Which statement best describes third-degree AV block?

Which statement best describes third-degree AV block?

• A. Ventircular bradycardia due to complete atrioventricular dissociation
• B. Prolonged PR interval with dropped beats
• C. Regular rhythm with widened QRS
• D. Normal conduction with atrial tachycardia

Answer: (A)

Third-degree AV block means complete failure of impulses to conduct from the atria to the ventricles. The atria contract driven by the sinus node, while the ventricles are paced independently by an escape rhythm below the block. This creates AV dissociation: there is no fixed relationship between P waves and QRS complexes, and the ventricular rate is slow because it’s set by the escape rhythm. Describing the situation as ventricular bradycardia due to complete AV dissociation captures both the slow ventricular rate and the lack of conduction between atria and ventricles, which is the essence of this block. The QRS can be narrow or wide depending on where the escape rhythm originates, but the key feature is the dissociation.

Third-degree AV block means complete failure of impulses to conduct from the atria to the ventricles. The atria contract driven by the sinus node, while the ventricles are paced independently by an escape rhythm below the block. This creates AV dissociation: there is no fixed relationship between P waves and QRS complexes, and the ventricular rate is slow because it’s set by the escape rhythm. Describing the situation as ventricular bradycardia due to complete AV dissociation captures both the slow ventricular rate and the lack of conduction between atria and ventricles, which is the essence of this block. The QRS can be narrow or wide depending on where the escape rhythm originates, but the key feature is the dissociation.