• 15 ekg-channel-lead-electrode

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The EKG History

EKG Leads/Channels and Electrodes

An ekg is a recording of waveforms that reflects the electrical activity of the heart. The ekg lead may refer both to the number of electrodes attached to the patient and to the tracing of voltage measured between 2 electrodes or 1 electrode and another group of electrodes, which is quite confusing. Therefore, to avoid confusion, in this context ekg leads will refer to ekg channels.

EKG Leads/Channels and Electrodes

The conventional ECG records 12 leads in the following way:ekg leads or channels vs electrodes

  • Limb leads (6 limb leads with 4 electrodes)

The limb leads give information on the electrical activity of the heart from the top to the bottom and from the right to the left of the heart (frontal view). There are 4 electrodes, which are placed on the right arm, right leg (neutral), left arm and left leg and create 6 leads, included Lead I, Lead II and Lead III and aVR, aVL and aVF.

  • Chest leads (6 chest leads with 6 electrodes)

Chest leads will be created by placing 6 additional electrodes to the left side of the chest and they view the heart along the horizontal plane from front to back of the body. The chest leads are identified as V1, V2, V3, V4, V5 and V6.

ECG machines print ECG in a standardized format with 3 rows and 4 columns in the following order:

  • Column 1: Lead I, Lead II, Lead III
  • Column 2: aVR, aVL, aVF
  • Column 3: V1, V2, V3
  • Column 4: V4, V5, V6

12 channels are useful when diagnosing heart attack, but most often only Lead II, V1 and V6 are viewed. Additionally, it is very inconvenient for the patient to wear 10 electrodes for a longer period of time, therefore most portable ECG holter monitor has 7 electrodes only which can record 1, 2, 3 or 5 channels.

The ECG wave

ekg waveThe ECG reflects the electrical activity of the heart and normally it consists of a P wave, a QRS complex and a T wave. As the electrical impulse flows through the heart, a process of depolarization (action state) and repolarization (resting state) occurs. The P wave represents atrial depolarization, while the QRS represents ventricular depolarization and the T wave shows the quick repolarization of ventricles. ECG can be used to monitor the abnormalities during the depolarization and repolarization process.