Which would be the major characteristic of a cardiac malformation associated with left-to-right shunting?

• A. Increased blood flow to the lungs
• B. Increased hematocrit
• C. Severe growth delay
• D. Clubbing of the fingers and toes

Answer: (A)

Left-to-right shunting means oxygen-rich blood from the left heart flows back into the right heart and into the lungs, so the defining feature is increased pulmonary blood flow. This elevated flow to the lungs is the major characteristic of this type of cardiac malformation.

Increased hematocrit reflects polycythemia from chronic low oxygen levels typical of right-to-left shunts, not left-to-right. Severe growth delay isn’t a primary hallmark of left-to-right shunts, and clubbing of fingers and toes arises from chronic hypoxemia seen with cyanotic conditions (which can develop if such shunts progress to Eisenmenger physiology, but isn’t the initial characteristic).