What characterizes sinus tachycardia?

Sinus tachycardia is characterized by the sinus node retaining its role as the primary pacemaker of the heart while discharging electrical impulses at a rate that is faster than normal. This increased rate typically ranges from 100 to 180 beats per minute. In this condition, despite the higher heart rate, the rhythm remains regular, meaning that the impulses are generated in a consistent pattern.

The other options highlight incorrect mechanisms that do not align with the nature of sinus tachycardia. For example, a slow discharge from the SA node is indicative of bradycardia, not tachycardia. An irregular impulse discharge would suggest the presence of arrhythmias, while an absence of SA node activity points toward other pacemaker mechanisms taking over the heart's rhythm, which contradicts the defining characteristics of sinus tachycardia. Thus, the essence of sinus tachycardia focuses on the rapid but regular discharge from the SA node.