ECG RHYTHM LAB

Sinus Arrhythmia

Sinus beats show a gradual cyclical change in R–R intervals.

Generated six-second Lead II example · 72 bpm target rate · not a patient recording.

Typical rate

Varies with the cycle

Regularity

Cyclic variation

P waves

Upright; one per QRS

PR interval

Constant

QRS

Narrow, <120 ms

What to look for

Normal P–QRS relationships with repeating, gradual changes in spacing.

Show this rhythm

Sources and limitations