The Electrocardiogram (ECG)
An electrocardiogram, also referred to as an ECG or EKG (older term) is a graphical representation of the electrical avtivity in the heart or how the heart reacts when it is stimulated.
An ECG is performed by placing electrodes, or sensors, on specific places on the body in a specific configuration. These electrodes are attached to lead wires. The lead wires are then attached to a recorder. Together, the electrode and the corresponding lead wire are called a “Lead.”
A standard electrocardiogram consists of three leads. These are designated by the roman numerals – I, II, III. These leads are called the primary leads. A standard ECG gives basic information as to heart rate and rhythm.
When more information is needed, clinicians turn next to a diagnostic ECG or twelve lead ECG. The twelve lead ECG consists of three primary leads (I, II, III); three augmented leads (AVR, AVL, AVF.) Augmented leads are the electrical mirror image of the primary leads. Finally, there are five chest leads (Designated v1-v5) that are placed on the left side of the chest.
All leads measure electrical activity in different places in the heart. The signals represent the flow of electricity (in the form of electrons) from a region of negative charge to a region of positive charge. As this electrical charge progresses, it generates an image of the progression of a heart beat and its relationship to previous heartbeats and those that follow.
When all leads are measured together, the result is a three-demensional, electrical profile of the heart.
An ECG is a tool clinicians use to evaluate heart function with respect to heart rate (how fast or how slow the heart beats), rhythm (whether heart rate is regular or irregular), infarction (tissue death) or impending infarction, hypertrophy (enlarged heart), or axis deviations (the heart beat follows a differnt path, usually as the result of an infarction.
The electrocardiogram is truly a useful tool in medical science.
