Which statement best describes why the superior vena cava can show pulsatility on Doppler in relation to anatomy?

• A. Proximity to the right atrium causes pulsatility, with respiratory phasicity supersimposed
• B. Pulsatility is solely due to inspiration
• C. Pulsatility is never observed in the SVC
• D. Pulsatility is caused only by arterial pressure waves

Answer: (A)

Pulsatility in the superior vena cava comes from the heart’s influence on nearby vessels. The SVC sits right against the right atrium, so the pressure and flow changes that occur during the cardiac cycle are transmitted into the SVC. As the atrium contracts and relaxes, these transmitted pressure waves create a pulsatile Doppler signal in the SVC that is synchronized with the heartbeat. Breathing can add some variation (respiratory phasicity), but the primary driver is the cardiac activity of the right atrium. It isn’t caused by inspiration alone, and arterial pressure waves don’t generate this venous pulsatility.