Tetralogy of Fallot involves what type of shunt?

Tetralogy of Fallot involves what type of shunt?

• A. Left-to-right shunt
• B. Right-to-left shunt
• C. Bidirectional shunt
• D. No shunt

Answer: (B)

Tetralogy of Fallot causes a right-to-left shunt due to obstruction of the right ventricular outflow tract. The pulmonary outflow obstruction raises right ventricular pressure above left ventricular pressure, so deoxygenated blood from the right ventricle flows through the VSD into the left ventricle and then into the systemic circulation via the aorta. This mixing of desaturated blood leads to cyanosis and hypoxemic spells. While pressures can vary and a bidirectional pattern can occur briefly in some moments, the characteristic and most clinically relevant shunt in TOF is right-to-left. Left-to-right would require higher left-sided pressures or increased pulmonary blood flow, which doesn’t occur here, and there is a shunt across the VSD with the outflow obstruction, so no shunt is not correct.

Tetralogy of Fallot causes a right-to-left shunt due to obstruction of the right ventricular outflow tract. The pulmonary outflow obstruction raises right ventricular pressure above left ventricular pressure, so deoxygenated blood from the right ventricle flows through the VSD into the left ventricle and then into the systemic circulation via the aorta. This mixing of desaturated blood leads to cyanosis and hypoxemic spells. While pressures can vary and a bidirectional pattern can occur briefly in some moments, the characteristic and most clinically relevant shunt in TOF is right-to-left. Left-to-right would require higher left-sided pressures or increased pulmonary blood flow, which doesn’t occur here, and there is a shunt across the VSD with the outflow obstruction, so no shunt is not correct.