Which electrocardiogram feature indicates the sinus node is firing?

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Multiple Choice

Which electrocardiogram feature indicates the sinus node is firing?

Explanation:
The P wave reflects atrial depolarization driven by the impulse from the sinus node. When the SA node fires, it initiates atrial depolarization, which appears on the ECG as a P wave before each QRS complex. Seeing a P wave before every beat indicates the heart’s natural pacemaker is initiating the rhythm, i.e., normal sinus rhythm. In contrast, the QRS complex shows ventricular depolarization, the T wave shows ventricular repolarization, and the U wave, when present, is a less common late repolarization feature not tied to SA node firing.

The P wave reflects atrial depolarization driven by the impulse from the sinus node. When the SA node fires, it initiates atrial depolarization, which appears on the ECG as a P wave before each QRS complex. Seeing a P wave before every beat indicates the heart’s natural pacemaker is initiating the rhythm, i.e., normal sinus rhythm. In contrast, the QRS complex shows ventricular depolarization, the T wave shows ventricular repolarization, and the U wave, when present, is a less common late repolarization feature not tied to SA node firing.

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