Which of the following characteristics indicates a normal sinus rhythm?

A normal sinus rhythm is characterized by several key features that collectively indicate a healthy cardiac electrical activity originating from the sinus node. Firstly, the heart rate is typically within the range of 60 to 100 beats per minute, which is considered the normal range for adults at rest. This range reflects the automaticity of the sinus node, which is responsible for initiating each heartbeat.

Additionally, in a normal sinus rhythm, the R wave—part of the QRS complex on an electrocardiogram—occurs at consistent intervals. This uniformity is crucial as it reflects regular atrial and ventricular contractions, allowing the heart to maintain effective blood circulation. Irregularities in the R-R intervals can indicate arrhythmias or other cardiac issues.

Furthermore, the PR interval, which represents the time it takes for electrical impulses to travel from the atria to the ventricles, should be between 0.12 to 0.20 seconds in a normal sinus rhythm. This value indicates proper conduction through the atrioventricular (AV) node, ensuring timely contraction of the ventricles following atrial contraction.

Therefore, since all these characteristics—the heart rate, regularity of the R wave, and the appropriate PR interval—are critical components of a normal sinus