U01.07.031 Congenital heart diseases

Right-to-Left Shunts

Early Cyanosis: “Blue Babies”
Right-to-left shunts often lead to early cyanosis and are typically diagnosed prenatally or shortly after birth. These conditions usually require urgent surgical intervention or maintenance of a patent ductus arteriosus (PDA).

The 5 T’s of Right-to-Left Shunts:

Condition	Description
Truncus Arteriosus	One vessel instead of two, often with a VSD.
Transposition of the Great Vessels	Aorta arises from the right ventricle and pulmonary trunk from the left.
Tricuspid Atresia	Absence of the tricuspid valve, requiring both ASD and VSD for viability.
Tetralogy of Fallot	Characterized by four features: VSD, pulmonary stenosis, overriding aorta, and right ventricular hypertrophy.
TAPVR (Total Anomalous Pulmonary Venous Return)	Pulmonary veins drain into the right heart circulation.

Conditions and Pathophysiology

Persistent Truncus Arteriosus
- The aorticopulmonary septum fails to form, preventing the division of the pulmonary trunk and aorta. Most cases are accompanied by a VSD.
D-Transposition of the Great Vessels
- The aorta originates from the right ventricle and the pulmonary trunk from the left, leading to a separation of systemic and pulmonary circulations. This condition is incompatible with life unless a shunt (VSD, PDA, or patent foramen ovale) exists to mix blood.
- CXR Appearance: “Egg on a string” (due to the configuration of the vessels).
Tricuspid Atresia
- Absence of the tricuspid valve and hypoplastic right ventricle; viability requires both ASD and VSD.
Tetralogy of Fallot
- Caused by anterosuperior displacement of the infundibular septum.
- Key Features:
  - Pulmonary stenosis (most important for prognosis),
  - Right ventricular hypertrophy (RVH): “Boot-shaped heart” on CXR,
  - Overriding aorta and VSD,
  - Tet spells: Cyanotic episodes triggered by crying, fever, or exertion.
- Prognosis Improvement: Squatting increases systemic vascular resistance (SVR), improving the right-to-left shunt and cyanosis.
- Association: 22q11 syndromes.
TAPVR (Total Anomalous Pulmonary Venous Return)
- Pulmonary veins drain into the right heart (e.g., SVC, coronary sinus), often associated with ASD and sometimes PDA for right-to-left shunting, ensuring adequate cardiac output.
Ebstein Anomaly
- Displacement of the tricuspid valve leaflets downward into the right ventricle, causing “atrialization” of the ventricle. This condition is associated with tricuspid regurgitation, accessory conduction pathways, and right-sided heart failure.
- Possible Cause: Lithium exposure during pregnancy.

Left-to-Right Shunts

Initially Acyanotic; Cyanosis May Develop Later
These defects initially result in no cyanosis but may eventually cause late cyanosis. Common conditions include VSD, ASD, and PDA.

Ventricular Septal Defect (VSD)
- VSDs may be asymptomatic at birth but may manifest later. Larger defects can lead to left ventricular overload and heart failure.
- Oxygen Saturation: Decreased in the right ventricle and pulmonary artery.
Atrial Septal Defect (ASD)
- A defect in the interatrial septum leads to a wide, fixed split S2.
- Types:
  - Ostium Secundum (most common, usually isolated),
  - Ostium Primum (rarer, often associated with other cardiac anomalies).
- Symptoms vary from none to heart failure.
- Oxygen Saturation: Decreased in the right atrium, right ventricle, and pulmonary artery.
- Complications: Paradoxical emboli, especially in cases of systemic venous emboli using the ASD to bypass the lungs.
Patent Ductus Arteriosus (PDA)
- Normally right-to-left in fetal life; after birth, increased pulmonary vascular resistance leads to a left-to-right shunt, causing progressive right and/or left ventricular hypertrophy and heart failure.
- Characteristic Murmur: Continuous “machine-like” murmur.
- Clinical Outcome: If uncorrected, PDA can result in late cyanosis in the lower extremities (differential cyanosis).
Eisenmenger Syndrome
- An uncorrected left-to-right shunt (VSD, ASD, PDA) leads to increased pulmonary blood flow, causing pulmonary hypertension and eventually reversing the shunt to right-to-left.
- Clinical Manifestations: Late cyanosis, clubbing, and polycythemia.

Other Anomalies

Coarctation of the Aorta
- Aortic narrowing near the insertion of the ductus arteriosus (juxtaductal).
- Clinical Features: Hypertension in the upper extremities, weak and delayed pulse in the lower extremities (brachial-femoral delay).
- CXR: “Notched” appearance due to enlarged intercostal arteries.
- Associated Conditions: Bicuspid aortic valve, Turner syndrome, and other congenital heart defects.

Congenital Cardiac Defect Associations

Disorder	Associated Defects
Alcohol Exposure in Utero (Fetal Alcohol Syndrome)	VSD, PDA, ASD, Tetralogy of Fallot
Congenital Rubella	PDA, Pulmonary artery stenosis, Septal defects
Down Syndrome	AV septal defect, VSD, ASD
Infant of Diabetic Mother	Transposition of great vessels, VSD
Marfan Syndrome	MVP, Thoracic aortic aneurysm and dissection, Aortic regurgitation
Prenatal Lithium Exposure	Ebstein anomaly
Turner Syndrome	Bicuspid aortic valve, Coarctation of the aorta
Williams Syndrome	Supravalvular aortic stenosis
22q11 Syndromes	Truncus arteriosus, Tetralogy of Fallot

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