Third-degree AV block results in which physiologic state?

Third-degree AV block results in which physiologic state?

• A. Atrioventricular junctional rhythm with constant P-P
• B. Progressive AV block with variable PR lengths
• C. Complete AV block with AV dissociation
• D. P waves occur independent of QRS

Answer: (C)

In third-degree AV block, conduction from the atria to the ventricles is completely interrupted, so the atria and ventricles beat independently. The atria are paced by the SA node, producing P waves at a regular rate, while the ventricles rely on an intrinsic escape rhythm below the block, which is slower. This independent activity creates AV dissociation, where P waves occur with a constant P–P interval but have no fixed relationship to the QRS complexes. Depending on where the escape rhythm originates, the QRS can be narrow (junctional escape) or wide (ventricular escape). This combination—AV dissociation with no conduction from atria to ventricles—is the hallmark state.

In third-degree AV block, conduction from the atria to the ventricles is completely interrupted, so the atria and ventricles beat independently. The atria are paced by the SA node, producing P waves at a regular rate, while the ventricles rely on an intrinsic escape rhythm below the block, which is slower. This independent activity creates AV dissociation, where P waves occur with a constant P–P interval but have no fixed relationship to the QRS complexes. Depending on where the escape rhythm originates, the QRS can be narrow (junctional escape) or wide (ventricular escape). This combination—AV dissociation with no conduction from atria to ventricles—is the hallmark state.