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    Electrocardiogram (EKG) Components and Intervals

    Electrocardiogram (EKG) Components and Intervals

    Picture of the intervals and components of an EKG (electrocardiogram)

    An electrocardiogram (EKG, ECG) is a test that measures the electrical signals that control heart rhythm. The test measures how electrical impulses move through the heart muscle as it contracts and relaxes.

    The electrocardiogram translates the heart's electrical activity into line tracings on paper. The spikes and dips in the line tracings are called waves.

    • The P wave is a record of the electrical activity through the upper heart chambers (atria).
    • The QRS complex is a record of the movement of electrical impulses through the lower heart chambers (ventricles).
    • The ST segment shows when the ventricle is contracting but no electricity is flowing through it. The ST segment usually appears as a straight, level line between the QRS complex and the T wave.
    • The T wave shows when the lower heart chambers are resetting electrically and preparing for their next muscle contraction.
    By Healthwise Staff
    Primary Medical Reviewer Rakesh K. Pai, MD, FACC - Cardiology, Electrophysiology
    Specialist Medical Reviewer George Philippides, MD - Cardiology
    Last Revised March 7, 2012

    Last Revised: March 7, 2012

    Author: Healthwise Staff

    Medical Review: Rakesh K. Pai, MD, FACC - Cardiology, Electrophysiology & George Philippides, MD - Cardiology

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