Which rhythm is characterized by irregular R-R intervals?

• A. Normal Sinus Rhythm
• B. Sinus Bradycardia
• C. Sinus Tachycardia
• D. Sinus Arrhythmia

Answer: (D)

R-R interval irregularity is produced by changes in heart rate with the breathing cycle. Sinus arrhythmia occurs when the SA node fires regularly, but the autonomic input linked to respiration causes the intervals between beats to vary—shorter R-R during inspiration and longer R-R during expiration. This creates an overall organized rhythm with normal P waves and PR intervals, but the spacing between beats isn’t constant.

Normal sinus rhythm has regular R-R intervals, and sinus bradycardia or sinus tachycardia maintain regular intervals even though the rate is slow or fast. So, the irregular R-R pattern specifically points to sinus arrhythmia, and it’s a benign variation commonly seen in younger individuals.