electrocardogram

An electrocardiogram (ECG or EKG) is a noninvasive test that records the electrical activity of the heart over a short period, typically a few seconds. Electrical impulses produced by cardiac muscle as it depolarizes and repolarizes are detected by adhesive electrodes placed on the chest, arms, and legs. The signals are amplified and displayed as a waveform on a monitor or paper. A standard 12-lead ECG provides multiple viewpoints of the heart’s electrical activity, while single-lead or few-lead systems are used for continuous or portable monitoring.

The ECG measures heart rate and rhythm and assesses conduction through the atrioventricular node and other pathways. It records intervals such as PR, QRS, and QT, and identifies waveform abnormalities including ST-segment changes, T-wave inversions, and pathological Q waves. These features help detect myocardial ischemia or infarction, electrolyte disturbances, chamber enlargement, and other cardiac conditions. The test is interpreted in the context of symptoms and clinical history.

Procedures and variants include resting ECG, ambulatory monitoring with a Holter device (usually 24–48 hours), extended event monitors for less frequent events, and exercise or treadmill stress testing with ECG to evaluate cardiac response to exertion. Patch-based continuous monitors and implantable loop recorders are used for longer-term observation.

Limitations include the snapshot nature of the recording, potential artifacts from movement or poor electrode contact, and the need for clinical correlation since an ECG cannot measure mechanical heart function. History recognizes the technique’s development in the early 20th century, notably by Willem Einthoven, with the 12-lead system becoming a standard diagnostic tool in modern medicine.