Electrocardiography (ECG) – Detailed Overview Definition Electrocardiography is a non-invasive diagnostic procedure that records the electrical activity of the heart over time using surface electrodes. The graphical representation obtained is called an electrocardiogram . Historical Background Late 19th century – Augustus Waller first recorded the human ECG (1887). 1903 – Willem Einthoven developed the string galvanometer and introduced the standard limb leads (Lead I, II, III), earning the Nobel Prize (1924). Since then, ECG has evolved with 12-lead systems, portable Holter monitors, and computer-assisted interpretations. Physiological Basis The heart’s rhythmic contraction is controlled by electrical impulses generated and conducted through: SA node → Atria → AV node → Bundle of His → Purkinje fibers → Ventricular muscle. Depolarization and repolarization of myocardial cells create electrical potentials detected by electrodes. ECG Leads Standa...