Cardiac shunt

Cardiac shunt
Synonyms	N/A
Pronounce	N/A
Field	Cardiology
Symptoms	Varies by type and severity; may include cyanosis, fatigue, dyspnea, heart murmur
Complications	Heart failure, pulmonary hypertension, stroke
Onset	N/A
Duration	N/A
Types	N/A
Causes	Congenital heart defects, surgical or acquired defects
Risks	Congenital anomalies, heart surgery, trauma
Diagnosis	Echocardiography, cardiac catheterization, MRI, CT scan, oxygen saturation studies
Differential diagnosis	N/A
Prevention	N/A
Treatment	Observation, cardiac surgery, catheter-based intervention, prostaglandin therapy
Medication	N/A
Prognosis	Depends on size and type of shunt; some close spontaneously, others may lead to severe complications
Frequency	N/A
Deaths	N/A

Cardiac shunt refers to an abnormal pattern of blood flow in the heart that deviates from the normal circulation between the lungs and the body. It may be described based on the direction of blood flow, such as:

• Left-to-right shunt
• Right-to-left shunt
• Bidirectional shunt

It may also be described as:

• Systemic-to-pulmonary
• Pulmonary-to-systemic

The direction and magnitude of the shunt are influenced by pressure differences between the left and right sides of the heart, the presence of congenital or acquired defects, and may be controlled by natural or artificial heart valves.

Normal Circulation

In normal cardiac circulation, deoxygenated blood from the body enters the right atrium, flows into the right ventricle, and is pumped to the lungs via the pulmonary artery. Oxygenated blood returns from the lungs into the left atrium, then into the left ventricle, and is pumped to the body via the aorta.

Types of Cardiac Shunts

Left-to-Right Shunt

A left-to-right shunt occurs when oxygenated blood from the left heart re-enters the right heart and is sent back to the lungs. This occurs when pressure in the left heart is higher than the right, which is typical in mammals. Causes include:

• Atrial septal defect (ASD)
• Ventricular septal defect (VSD)
• Patent ductus arteriosus (PDA)
• Atrioventricular septal defect (AVSD)

Right-to-Left Shunt

A right-to-left shunt allows deoxygenated blood to bypass the lungs and enter the systemic circulation, leading to hypoxemia and cyanosis. Causes include:

• Tetralogy of Fallot
• Eisenmenger syndrome
• Severe pulmonary hypertension with reversal of a left-to-right shunt

Bidirectional Shunt

Bidirectional shunting occurs when blood flows both left-to-right and right-to-left across a defect, depending on fluctuating pressure gradients.

Congenital Cardiac Shunts

Shunts resulting from congenital heart defects are among the most common forms:

• ASD – May be asymptomatic or cause fatigue and recurrent respiratory infections.
• Patent foramen ovale (PFO) – Often asymptomatic but may be associated with cryptogenic stroke.
• VSD – Symptoms depend on the size of the defect; large VSDs may cause heart failure.
• PDA – May lead to pulmonary overcirculation and heart failure.

In complex defects such as d-Transposition of the great arteries (d-TGA), shunts may be necessary to preserve oxygenation.

Acquired Cardiac Shunts

Biological

Some shunts are therapeutically created or modified:

• Balloon septostomy – Performed to enlarge a PFO or ASD, often in newborns with d-TGA.
• Prostaglandin E1 therapy – Used to maintain ductal patency in neonates with ductus-dependent congenital defects.
• Surgical or traumatic shunts – May develop after cardiac surgery or chest trauma.

Diagnostic Evaluation

Cardiac shunts are evaluated by:

• Echocardiography – Including bubble study for PFO
• Cardiac MRI or CT angiography
• Cardiac catheterization with shunt run:
• Blood samples are collected from:
• Superior vena cava (SVC)
• Inferior vena cava (IVC)
• Right atrium and ventricle
• Pulmonary artery
• Systemic arterial circulation
• Abrupt increase in oxygen saturation at specific cardiac levels suggests a left-to-right shunt.
• Reduced systemic oxygen saturation suggests a right-to-left shunt.

Treatment

Treatment depends on the type, size, and clinical impact of the shunt:

• Observation for small, asymptomatic defects
• Percutaneous device closure for ASDs and PFOs
• Surgical repair for large VSDs, AVSDs, or associated structural defects
• Medical therapy for symptoms (e.g., diuretics, ACE inhibitors)
• Heart–lung transplant in severe, irreversible pulmonary vascular disease

Prognosis

The outcome of a cardiac shunt depends on:

• Size and direction of the shunt
• Presence of associated cardiac anomalies
• Timing and success of treatment
• Pulmonary vascular resistance

Small defects may close spontaneously, while large defects may cause progressive pulmonary hypertension and heart failure if not treated.

See Also

• Congenital heart disease
• Echocardiography
• Cardiac catheterization
• Pulmonary hypertension
• Cyanotic heart disease
• Septal defect
• Foramen ovale