Sinus arrhythmia is usually a sinus rhythm with a rate that varies with respiration (respiratory sinus arrhythmia). It is a benign rhythm disturbance characterized by alternate speeding up and slowing down of the heart rate. Rarely, sinus arrhythmia is not associated with respiration (nonrespiratory sinus arrhythmia).
The SA node discharges irregularly.
The R-R interval is irregular.
Rate: Usually normal (60–100 bpm); frequently increases with inspiration and decreases with expiration
Rhythm: Irregular; varies with respiration
P Waves: Normal (upright and uniform)
PR Interval: Normal (0.12–0.20 sec)
QRS: Normal (0.06–0.10 sec)
**Causes:**
1. Respiratory sinus arrhythmia: Normal finding in children and young adults
2. Nonrespiratory sinus arrhythmia: Cardiac disease and myocardial infarction, especially in association with sinus bradycardia, digoxin therapy, or enhanced vagal tone.
**Treatment:**
Evaluation of the underlying cause
