In tetralogy of Fallot, which intraoperative strategy most effectively reduces the magnitude of the right-to-left intracardiac shunt?

In tetralogy of Fallot, which intraoperative strategy most effectively reduces the magnitude of the right-to-left intracardiac shunt?

• A. Increase systemic vascular resistance
• B. Increase pulmonary vascular resistance
• C. Decrease systemic vascular resistance
• D. Decrease pulmonary vascular resistance

Answer: (A)

The key idea is that the amount of right-to-left shunting in tetralogy of Fallot is driven by the relative pressures in the systemic and pulmonary circulations. When right ventricular outflow obstruction keeps RV pressure high, blood tends to cross the VSD into the left heart and then into the systemic circulation. To reduce this shunt, you want to make the left-sided pressure relatively higher than the right-sided pressure. Increasing systemic vascular resistance raises left ventricular afterload and systemic arterial pressure, pushing LV pressure higher and diminishing the driving force for blood to move right-to-left across the VSD. In practice, that’s achieved with vasopressors that elevate SVR (for example, phenylephrine), while avoiding anything that lowers SVR or raises pulmonary vascular resistance, both of which would worsen the shunt. Greater pulmonary vascular resistance would push more blood toward the right heart and the shunt, and lower SVR would make the LV pressure less dominant over the RV pressure, also increasing shunting.

The key idea is that the amount of right-to-left shunting in tetralogy of Fallot is driven by the relative pressures in the systemic and pulmonary circulations. When right ventricular outflow obstruction keeps RV pressure high, blood tends to cross the VSD into the left heart and then into the systemic circulation. To reduce this shunt, you want to make the left-sided pressure relatively higher than the right-sided pressure. Increasing systemic vascular resistance raises left ventricular afterload and systemic arterial pressure, pushing LV pressure higher and diminishing the driving force for blood to move right-to-left across the VSD. In practice, that’s achieved with vasopressors that elevate SVR (for example, phenylephrine), while avoiding anything that lowers SVR or raises pulmonary vascular resistance, both of which would worsen the shunt. Greater pulmonary vascular resistance would push more blood toward the right heart and the shunt, and lower SVR would make the LV pressure less dominant over the RV pressure, also increasing shunting.