Basic Electrocardiogram And Electrode Placement
Electrocardiography is the process of producing an electrocardiogram (ECG or EKG). It is a graph of voltage versus time of the electrical activity of the heart using electrodes placed on the skin. Electrocardiogram (EKG), introduced into clinical practice more than 100 years ago by Einthoven, is a recording of the heart’s electrical lines, activity occurring sequentially over time. Atrial depolarization waves (P waves), ventricular depolarization waves (QRS complex) and ventricular repolarization waves (T waves) are recorded sequentially for each cardiac cycle.
The sequence is always P – QRS – T. ECG curve recorded from the electrode facing the left ventricle.
Before Using Electrocardiogram (ECG) Notes:
- An ECG is a series of waves and deflections that record the electrical activity of the heart from a specific “view.”
- Many views, each called a cable, monitor the change in voltage between electrodes positioned at different positions on the body.
- Leads I, II, and III are bipolar leads, which consist of two electrodes of opposite polarity (positive and negative). The third electrode (ground) minimizes electrical activity from other sources.
- The aVR, aVL, and aVF leads are unipolar and consist of one positive electrode and a reference point (with zero electric potential) located at the center of the heart’s electric field.
- Leads V1 – V6 are unipolar leads and consist of one positive electrode with a negative reference point located at the heart’s electrical center.
- The change in voltage is amplified and displayed visually on an oscilloscope and graph paper.
- The ECG tracing looks different for each lead as the angle of the electrical activity recording changes with each lead.
- Several different angles allow for a more accurate perspective than one point of view.
- The ECG machine can be set to make the skin electrodes positive or negative. The polarity depends on which cable the machine is taping on.
- The cord that is attached to the patient is divided into wires of different colors: three, four, or five for monitoring purposes, or ten for a 12 lead ECG.
- Incorrect electrode placement can turn ECG tracking abnormal.
Standard Limb Lead Electrode Placement
Standard Limb Leads ECG
Augmented Limb Leads
Standard Chest Lead Electrode Placement
Electrode Placement Using a 3 or 5 Wire Cable
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Sumber dari buku ECG Note by Shirley A. Jones, MS Ed, MHA, EMT-P