Final answer:
An electrocardiogram (ECG) measures the electrical activity of the heart, specifically the voltages created by depolarization and repolarization of the cardiac muscle. The typical setup uses a 12-lead system, with the lead II potential being commonly used for diagnosis, and it helps to determine heart rate and diagnose abnormal heart functions.
Step-by-step explanation:
An electrocardiogram (ECG or EKG) measures the electrical activity of the heart by recording the voltages created by depolarization and repolarization waves through the cardiac muscle. This test is performed using electrodes placed on the skin, typically using a 12-lead setup, although some ECGs use fewer leads; a standard three-lead ECG from years past would've placed electrodes on the left and right arms and the left leg. The voltage measured between the right arm and the left leg is known as the lead II potential, which is commonly graphed due to its informative value about heart function. An ECG shows a tracing of the electrical signals, which can reveal both normal and abnormal heart functions, making it an essential tool for diagnosis. The components, segments, and intervals on a normal ECG tracing correlate to specific electrical events that are related to the contraction of the heart muscle.The ability to determine the heart rate from an ECG is another crucial aspect, done by measuring the time between the beats on the tracing. Traditionally, an electrocardiograph (the instrument generating the ECG) utilizes 3, 5, or 12 leads, with the 12-lead providing the most information. When continuous monitoring is needed, a portable device called a Holter monitor can be used, which records heart activity for an extended period, such as 24 hours during the patient's everyday routine.