What is EKG:
An electrocardiogram also known as EKG or ECG is a test that records the electrical activity of the heart. A natural electrical system causes the heart muscle to contract and pump blood through the heart and out to the lungs and the rest of the body. An EKG translates the heart’s electrical activity into line tracings on paper. The spikes and dips in the line tracings are called waves.
Normal EKG tracings consist of waveform components which indicate electrical events during one heart beat. These waveforms are labeled P, Q, R, S, T and U. The following descriptions are with respect to Lead II.
- P wave is the first deflection and is normally a positive (upward) waveform. It indicates atrial depolarization.
- QRS complex follows the P wave. It normally begins with a downward deflection, Q; a larger upwards deflection, R; and then a downwards S wave. The QRS complex represents ventricular depolarization and contraction.
- T wave is normally a modest upwards waveform, representing ventricular repolarization.
- U wave indicates the recovery of the Purkinje conduction fibers. This wave component may not be observable.
Why is EKG done:
An electrocardiogram (EKG or ECG) is done to:
- Check the heart’s electrical activity.
- Find the cause of unexplained chest pain, which could be caused by a heart attack, inflammation of the sac surrounding the heart (pericarditis), or angina.
- Find the cause of symptoms of heart disease, such as shortness of breath, dizziness, fainting, or rapid, irregular heartbeats (palpitations).
- Find out if the walls of the heart chambers are too thick (hypertrophied).
- Check how well medicines are working and whether they are causing side effects that affect the heart.
- Check how well mechanical devices that are implanted in the heart, such as pacemakers, are working to control a normal heartbeat.
- Check the health of the heart when other diseases or conditions are present, such as high blood pressure, high cholesterol, cigarette smoking, diabetes, or a family history of early heart disease.
Placement of electrodes
Ten electrodes are used for a 12-lead ECG. The electrodes usually consist of a conducting gel, embedded in the middle of a self-adhesive pad onto which cables clip. Sometimes the gel also forms the adhesive. They are labeled and placed on the patient’s body as follows:
|Electrode label (in the USA)||Electrode placement|
|RA||On the right arm, avoiding thick muscle.|
|LA||In the same location where RA was placed, but on the left arm.|
|RL||On the right leg, lateral calf muscle.|
|LL||In the same location where RL was placed, but on the left leg.|
|V1||In the fourth intercostal space (between ribs 4 and 5) just to the right of the sternum (breastbone).|
|V2||In the fourth intercostal space (between ribs 4 and 5) just to the left of the sternum.|
|V3||Between leads V2 and V4.|
|V4||In the fifth intercostal space (between ribs 5 and 6) in the mid-clavicular line.|
|V5||Horizontally even with V4, in the left anterior axillary line.|
|V6||Horizontally even with V4 and V5 in the midaxillary line.|
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