Electrocardiography

Electrocardiography records the heart’s electrical activity over time using electrodes on the body. Its traces reveal the timing and pattern of cardiac depolarization and repolarization.

Cardiac action potential: A brief change in a heart cell’s membrane voltage that triggers contraction or regulates cardiac rhythm. These cellular voltage changes generate the electrical currents recorded at the body surface.
P wave: The electrocardiogram deflection produced by atrial depolarization. Its timing and shape help identify how atrial activation appears in a recording.
Electrocardiographic interpretation: The systematic analysis of electrocardiogram waveforms, intervals, and patterns. It converts recorded traces into findings about rhythm, conduction, and cardiac injury.
Vectorcardiography: A method that records the magnitude and direction of the heart’s electrical vector over time. It represents cardiac electrical activity as spatial loops rather than conventional lead traces.
Augustus Waller: A British physiologist who published one of the first human electrocardiograms in 1887. His experiments demonstrated that cardiac electrical activity could be recorded from the body surface.
Cardiac conduction system: Specialized cardiac tissue that initiates and conducts electrical impulses through the heart. Its ordered activation produces the sequence of deflections seen in an electrocardiogram.
PR interval: The electrocardiogram interval from the start of atrial depolarization to the start of ventricular depolarization. It measures conduction time from atrial activation through the atrioventricular node.
Cardiac arrhythmia: An abnormality in the rate, regularity, or site of the heartbeat’s electrical activation. Electrocardiography identifies arrhythmias by recording the timing and sequence of cardiac impulses.
Intracardiac electrogram: An electrical recording made from electrodes positioned within the heart. It measures local cardiac signals directly, unlike body-surface electrocardiography.
Willem Einthoven: A Dutch physiologist who developed the string galvanometer and standardized key electrocardiographic methods. His instruments and lead framework made clinical electrocardiography practical.

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