12lead

12-lead electrocardiography, commonly referred to as a 12-lead ECG, is a noninvasive test that records the heart's electrical activity from 12 perspectives to produce a concise representation of cardiac electrophysiology. A standard 12-lead setup uses 10 electrodes: four limb electrodes (right arm, left arm, left leg, right leg) and six precordial chest electrodes (V1–V6). These yield the three standard limb leads I, II, III; the three augmented leads aVR, aVL, aVF; and the six chest leads V1–V6. The limb leads form the frontal plane (Einthoven triangle) and the chest leads provide a horizontal plane view.

The recording is performed with the patient at rest or during exercise; the tracing typically lasts about 10 seconds. Clinicians interpret patterns of P waves, QRS complexes, ST segments, and T waves to assess rhythm, conduction, chamber size, electrolyte effects, ischemia, and infarction. The 12 leads collectively help localize ischemia or infarction in the heart and detect arrhythmias, ventricular hypertrophy, and signs of previous myocardial injury. Interpretation requires clinical context, and artifacts from movement, poor electrode contact, or improper placement can affect accuracy.

History and limitations: the 12-lead system evolved from the work of Willem Einthoven and became standardized in the mid-20th century. While widely used, it provides only a brief snapshot and may miss transient events; it is often complemented by continuous monitoring and additional tests. Safety is high; the procedure is noninvasive and brief, though skin irritation from electrodes can occur.