twelvelead

A twelve-lead electrocardiogram (12-lead ECG) is a noninvasive diagnostic test that records the heart's electrical activity from twelve distinct viewpoints. The recording uses ten surface electrodes placed on the limbs and chest to produce twelve standard leads, providing a comprehensive view of cardiac conduction and rhythm.

Lead configuration and electrode placement: Three limb electrodes are placed on the arms and legs to form the frontal plane leads, with a fourth limb electrode serving as a ground. The six chest (precordial) leads, V1 through V6, are placed on the chest at specified intercostal spaces and positions to view the heart in the horizontal plane. The standard limb leads I, II, and III originate from the limb electrodes (bipolar) and form Einthoven’s triangle, while the augmented limb leads aVR, aVL, and aVF provide additional frontal-plane views.

Clinical uses: The 12-lead ECG is used to detect myocardial ischemia or infarction, arrhythmias, conduction abnormalities (such as AV block), chamber hypertrophy, and electrolyte disturbances. It is routinely employed in chest-pain assessment, preoperative evaluation, and monitoring in critical care. The twelve views help localize problems within the heart and guide urgent management; serial ECGs can track changes over time.

Limitations and interpretation: Accurate interpretation depends on correct electrode placement and patient factors. Artifacts from movement, improper skin preparation, or instrumentation can affect results. Some conditions may be occult on ECG, requiring additional testing or imaging for definitive diagnosis. Standardized interpretation guides and clinician expertise are essential for accurate diagnosis.