Which characteristic is commonly present in sinus arrhythmia?

Sinus arrhythmia is characterized by an irregular rhythm that varies with the respiratory cycle. As a person inhales, heart rate may increase, and as they exhale, it may decrease. This fluctuation is due to the influence of the autonomic nervous system on heart rate regulation, particularly the vagus nerve's response to breathing patterns.

The nature of sinus arrhythmia is typically benign, especially in young, healthy individuals, and reflects the heart's normal response to varying levels of activity and pressure changes during respiration. This phenomenon indicates healthy autonomic control of the heart, which is a desirable physiological response.

In contrast, a consistent heart rate would indicate a stable rhythm rather than the variability observed in sinus arrhythmia. Persistent tachycardia suggests an abnormally high heart rate that is not aligned with the respiratory cycle. Uniform P wave morphology can indicate normal sinus rhythm but does not reflect the irregularity characteristic of sinus arrhythmia, where the P waves may still be normal in shape but occur at irregular intervals.