- The default heart rhythm.
- Pacemaking impulses arise from the sino-atrial node and are transmitted to the ventricles via the AV-node and His-Purkinje system.
- This results in a regular, narrow-complex heart rhythm at 60-100 bpm.
Characteristics of normal sinus rhythm
- Regular rhythm at a rate of 60-100 bpm (or age-appropriate rate in children).
- Each QRS complex is preceded by a normal P wave.
- Normal P wave axis: P waves should be upright in leads I and II, inverted in aVR.
- The PR interval remains constant.
- QRS complexes are < 100 ms wide (unless a co-existent interventricular conduction delay is present).
Normal heart rates in children
- Newborn: 110 – 150 bpm
- 2 years: 85 – 125 bpm
- 4 years: 75 – 115 bpm
- 6 years+: 60 – 100 bpm
Variations on sinus rhythm
- Sinus tachycardia = sinus rhythm with resting heart rate > 100 bpm in adults, or above the normal range for age in children.
- Sinus bradycardia = sinus rhythm with resting heart rate < 60 bpm in adults, or below the normal range for age in children.
- Sinus arrhythmia = sinus rhythm with a beat-to-beat variation in the P-P interval (the time between successive P waves), producing an irregular ventricular rate.
Normal sinus rhythm in a healthy 18-year old male:
- Regular rhythm at 84 bpm.
- Normal P wave morphology and axis (upright in I and II, inverted in aVR).
- Narrow QRS complexes (< 100 ms wide).
- Each P wave is followed by a QRS complex.
- The PR interval is constant.
- Chan TC, Brady WJ, Harrigan RA, Ornato JP, Rosen P. ECG in Emergency Medicine and Acute Care. Elsevier Mosby 2005.
- Surawicz B, Knilans TK. Chou’s Electrocardiography in Clinical Practice. 6th Edition. Saunders Elsevier 2008.