Which statement correctly identifies pacemaker locations?

• A. Atrioventricular node and Purkinje network
• B. Sinoatrial node and atrioventricular node
• C. Bundle of His and Purkinje fibers
• D. Atrial and ventricular myocytes

Answer: (B)

The heart’s rhythm is set by specialized pacemaker tissues that can generate spontaneous electrical impulses. The primary pacemaker is the Sinoatrial node, located in the high right atrium near the superior vena cava, which normally sets the pace. If the SA node fails, the Atrioventricular node in the right atrial–ventricular septum near the tricuspid valve can take over as a slower secondary pacemaker. The rest of the conduction system, including the Bundle of His and Purkinje fibers, mainly transmits impulses to the ventricles rather than initiating the rhythm. Atrial and ventricular myocytes are contractile cells and do not serve as normal pacemakers. Because of this, naming the Sinoatrial node and Atrioventricular node as pacemaker locations correctly identifies the primary and secondary rhythm-setting tissues.