sinusrhythmia

Sinus rhythm is the normal heart rhythm generated by the sinoatrial node, producing a P wave before every QRS complex with a normal PR interval. Sinus arrhythmia, typically referred to as respiratory sinus arrhythmia, is a physiological variation in heart rate that occurs within the context of sinus rhythm and is linked to the breathing cycle.

Pathophysiology: The variation is driven by autonomic nervous system modulation, with decreased vagal tone during inspiration increasing heart rate and increased vagal tone during expiration slowing it. The effect is most pronounced in children and young adults and tends to diminish with age or with certain autonomic or structural heart conditions.

Clinical features and diagnosis: Respiratory sinus arrhythmia is usually asymptomatic and considered a normal variant. On ECG, there is a consistent P wave and QRS complex for each beat, but the interval between beats (RR interval) lengthens with expiration and shortens with inspiration. It may be more evident during Holter monitoring or exercise testing and typically disappears with breath holding.

Differential diagnosis: Distinguish RSA from atrial fibrillation (no identifiable P waves and irregularly irregular rhythm) and from wandering atrial pacemaker (varying P wave morphology and PR interval). It should not be mistaken for pathological tachyarrhythmias or bradyarrhythmias when no symptoms are present.

Management and prognosis: RSA is benign and usually requires no treatment. It may be considered a sign of good autonomic tone in young individuals. Evaluation focuses on ruling out underlying cardiac or systemic disease if symptoms or atypical features are present.