Sinusarrhythmia

Sinus arrhythmia, often referred to as respiratory sinus arrhythmia, is a normal physiological variation in heart rate that occurs with the breathing cycle. In healthy individuals, the heart rate tends to rise during inspiration and fall during expiration, producing a rhythmic pattern of short and long intervals between heartbeats.

Mechanism involves the autonomic nervous system, particularly vagal (parasympathetic) tone. Inspiration reduces vagal influence on the sinus node, allowing the heart to beat faster, while expiration increases vagal activity and slows the rate. The result is cyclic changes in the R-R interval that are synchronized with respiration. The effect is more pronounced in children and young adults and tends to diminish with age or in certain disease states that affect autonomic function.

Clinical features are typically absent or minimal. On an electrocardiogram, the R-R intervals vary in a regular, breathing-correlated manner, while the P waves and QRS complexes remain normal. There is no ectopy or evidence of an abnormal pacemaker.

Diagnosis is usually made by observing RR interval variation on ECG or during Holter monitoring and correlating it with the patient’s breathing pattern. In most cases, the variation is a benign, expected finding rather than a sign of cardiac disease.

Significance lies in its use as a noninvasive indicator of vagal tone and autonomic function, particularly in research and in assessing cardiovascular fitness. While RSA can be attenuated with age or autonomic impairment, in healthy individuals it reflects robust parasympathetic control.