Why is TGV so serious?

Why is TGV so serious?

• A. Oxygenated and non-oxygenated blood do not go where they are needed; they must mix to supply oxygen
• B. Oxygenated and non-oxygenated blood remain separate and never mix
• C. Mixing occurs spontaneously at all times
• D. TGV causes over-oxygenation of systemic circulation

Answer: (A)

In transposition of the great vessels, the aorta comes from the right ventricle and the pulmonary artery comes from the left ventricle, so the systemic and pulmonary circuits run in parallel rather than in series. That means the blood returning to the heart from the body (deoxygenated) is kept separate from the blood going to the lungs (oxygenated). For tissues to receive adequate oxygen, mixing of these two streams must occur through shunts such as a patent foramen ovale, patent ductus arteriosus, or a ventricular septal defect. Without that mixing, the systemic circulation receives largely desaturated blood, leading to severe hypoxemia and cyanosis. So the best statement recognizes that mixing is essential to supply oxygen to the body's tissues in this condition. The other ideas are less accurate: if the streams never mixed, survival would be unlikely; mixing occurring all the time isn’t the correct description of the physiology; and the problem is not over-oxygenation of the systemic circulation but insufficient oxygen delivery due to parallel circulation.

In transposition of the great vessels, the aorta comes from the right ventricle and the pulmonary artery comes from the left ventricle, so the systemic and pulmonary circuits run in parallel rather than in series. That means the blood returning to the heart from the body (deoxygenated) is kept separate from the blood going to the lungs (oxygenated). For tissues to receive adequate oxygen, mixing of these two streams must occur through shunts such as a patent foramen ovale, patent ductus arteriosus, or a ventricular septal defect. Without that mixing, the systemic circulation receives largely desaturated blood, leading to severe hypoxemia and cyanosis.

So the best statement recognizes that mixing is essential to supply oxygen to the body's tissues in this condition. The other ideas are less accurate: if the streams never mixed, survival would be unlikely; mixing occurring all the time isn’t the correct description of the physiology; and the problem is not over-oxygenation of the systemic circulation but insufficient oxygen delivery due to parallel circulation.