What defines sinus bradycardia, and when is intervention considered?

• A. Rate <60 bpm with otherwise normal rhythm; intervene for symptoms or instability (e.g., atropine or pacing per protocol).
• B. Rate >100 bpm with normal rhythm; treat with fluids.
• C. Rate 60-100 bpm with irregular rhythm; administer antiarrhythmics.
• D. Rate <50 bpm with wide QRS; immediate defibrillation.

Answer: (A)

Sinus bradycardia means a true sinus rhythm with a heart rate below 60 beats per minute, while the overall electrical pattern (P waves, regular rhythm, and narrow QRS) remains normal. Intervention is considered when this slow rate causes symptoms or instability—dizziness, syncope, hypotension, chest pain, or altered mental status. In those cases, start with atropine IV (0.5 mg, up to a total of 3 mg), and if there’s no adequate response or if there’s concern for a high‑grade AV block or poor perfusion, proceed to pacing per protocol or use appropriate IV vasoactive support while addressing the underlying cause (such as medication effects or hypothyroidism).

The other scenarios don’t describe sinus bradycardia: a fast heart rate indicates tachycardia; a normal rate with an irregular rhythm points to non-sinus rhythms like atrial fibrillation; bradycardia with a wide QRS often signals a ventricular escape rhythm or conduction disease and is not treated with defibrillation.