What is sinus arrhythmia?

• A. Heart rate is constant
• B. A condition where the heart rate varies with the respiratory cycle.
• C. There is irregular rhythm unrelated to breathing
• D. The heart rate is always rapid

Answer: (B)

Sinus arrhythmia is a normal breathing-related variation in heart rate. The heart's rhythm originates from the sinoatrial node, but the rate changes with respiration: it tends to speed up during inspiration and slow down during expiration. The overall rhythm stays regular; what changes is the interval between beats in sync with breathing. This fluctuation is caused by autonomic nervous system modulation, specifically a shift in vagal tone with breathing, and is particularly common in healthy individuals, especially younger people. The other descriptions—a constant heart rate, an irregular rhythm not tied to breathing, or a heart rate that is always fast—don’t describe this normal breathing-linked pattern.