electrocardiograms

An electrocardiogram (ECG or EKG) is a recording of the electrical activity of the heart. Electrodes placed on the skin detect tiny electrical potentials generated with each heartbeat and transmit them to a recording device. A standard 12-lead ECG provides multiple views of the heart’s activity and is a routine tool for assessing heart rhythm, conduction, and signs of ischemia or structural problems. Recording can be done at rest or during prolonged monitoring using ambulatory devices.

The principal waveform components are the P wave (atrial depolarization), the PR interval, the QRS complex (ventricular depolarization), the ST segment, and the T wave (ventricular repolarization). Clinicians interpret the tracing by evaluating heart rate, rhythm, axis, intervals, and the morphology of waves across leads. Abnormal patterns may indicate arrhythmias such as atrial fibrillation or flutter, conduction blocks, ischemia or infarction, and electrolyte disturbances.

Indications for ECG testing include chest pain, syncope, palpitations, preoperative evaluation, and monitoring during medical or surgical treatment. Limitations include that a resting ECG represents electrical activity at a single moment and may miss intermittent problems; artifacts from movement or poor electrode contact can obscure results; and normal variants exist. When needed, additional testing such as exercise stress testing, echocardiography, or longer-term monitoring with Holter or event recorders can provide a more comprehensive assessment.

Historically, the ECG was developed in the early 20th century by Willem Einthoven, whose work laid the foundation for modern cardiac electrophysiology.