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Definition of sinus arrhythmia (respiratory sinus arrhythmia)
Sinus arrhythmia and respiratory sinus arrhythmia both refer to the same phenomenon. Sinus arrhythmia fulfil all criteria for sinus rhythm except from the fact that the rhythm is slightly irregular (Figure 1). This is mostly a normal (physiological) finding, particularly among young and healthy individuals. The phenomenon is explained by the heart rate variation caused by respiration. The heart rate increases during inspiration due to diminished vagal tone. And the opposite, i.e the heart rate decreases during expiration due to increased vagal tone. This causes the slightly irregular rhythm seen in Figure 1. The rhythm becomes completely regular if the person holds the breath.
However, sinus arrhythmia may be a pathological finding in some cases. Sinus arrhythmia is not a normal finding among older individuals. In that scenario it might be explained by myocardial ischemia (affecting the sinoatrial node), sinus node dysfunction or side effects of digoxin treatment. If the rhythm becomes completely regular when holding the breath, it is likely that the arrhythmia is benign; otherwise further examination is warranted.
Treatment of sinus arrhythmia
Sinus arrhythmia is a normal finding among young and healthy individuals. It is generally not a normal finding among older individuals and might necessitate further examination. If it is caused by underlying heart disease (e.g myocardial ischemia), the treatment is directed at that process.
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This chapters covers ECG criteria and clinical implications of sinus arrhythmia.