Which structure is the primary pacemaker of the heart and its typical rate?

Which structure is the primary pacemaker of the heart and its typical rate?

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

Answer: (A)

The heart’s rhythm is controlled by specialized cells in the conduction system, and the one that sets the pace is the sinoatrial (SA) node. It has the fastest intrinsic firing rate, so its impulses determine the heart’s regular rhythm under normal conditions. This results in a typical resting rate of about 60–100 beats per minute. Other pacemakers in the AV node and Purkinje fibers have slower intrinsic rates (AV node roughly 40–60 bpm, Purkinje even slower), so they only take over if the SA node fails. That’s why the SA node is the primary pacemaker and why its typical rate is 60–100 bpm.

The heart’s rhythm is controlled by specialized cells in the conduction system, and the one that sets the pace is the sinoatrial (SA) node. It has the fastest intrinsic firing rate, so its impulses determine the heart’s regular rhythm under normal conditions. This results in a typical resting rate of about 60–100 beats per minute. Other pacemakers in the AV node and Purkinje fibers have slower intrinsic rates (AV node roughly 40–60 bpm, Purkinje even slower), so they only take over if the SA node fails. That’s why the SA node is the primary pacemaker and why its typical rate is 60–100 bpm.