In case of a Sinus Arrest, what occurs?

In the case of a sinus arrest, the key event is that the sinoatrial (SA) node fails to initiate an impulse. The SA node is responsible for generating electrical impulses that set the rhythm of the heart, acting as the primary pacemaker. When a sinus arrest occurs, this normal pacing function is disrupted, leading to a temporary cessation of electrical activity in the atria.

This means that the heart does not generate the impulses needed to stimulate contraction in the atrial muscles, which can result in a pause in the heartbeat. An absence of impulses from the SA node may last for several seconds, depending on the condition of the heart and underlying factors affecting the node. During this time, the heart may experience bradycardia or even a complete pause in activity, but the primary aspect of a sinus arrest is the failure of the SA node itself to produce an impulse.

If the pause were to extend, the heart might rely on secondary pacemaking sites (like the AV node or even the Purkinje fibers), but the critical element distinguishing sinus arrest is the specific failure of the SA node to initiate impulses in the first place.