What does the term sinus describe in heart rhythm?

• A. The electrical signal to start the heart beating originates in the sinus node.
• B. The electrical impulse originates from the AV node.
• C. Sinus rhythm refers to any abnormal rhythm.
• D. Sinus is the name of a heart chamber.

Answer: (A)

Sinus refers to the sinoatrial node, the heart’s natural pacemaker, located in the right atrium near the opening of the superior vena cava. This node spontaneously generates the electrical impulse that starts each heartbeat and sets the heart’s pace. The impulse then travels through the atria to the atrioventricular node and onward to the ventricles, producing the normal rhythm. When the impulse originates from the SA node, the rhythm is called sinus rhythm, which is considered normal as long as the rate and conduction are appropriate. If impulses came from the AV node or other ectopic sites, the rhythm would not be sinus, and sinus is also not a name for a heart chamber.