Sinus arrhythmia
Definition
A sinus rhythm (normal sinus P waves, upright in leads I, II and aVF) in which the P-P and R-R intervals vary from beat to beat; the 2022 Brazilian ECG guideline characterizes it by a variation in P-P intervals of 160 to 220 ms. In the common respiratory (phasic) form the R-R interval shortens during inspiration and lengthens during expiration, reflecting respiratory modulation of cardiac vagal activity. It is usually a physiologic finding, very frequent in children, and a normal finding in athletes.
Clinical noteP-wave morphology and the PR interval stay constant, which distinguishes it from a wandering atrial pacemaker or other ectopic atrial rhythms.
Sources
- Samesima N, God EG, Kruse JCL, et al. Brazilian Society of Cardiology guidelines on the analysis and issuance of electrocardiographic reports - 2022. Arq Bras Cardiol. 2022;119(4):638-680. doi.org/10.36660/abc.20220623
- Yasuma F, Hayano J. Respiratory sinus arrhythmia: why does the heartbeat synchronize with respiratory rhythm? Chest. 2004;125(2):683-690. doi.org/10.1378/chest.125.2.683
- Singh RK. Electrical injury and wandering atrial pacemaker. Cureus. 2021;13(9):e18335. doi.org/10.7759/cureus.18335
Last reviewed 2 October 2026. Every definition in the EKG Dictionary cites the guideline, consensus statement or original paper it comes from.