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.

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

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

• The P wave
• Sinus arrhythmia
• Sinus bradycardia
• Sinus tachycardia

LITFL Further Reading

• ECG Library Basics – Waves, Intervals, Segments and Clinical Interpretation
• ECG A to Z by diagnosis – ECG interpretation in clinical context
• ECG Exigency and Cardiovascular Curveball – ECG Clinical Cases
• 100 ECG Quiz – Self-assessment tool for examination practice
• ECG Reference SITES and BOOKS – the best of the rest

Advanced Reading

• Brady WJ, Truwit JD. Critical Decisions in Emergency and Acute Care Electrocardiography
• Surawicz B, Knilans T. Chou’s Electrocardiography in Clinical Practice: Adult and Pediatric
• Wagner GS. Marriott’s Practical Electrocardiography 12e
• Chan TC. ECG in Emergency Medicine and Acute Care
• Rawshani A. Clinical ECG Interpretation
• Mattu A. ECG’s for the Emergency Physician
• Hampton JR. The ECG In Practice, 6e