In third-degree AV block:

• A. Atrial rate and ventricular rate are synchronized
• B. Heart rate 60-100 bpm
• C. AV dissociation with independent atrial and ventricular rhythms and rate around 30-40 bpm
• D. P waves absent

Answer: (C)

In third-degree AV block, there is complete failure of conduction from the atria to the ventricles, so the atria and ventricles beat independently. The atria continue at their own intrinsic rate, while the ventricles rely on a slower escape rhythm originating below the block. This creates AV dissociation with independent atrial and ventricular rhythms, typically with a ventricular rate around 30–40 bpm when the escape focus is in the ventricles. That’s why the best description is AV dissociation with independent atrial and ventricular rhythms and a slow ventricular rate.

Why the other statements aren’t correct: having synchronized atrial and ventricular activity would require some conduction between the chambers, which doesn’t occur in complete block. A normal or higher heart rate (60–100 bpm) reflects normal or near-normal conduction, not complete block. P waves are present and march independently of the QRS complexes; they are not absent, which would imply no atrial activity.