What is classified as Normal Sinus Rhythm (NSR)?

Normal Sinus Rhythm (NSR) is characterized by a heartbeat that originates from the sinoatrial (SA) node, which is responsible for initiating the electrical impulses that regulate the heart's rhythm. The SA node typically generates a heart rate of approximately 60 to 100 beats per minute (bpm) at rest, reflecting the normal physiological range for a healthy adult.

The second option you selected emphasizes that the heartbeat originates specifically from the SA node, and it also mentions the typical rate of around 70 bpm, aligning with the normal functioning of the heart when a person is at rest. This is a key characteristic of NSR, illustrating that the heart maintains an appropriate rate and rhythm under resting conditions.

In contrasting this with the other options, the first option lists a heart rate of 50-70 bpm, which does not fully capture the accepted range for NSR, as a typical resting rate should generally not fall below 60 bpm. The third option indicates a fluctuating heart rate between 60-100 bpm, which implies variability; however, NSR is defined by a consistent pattern, not just the presence of variability within the range. The last option describes a rhythm originating from the ventricles, which is indicative of a pathological