Third degree AV block is described as

• A. Complete dissociation between atrial and ventricular depolarizations and contractions, ventricular bradycardia
• B. Prolonged PR interval with dropped beats
• C. Widened QRS with regular rhythm
• D. Normal conduction with atrial tachycardia

Answer: (A)

In third-degree AV block there is complete failure of conduction from the atria to the ventricles, so atrial and ventricular activity occur independently. The atria beat at their own rate, while the ventricles rely on a secondary pacemaker below the block, producing a slow, regular escape rhythm. Because no atrial impulse reaches the ventricles, you see AV dissociation: P waves and QRS complexes have no fixed relationship. The resulting bradycardia comes from the slow ventricular escape rhythm. The QRS morphology can be narrow or wide depending on whether the escape focus is near the AV node (narrow) or in the ventricles (wide). This description captures the key features of complete AV block.