Which rhythm indicates a response to a decrease in SA node activity?

A junctional escape rhythm occurs when there is a decrease in activity from the sinoatrial (SA) node, which is responsible for initiating the heartbeat in a healthy heart. When the SA node fails to generate an impulse adequately or at all, the heart relies on an alternative pacemaker, typically located at the junction of the atria and ventricles, or the atrioventricular (AV) junction, to maintain a basic heart rhythm. This secondary pacemaker generates impulses at a rate that is slower than that of the SA node, leading to a characteristic junctional escape rhythm.

This rhythm is essential because it serves as a protective mechanism; it allows the heart to continue beating even when the primary pacemaker is not functioning properly. In contrast, the other rhythms listed, such as accelerated nodal rhythm, ventricular fusion complex, and supraventricular tachycardia, are not primarily responses to decreased SA node activity. Instead, they involve different mechanisms of impulse generation and do not indicate the same compensatory response to reduced SA node function.