If the SA Node does not fire, which rhythm may be present?

When the SA node fails to fire, the heart relies on lower pacemakers to initiate an electrical impulse. In this scenario, a junctional rhythm is often the result. The junctional rhythm originates from the atrioventricular (AV) node or junctional tissue, which takes over the role of pacing the heart when the SA node is not functioning. This leads to a heart rate that is typically slower than normal, often between 40 and 60 beats per minute, and can result in a distinct rhythm pattern on an electrocardiogram (ECG), characterized by absent or inverted P waves.

Understanding the function of the heart’s electrical conduction system is crucial. The SA node is the primary pacemaker, but if it is inactive, other pacemaker cells, like those in the AV node, will attempt to maintain some level of heart rhythm, hence the junctional rhythm comes into play as the next passive pacing mechanism. This knowledge emphasizes the importance of recognizing different heart rhythms based on the location of impulse generation in the heart and their physiological implications.