Which population is sinus arrhythmia most commonly found in?

• A. Common in elderly
• B. Common in newborns
• C. Common in athletes
• D. It is commonly found in children and young adults

Answer: (D)

Sinus arrhythmia is a normal variation in heart rate linked to breathing, caused by cyclical changes in vagal (parasympathetic) tone on the heart's rhythm setting SA node. When you inhale, vagal influence drops and the heart rate speeds up; when you exhale, vagal influence returns and the rate slows down. This respiratory-induced fluctuation is most pronounced in individuals with strong vagal tone, which is typical of children and young adults. As people age, vagal tone tends to decrease and the variation becomes less evident, so sinus arrhythmia is less commonly observed in the elderly. Newborns have developing autonomic control, so the pattern can be less predictable, whereas in children and young adults it shows up more clearly. That’s why this finding is most commonly seen in children and young adults.