If the SA node fails to stimulate electrical impulses, which component usually takes over this function?

When the sinoatrial (SA) node, which is the primary pacemaker of the heart, fails to generate electrical impulses, the atrioventricular (AV) node typically assumes the role of initiating and conducting electrical activity. The AV node has inherent pacemaker activity, albeit at a slower rate than the SA node. This means that it can take over as a secondary pacemaker when necessary, ensuring that the heart continues to beats, albeit less efficiently.

The AV node serves as a critical conduction pathway between the atria and ventricles, allowing for coordinated contraction. If the SA node is not functioning, the AV node can activate impulses around 40-60 beats per minute, which is sufficient to maintain some level of cardiac output. This backup mechanism is essential in times of SA node failure.

In contrast, other options like the Bundle of His and Purkinje fibers can also generate impulses but are typically considered tertiary pacemakers and usually only activate if both the SA and AV nodes fail. The coronary arteries are not involved in the electrical conduction system; they supply blood to the heart muscle itself but do not play a role in initiating electrical impulses.