Under what condition does the atrial kick contribute more to LV filling?

• A. When heart rate is high or LV compliance is reduced.
• B. Only during sleep.
• C. When heart rate is low.
• D. When the LV is hypercompliant.

Answer: (A)

The amount of blood the atrial kick adds to LV filling depends on how much filling the ventricle can do passively during diastole. When the heart rate is high, diastolic filling time is shortened, so there’s less passive filling and the atrial contraction has to contribute more to complete LV filling. Similarly, if the LV is less compliant (stiffer), passive filling is reduced, making the atrial kick more important to achieve adequate preload.

So the atrial kick contributes more to LV filling when the heart rate is high or the LV is less compliant. It’s less critical with a low heart rate and a hypercompliant (very stretchy) LV, where passive filling suffices.