In junctional rhythm pathophysiology, which pacemaker typically takes over when the SA node fails?

In junctional rhythm pathophysiology, which pacemaker typically takes over when the SA node fails?

• A. SA node remains the primary pacemaker
• B. AV node takes over as the pacemaker
• C. Atria initiate beats independently
• D. Ventricles generate the pacemaking impulse

Answer: (B)

When the primary pacemaker fails, the heart relies on a backup faster or slower pacemaker within the conduction system. In a junctional rhythm, the AV node takes over as the pacing source. The AV node’s intrinsic rate is about 40–60 beats per minute, slower than the SA node, so the heart rhythm slows accordingly. Because the impulse starts in the AV node, atrial activation can be retrograde or delayed, so P waves may appear inverted or may even be hidden within or just after the QRS. Despite this, ventricular conduction remains normal, giving a narrow QRS complex. This combination—AV nodal origin with a 40–60 bpm rate and possible absent/inverted P waves—refers to a junctional rhythm. If the SA node were still the primary pacemaker, we wouldn’t describe a junctional rhythm. If the atria were initiating beats independently, that would be an atrial rhythm rather than junctional. If the ventricles were generating the impulse, the rhythm would be a ventricular escape with a much slower rate and wide QRS.

When the primary pacemaker fails, the heart relies on a backup faster or slower pacemaker within the conduction system. In a junctional rhythm, the AV node takes over as the pacing source. The AV node’s intrinsic rate is about 40–60 beats per minute, slower than the SA node, so the heart rhythm slows accordingly.

Because the impulse starts in the AV node, atrial activation can be retrograde or delayed, so P waves may appear inverted or may even be hidden within or just after the QRS. Despite this, ventricular conduction remains normal, giving a narrow QRS complex. This combination—AV nodal origin with a 40–60 bpm rate and possible absent/inverted P waves—refers to a junctional rhythm.

If the SA node were still the primary pacemaker, we wouldn’t describe a junctional rhythm. If the atria were initiating beats independently, that would be an atrial rhythm rather than junctional. If the ventricles were generating the impulse, the rhythm would be a ventricular escape with a much slower rate and wide QRS.