Depolarization Dynamics and Dipole Generation The ECG visualizes the heart’s electrical activity as cells transition from a negatively charged rest state to a positively charged depolarized state, creating a dipole with a vector pointing toward the positive charge. The magnitude of this dipole corresponds directly to the size of the deflection observed on the tracing. When the depolarization wave is aligned toward an electrode, a positive deflection occurs, and when it moves away, a negative deflection is produced. In moments without charge differences, no dipole forms, resulting in an isoelectric line.
Electrode Configurations and Vector Projections The system uses 10 electrodes—four on the limbs and six on the chest—to construct a 12-lead view of the heart’s electrical activity. Limb leads include both bipolar and augmented unipolar configurations that capture electrical vectors oriented at specific angles. The electrodes register only the component of the heart’s electrical vector that is parallel to them, with the perpendicular component having no effect on the deflection. This alignment explains why the same depolarization wave can produce varying tracings in different leads.
Regional Cardiac Assessment via Multi-Lead Perspectives The placement of leads provides distinct views of the heart, each corresponding to a specific anatomical region. Inferior leads (II, III, aVF), lateral leads (I, aVL, V5, V6), septal leads (V1, V2), and anterior leads (V3, V4) are strategically arranged to reflect electrical activity from regions supplied by different coronary arteries. This multi-lead approach enables targeted diagnostic insights by correlating changes in the deflection patterns with particular cardiac areas. The 12-lead system thus offers a comprehensive map of the heart’s structure and function.