What defines a normal sinus rhythm?

A normal sinus rhythm is characterized primarily by a heart rate that falls within the range of 60-100 beats per minute, along with specific characteristics associated with the P wave. In a normal sinus rhythm, each P wave represents atrial depolarization originating from the sinoatrial (SA) node, which is the natural pacemaker of the heart. These P waves are typically upright in leads I, II, and aVF, and there is a consistent relationship between the P waves and QRS complexes, indicating that every P wave is followed by a QRS complex in a 1:1 ratio.

This coherence in rhythm, heart rate, and P wave presence and morphology is critical in determining that the heart is operating normally under sinus control. If the heart rate falls below 60 beats per minute or exceeds 100 beats per minute, or if there are absent, inverted, or otherwise abnormal P waves, the rhythm would not be classified as a normal sinus rhythm. Hence, the option that states a heart rate of 60-100 bpm with specific P wave characteristics accurately captures the essence of what constitutes a normal sinus rhythm.

Understanding these criteria is essential for identifying other arrhythmias and recognizing when a patient's heart rhythm deviates from normal