Right-to-left shunt
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A right-to-left shunt is a cardiac shunt which allows, or is designed to cause, blood to flow from the right heart to the left heart. This occurs when:
- there is an opening or passage between the atria, ventricles, and/or great vessels; and,
- right heart pressure is higher than left heart pressure and/or the shunt has a one-way valvular opening.
The most common cause of right-to-left shunt is the Tetralogy of Fallot, a congenital cardiac anomaly characterized by four co-existing heart defects. The four defects include:
- Pulmonary stenosis (narrowing of the pulmonary valve and outflow tract, obstructing blood flow from the right ventricle to the pulmonary artery)
- Ventricular septal defect (defect in the ventricular septum, which divides the left and right ventricles of the heart)
- Overriding aorta (aortic valve is enlarged and appears to arise from both the left and right ventricles instead of the left ventricle, as occurs in normal hearts)
- Right ventricular hypertrophy (thickening of the muscular walls of the right ventricle)
A right to left shunt frequently causes hypoxemia.
