Accidental air injection into a peripheral vein is least likely to cause arterial air embolism in a patient with which congenital heart defect?

Accidental air injection into a peripheral vein is least likely to cause arterial air embolism in a patient with which congenital heart defect?

• A. Patent ductus arteriosus
• B. Eisenmenger's syndrome
• C. Tetralogy of Fallot
• D. Pulmonary atresia with ventricular septal defect

Answer: (A)

The key idea is that arterial air embolism from a venous injection happens when air can bypass the lungs and enter the arterial system, typically via a right‑to‑left shunt or abnormal mixing. In a patient with a patent ductus arteriosus, the usual situation is a left‑to‑right shunt, meaning blood goes from the aorta to the pulmonary arteries rather than from the venous side to the arterial side. If air is accidentally injected into a vein, it travels to the right heart and then to the lungs, where it is largely filtered or trapped, so the chance of the air reaching the arterial circulation is minimal. Therefore, this defect makes arterial air embolism least likely. In contrast, Eisenmenger’s syndrome involves reversal of the shunt to right‑to‑left due to high pulmonary pressures, allowing venous air to pass directly into the arterial system. Tetralogy of Fallot and pulmonary atresia with VSD both create scenarios where right‑to‑left mixing can occur, again permitting paradoxical or arterial embolization of air. So, the defect least likely to permit arterial air embolism from venous air is the patent ductus arteriosus, unless it has progressed to Eisenmenger physiology.

The key idea is that arterial air embolism from a venous injection happens when air can bypass the lungs and enter the arterial system, typically via a right‑to‑left shunt or abnormal mixing.

In a patient with a patent ductus arteriosus, the usual situation is a left‑to‑right shunt, meaning blood goes from the aorta to the pulmonary arteries rather than from the venous side to the arterial side. If air is accidentally injected into a vein, it travels to the right heart and then to the lungs, where it is largely filtered or trapped, so the chance of the air reaching the arterial circulation is minimal. Therefore, this defect makes arterial air embolism least likely.

In contrast, Eisenmenger’s syndrome involves reversal of the shunt to right‑to‑left due to high pulmonary pressures, allowing venous air to pass directly into the arterial system. Tetralogy of Fallot and pulmonary atresia with VSD both create scenarios where right‑to‑left mixing can occur, again permitting paradoxical or arterial embolization of air.

So, the defect least likely to permit arterial air embolism from venous air is the patent ductus arteriosus, unless it has progressed to Eisenmenger physiology.