Electrocardiographic Interpretation and Abnormalities: A Comprehensive Review of Clinical, Technical, and Pathophysiological Insights

An electrocardiogram (ECG, or EKG) is a non-invasive recording of the heart’s electrical activity, captured via electrodes on the skin. Developed by Willem Einthoven in 1902, who later earned the 1924 Nobel Prize in Medicine, the ECG has become a fundamental tool in cardiac diagnostics. Physiologically, each heartbeat is driven by the coordinated depolarization and repolarization of cardiac muscle cells. The cardiac conduction system (including the sinoatrial node, atrioventricular node, bundle branches, and Purkinje fibers) orchestrates the orderly spread of electrical impulses through the atria and ventricles. The ECG tracings on paper or monitor represent the summation of these electrical currents over time, providing insight into heart rhythm, rate, and the integrity of myocardial tissue. Clinically, ECGs are prevalent in evaluating chest pain, palpitations, syncope, and numerous other cardiovascular presentations, and they are routinely used to screen for heart disease and monitor cardiac therapies. This paper provides an overview of ECG basics, interpretation of normal waveforms and intervals, and an in-depth review of various ECG abnormalities. We will discuss arrhythmias, conduction blocks, ischemic changes, electrolyte disturbances, and structural heart disease indications on ECG, describing their characteristic ECG features, clinical implications, pathophysiology, and common causes.