Normal Sinus Rhythm

Normal Sinus Rhythm (NSR) Overview

  • 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.
ECG Normal sinus rhythm strip

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.

Example ECG

ECG Normal sinus rhythm

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.

Related Topics


LITFL Further Reading


Advanced Reading


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ECG LIBRARY

Electrocardiogram

Emergency Physician in Prehospital and Retrieval Medicine in Sydney, Australia. He has a passion for ECG interpretation and medical education | ECG Library |

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