Sinus arrhythmia

Sinus arrhythmia is the variation in heart rate by more than 0.16 second. Respiratory sinus arrhythmia is the more common type, in which the heart rate is synchronized with breathing, slowing with expiration and accelerating with inspiration.

Sinus arrhythmia is usually cyclic because it is respiratory related, resulting in increase in sinus rate with inspiration and decrease in rate with expiration.

The cause of sinus arrhythmia is physiologic, but it may be drug induces (e.g digoxin). Marked sinus arrhythmia may be a manifestation of the sick sinus syndrome.

Sinus arrhythmia is very common in young children and disappears as they get older. In general, the rhythm also tends to disappear when the rate increases, as occurs, for example, with atropine or with exercise.

There are two kinds of sinus arrhythmia: the respiratory or phasic variant, which occurs during normal circumstances, and the non-respiratory or nonphasic variant, which is only found in a pathological states.
Sinus arrhythmia