Which structure serves as the backup pacemaker with a typical rate of 40-60 bpm?

Which structure serves as the backup pacemaker with a typical rate of 40-60 bpm?

• A. AV Node, 40-60 bpm
• B. SA Node, 60-100 bpm
• C. Bundle of His, 40-60 bpm
• D. Purkinje Fibers, 14-40 bpm

Answer: (A)

The heart relies on a hierarchy of pacemakers, with the SA node normally setting the rhythm at about 60–100 bpm. If the SA node fails or its signals don’t reach the ventricles, another automatic focus can take over—the AV node. The AV node has an intrinsic firing rate around 40–60 bpm, which is slower than the SA node but fast enough to sustain a heartbeat. This makes it the classic backup pacemaker, or escape rhythm, when the primary pacemaker isn’t driving. In contrast, Purkinje fibers pace much more slowly (roughly 20–40 bpm) and would only take over if both the SA node and AV node failed, which is why they aren’t the usual backup pace. The bundle of His is part of the conduction pathway and doesn’t typically set the rhythm by itself as a backup pacemaker.

The heart relies on a hierarchy of pacemakers, with the SA node normally setting the rhythm at about 60–100 bpm. If the SA node fails or its signals don’t reach the ventricles, another automatic focus can take over—the AV node. The AV node has an intrinsic firing rate around 40–60 bpm, which is slower than the SA node but fast enough to sustain a heartbeat. This makes it the classic backup pacemaker, or escape rhythm, when the primary pacemaker isn’t driving. In contrast, Purkinje fibers pace much more slowly (roughly 20–40 bpm) and would only take over if both the SA node and AV node failed, which is why they aren’t the usual backup pace. The bundle of His is part of the conduction pathway and doesn’t typically set the rhythm by itself as a backup pacemaker.