Which of the following describes normal sinus rhythm?

Normal sinus rhythm is characterized by several key features, and consistent PR intervals between 0.12 and 0.20 seconds is one of the hallmark indications of this rhythm. The PR interval represents the time it takes for electrical impulses to travel from the atria to the ventricles. In a normal sinus rhythm, the PR interval is typically stable and falls within this range, indicating that the conduction through the AV node is functioning correctly and efficiently.

In contrast, an irregular P-P interval indicates variability in the time between successive P waves, which is not characteristic of a normal sinus rhythm. A heart rate less than 60 bpm would be classified as bradycardia, not normal sinus rhythm, which typically ranges from 60 to 100 bpm. Lastly, a QRS duration greater than 0.12 seconds suggests a delay in ventricular conduction, which could be indicative of either a bundle branch block or other types of dysrhythmias, further deviating from the criteria associated with normal sinus rhythm. Each of these characteristics helps to define the normal sinus rhythm and differentiates it from other arrhythmias.