Electrocardiogram

An electrocardiogram (ECG) is a recording of voltage changes produced by the heart’s electrical activity over time. Its waveforms help assess heart rhythm, conduction, and signs of cardiac injury.

Cardiac action potential: A temporary change in cardiac-cell membrane voltage that initiates contraction or electrical signaling. Its changing voltages generate the electrical signals detected at the body surface.
Cardiac arrhythmia: Any disturbance in the rate, regularity, or electrical origin of the heartbeat. ECG recordings classify abnormal rhythms by their electrical patterns.
Cardiac conduction system: The specialized tissues that initiate and conduct electrical impulses through the heart. Its activation sequence determines the order of ECG waveforms.
Echocardiography: Ultrasound imaging that depicts the heart’s structure, movement, and blood flow. It shows mechanical function and anatomy rather than recording surface voltage.
Augustus Waller: A British physiologist who made early human electrocardiographic recordings in the late nineteenth century. His experiments demonstrated that cardiac electrical activity could be recorded from the body surface.
Electrocardiographic lead: A particular electrical viewpoint created by electrodes placed at defined locations on the body. Each lead records a different projection of the heart’s electrical activity.
Atrial fibrillation: A common arrhythmia marked by disorganized atrial electrical activity and an irregular heartbeat. Its characteristic irregular rhythm is often identified on an ECG.
Electrode: A conductive contact that transfers electrical signals between the body and a measuring instrument. ECG electrodes detect voltage differences at the skin.
Phonocardiogram: A recording of sounds and vibrations produced by the heart and blood flow. It captures acoustic events, unlike the ECG’s electrical signals.
Willem Einthoven: A Dutch physiologist who developed the string galvanometer and established modern electrocardiography. His instruments and lead system made detailed ECG recordings practical.

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