava to the pulmonary artery.
• The Fontan procedure directs the inferior vena cava blood flow to the pulmonary artery.
• HLHS has a high mortality rate without intervention.
• Prostaglandin E1 is administered to maintain PDA patency until surgical intervention.

Truncus Arteriosus

• Truncus arteriosus is a rare congenital heart defect where a single arterial trunk arises from the heart, supplying the systemic, pulmonary, and coronary circulations.
• A VSD is usually present.
• Pulmonary blood flow is increased due to direct communication with the single arterial trunk.
• Cyanosis is variable, depending on the amount of pulmonary blood flow.
• Heart failure can develop due to volume overload.
• Diagnosis is made by echocardiography.
• Surgical repair involves separating the pulmonary arteries from the truncus arteriosus and creating a conduit from the right ventricle to the pulmonary arteries.
• The VSD is closed.
• The arterial trunk then functions as the aorta.
• Early surgical intervention is essential for survival.