Basic ECG Interpretation
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).
A sinus rhythm with a resting heart rate of 60 beats per minute or less. The action potential responsible for this rhythm arises from the sinus node and causes a P wave on the surface ECG that is normal in terms of both amplitude and vector. These P waves are typically followed by a normal QRS complex and T wave.