8th March 2024

Pathophysiology

The degree of right ventricular outflow tract (RVOT) obstruction affects the severity of the disease. The VSD is typically large and unrestrictive, which means that the direction of blood flow across the VSD is dependent on the resistance to blood flow out of the right and left ventricular outflow tracts. As the degree of RVOT obstruction increases in TOF, the resistance to blood flow into the pulmonary circulation increases. If this pressure exceeds the systemic vascular resistance, it becomes easier for deoxygenated blood to flow from the RV into the LV across the large VSD, causing cyanosis. One of the pathophysiologic characteristics of TOF is a dynamic RVOT obstruction ranging from minimal obstruction to near-total occlusion, resulting in “tet spells’ (a short period when a child’s skin turns blue).