What is the purpose of an electrocardiogram (ECG)?

• A. To measure heart sounds
• B. To determine the electrical signals of the heart.
• C. To image heart valves
• D. To assess lung function

Answer: (B)

An ECG records the heart's electrical activity over time. Electrodes placed on the skin detect tiny voltage changes as cardiac cells depolarize and repolarize to coordinate each heartbeat. By analyzing the timing and shape of the waves, you can assess heart rate and rhythm, identify conduction abnormalities, and spot signs of ischemia or infarction. This is what the test is designed to measure—the electrical signals driving the heartbeat.

It doesn’t measure heart sounds, which come from valve closures and are heard with a stethoscope; it doesn’t image heart valves, which is done with imaging like echocardiography; and it doesn’t assess lung function, which is evaluated with pulmonary tests.