In a normal adult, approximately what percentage of cardiac output depends on the atrial contraction known as the atrial kick?

In a normal adult, approximately what percentage of cardiac output depends on the atrial contraction known as the atrial kick?

• A. 25 percent
• B. 35 percent
• C. 45 percent
• D. 55 percent

Answer: (A)

The atrial kick is the late diastolic push from atrial contraction that finishes filling the ventricle just before systole, increasing preload and thereby boosting stroke volume through the Frank–Starling mechanism. In a normal adult at rest, this atrial contribution accounts for about a quarter of cardiac output. The reason it’s about a quarter is that the atrial contraction adds roughly 10–20 mL of blood per beat to the ventricle; with a typical heart rate around 70–75 beats per minute, that extra volume translates to roughly 1–1.5 L per minute, which is about 20–30% of the total cardiac output, with 25% being a commonly cited average. This preload boost is particularly important when heart rate is high or ventricular compliance is reduced. If the atrial kick is lost (as in atrial fibrillation with rapid rate), cardiac output can fall because the ventricle loses part of its filling and the resulting stroke volume drops.

The atrial kick is the late diastolic push from atrial contraction that finishes filling the ventricle just before systole, increasing preload and thereby boosting stroke volume through the Frank–Starling mechanism. In a normal adult at rest, this atrial contribution accounts for about a quarter of cardiac output. The reason it’s about a quarter is that the atrial contraction adds roughly 10–20 mL of blood per beat to the ventricle; with a typical heart rate around 70–75 beats per minute, that extra volume translates to roughly 1–1.5 L per minute, which is about 20–30% of the total cardiac output, with 25% being a commonly cited average. This preload boost is particularly important when heart rate is high or ventricular compliance is reduced. If the atrial kick is lost (as in atrial fibrillation with rapid rate), cardiac output can fall because the ventricle loses part of its filling and the resulting stroke volume drops.