AEMCA Practice Exam

Why does sinus arrhythmia commonly occur in young adults and children?

1. It results from a high resting heart rate.

2. Increased vagal tone caused by changing thoracic pressure.

3. It is a genetic condition.

4. It's primarily due to nervous system disorders.

The correct answer is: Increased vagal tone caused by changing thoracic pressure.

Sinus arrhythmia commonly occurs in young adults and children primarily due to increased vagal tone, which is influenced by changing thoracic pressure during respiration. As these individuals breathe in, the increased lung volume reduces intrathoracic pressure and increases venous return to the heart, leading to a transient increase in heart rate. Conversely, when they exhale, the opposite occurs—heart rate may decrease as the vagal tone increases. This phenomenon is a normal physiological response, especially observed in younger populations whose autonomic nervous systems may be more responsive and dominant. The other choices do not accurately explain this common occurrence. A high resting heart rate is not directly related to sinus arrhythmia but rather to the overall heart rhythm pattern. A genetic condition would imply a hereditary basis for sinus arrhythmia that is not typically seen; instead, it is linked to the heart's natural response to breathing patterns. Lastly, attributing sinus arrhythmia primarily to nervous system disorders undermines its status as a normal variant in healthy young individuals rather than a pathological condition.