How is a sinus arrhythmia primarily caused?

A sinus arrhythmia is primarily characterized by variations in heart rate that occur with the phases of breathing. It is a normal physiological response where the heart rate increases with inhalation and decreases with exhalation. This phenomenon is most pronounced in children and decreases with age.

The influence of the respiratory cycle on heart rate is due to the interaction of the autonomic nervous system, particularly the vagus nerve, which increases heart rate during inhalation and decreases it during exhalation. This aligns well with the concept of sinus arrhythmia being a natural and benign variation rather than a pathological condition.

Other options do not typically account for sinus arrhythmia. Heart block suggests a disruption in electrical impulses but does not cause the rhythmic breathing-related changes characteristic of sinus arrhythmia. Medication effects can induce various arrhythmias, but they do not relate specifically to sinus arrhythmia. Similarly, while stress can affect heart rate, it is not the primary driver behind the sinus arrhythmia observed during the respiratory cycle.