What is the definition of normal sinus rhythm?

Normal sinus rhythm refers specifically to the rhythmic pattern of electrical impulses generated by the sinoatrial (SA) node in the heart, which is the natural pacemaker. The defining characteristic of normal sinus rhythm is a heart rate that falls within the range of 60 to 100 beats per minute. This range indicates that the heartbeat is neither too slow (bradycardia) nor too fast (tachycardia), allowing for effective circulation and adequate blood flow throughout the body.

Moreover, normal sinus rhythm is characterized not just by the heart rate but also by the following features: each heartbeat originates from the SA node, the P waves preceding each QRS complex are uniform and positive in lead II, and there is a consistent PR interval. These characteristics ensure the heart's rhythm is stable and efficient, allowing proper coordination between atrial and ventricular contraction.

The other options describe rates outside the normal range, indicating potential abnormalities in heart function. For example, a heart rate less than 60 beats per minute would represent bradycardia, and a rate over 100 beats per minute would signify tachycardia. Both conditions might necessitate further assessment to determine their clinical significance.