How would you recognize normal sinus rhythm on ECG?

• A. Irregular rhythm with absent P waves.
• B. Regular rhythm 60-100 bpm with P waves before each QRS and a PR interval 0.12–0.20 s.
• C. Irregular rhythm with prolonged PR.
• D. Regular rhythm >100 bpm with no P waves.

Answer: (B)

Normal sinus rhythm means the heart’s electrical impulse starts in the sinus node and follows a normal sequence: every atrial depolarization (P wave) is followed by a ventricular depolarization (QRS); the rhythm is regular; the rate is 60–100 bpm; the PR interval is 0.12–0.20 seconds; and the QRS is narrow. In other words, you should see a P wave before each QRS, with uniform P waves, and a consistent, evenly spaced rhythm within the 60–100 bpm range and a PR interval in the normal range. The presence of a P wave before every QRS confirms atrial activation properly conducted to the ventricles, and a normal PR interval shows intact AV conduction.

If an ECG shows an irregular rhythm with no P waves, that points to atrial fibrillation rather than normal sinus rhythm. A prolonged PR interval indicates a first-degree AV block, which disrupts normal conduction timing. A regular rhythm faster than 100 bpm with no P waves suggests a non-sinus tachycardia, not normal sinus rhythm.