What does an electrocardiogram (ECG) do?

• A. Measures blood pressure continuously.
• B. Records electrical changes sent by conduction impulses as picked up by electrodes.
• C. Visualizes heart chamber anatomy.
• D. Measures heart sounds.

Answer: (B)

An ECG directly records the heart’s electrical activity produced by the cardiac conduction system as it’s detected by surface electrodes. This electrical activity drives the timing of heart muscle contractions, and the ECG translates those impulses into recognizable waves—the P wave for atrial depolarization, the QRS complex for ventricular depolarization, and the T wave for ventricular repolarization. That direct link to electrical changes is why this test is described as measuring electrical activity with leads placed on the skin. The other options describe different kinds of information: blood pressure monitoring measures pressure in the vessels, imaging like ultrasound or other modalities visualizes anatomy, and heart sounds come from valve motion detected by auscultation, not electrical activity.