What is the hallmark of Sinus Bradycardia?

• A. Slower than normal heart rate with a regular rhythm
• B. Regular rhythm with widened QRS
• C. Regular P waves dissociated
• D. Atrial flutter with slow rate

Answer: (A)

Sinus bradycardia is when the sinus node fires at a rate slower than normal, but the rhythm remains organized and sinus-like. The hallmark is a heart rate below 60 beats per minute with a regular rhythm, and typically normal P waves, a normal PR interval, and a narrow QRS complex. This reflects that the impulse still originates from the SA node and conducts through the ventricles as usual, just more slowly.

Why this fits best: a slower-than-normal rate with a regular rhythm directly describes sinus bradycardia. The other scenarios point to different conditions: a widened QRS suggests a ventricular origin or intraventricular conduction delay; regular P waves dissociated indicates AV dissociation or another form of block; atrial flutter with a slow rate shows atrial activity with flutter waves, not true sinus rhythm.