Which term describes the normal rhythm with the sinus node initiating impulses?

• A. PR interval
• B. P wave
• C. QRS complex
• D. NSR

Answer: (D)

The idea is recognizing a normal heart rhythm that starts in the sinus (SA) node. Normal sinus rhythm means the heart rate is in the normal range, the rhythm is regular, and each impulse originates from the SA node. In an ECG this shows as a P wave before every QRS complex, with a normal PR interval and a narrow QRS complex, indicating proper atrial and ventricular conduction.

This term is best because it specifically describes both the regular rhythm and the SA node as the initiator of impulses. The other items refer to parts of the ECG or a single measurement: the PR interval is the time from the start of the P wave to the start of the QRS, reflecting atrioventricular conduction; the P wave is atrial depolarization; the QRS complex is ventricular depolarization. None alone defines the overall normal, SA node–driven rhythm, so NSR is the most accurate term.