electrocardiogram

An electrocardiogram (ECG or EKG) is a noninvasive test that records the electrical activity of the heart over time. It uses surface electrodes placed on the skin to detect tiny electrical signals generated during the cardiac cycle, producing a trace that reflects heart rhythm and conduction.

A standard twelve-lead ECG uses ten electrodes to provide twelve different perspectives on the heart’s electrical activity. Electrodes are placed on the limbs and chest, and the resulting tracings are analyzed for heart rate, rhythm, and conduction abnormalities.

The ECG trace includes specific features: the P wave corresponding to atrial depolarization; the PR interval reflecting atrioventricular conduction; the QRS complex representing ventricular depolarization; the ST segment and the T wave reflecting ventricular repolarization. Abnormalities in duration, amplitude, or morphology may indicate arrhythmias, ischemia, infarction, electrolyte disturbances, or structural or drug-related effects.

Clinical use: It is used for initial evaluation of chest pain, syncope, palpitations, and preoperative assessment, and for monitoring during surgery or critical illness. It helps diagnose arrhythmias such as atrial fibrillation, ventricular tachycardia, and conduction blocks, and can reveal signs of myocardial ischemia or previous infarction.

Interpretation requires clinical context and comparison with prior ECGs. ECGs can be affected by movement, electrode placement, skin condition, and external artifacts. They provide electrical, not mechanical, information and may be inconclusive without additional testing such as imaging or troponin measurement.

History: The method traces back to Willem Einthoven, whose string galvanometer was developed in the early 20th century, establishing the modern clinical ECG.