Sinus arrhythmia

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-in-Chief: Rim Halaby, M.D. [2]; Mahmoud Sakr, M.D. [3]


Sinus arrhythmia is an irregularity of the sinus rhythm defined as a variation in the P-P interval by 0.16 sec (160 msec) or more in the presence of normal P waves. It is the most common type of arrhythmia and it is classified mainly into respiratory sinus arrhythmia and non-respiratory sinus arrhythmia. While respiratory sinus arrhythmia is a normal variant that is mostly common in young and disappears with age,[1] the non-respiratory sinus arrhythmia is most commonly present among elderly with heart disease. Sinus arrhythmia occurs with slower heart rates or after enhanced vagal tone, and tends to disappear with increase in the heart rate.[2] Triggers for sinus arrhythmia include sinoatrial block, sinus pause, premature atrial beat, carotid massage, and administration of parasympathomimetic medications.


Respiratory Sinus Arrhythmia

Respiratory sinus arrhythmia is associated with variations in the heart rate with the respiratory cycle secondary to changes in the vagal tone (heart rate increases in inspiration and decreases in expiration). It is a normal variant that is most present in young people.

To read more about respiratory sinus arrhythmia, click here.

Non-respiratory Sinus Arrhythmia

  • In non-respiratory sinus arrhythmia, the variation in the P-P interval is unrelated to the respiratory cycle. It can occur in the normal heart; however, it is more common among elderly with heart disease. The cause of non-respiratory sinus arrhythmia is usually unknown, known causes include:
  • Side effect of medications (digitalis, morphine)
  • High intracranial pressure
  • Inferior myocardial infarction
  • Recovery from illnesses

Ventriculophasic Sinus Arrhythmia

A ventriculophasic sinus arrhythmia occurs most often in patients with partial or complete AV block, but it's also observed after a compensatory pause induced by a premature ventricular contraction.[3]

The P-P interval that does not contain the QRS complex is longer than that containing the QRS complex.

Wandering of the Pacemaker within the SA Node

ECG characteristics:

  • Variable P-P interval
  • Variable amplitude of the P wave
  • Variable morphology of the P wave
  • Variable PR interval (not always)


  1. Kaushal P, Taylor JA (2002). "Inter-relations among declines in arterial distensibility, baroreflex function and respiratory sinus arrhythmia". J Am Coll Cardiol. 39 (9): 1524–30. PMID 11985918.
  2. Masi CM, Hawkley LC, Rickett EM, Cacioppo JT (2007). "Respiratory sinus arrhythmia and diseases of aging: obesity, diabetes mellitus, and hypertension". Biol Psychol. 74 (2): 212–23. doi:10.1016/j.biopsycho.2006.07.006. PMC 1804292. PMID 17034928.
  3. de Marchena E, Colvin-Adams M, Esnard J, Ridha M, Castellanos A, Myerburg RJ (2003). "Ventriculophasic sinus arrhythmia in the orthotopic transplanted heart: mechanism of disease revisited". Int J Cardiol. 91 (1): 71–4. PMID 12957731.