• ECG Electrodes
• Limb Electrodes
• Chest Electrodes
• Placement of Chest Electrodes
• Voltmeter and ECG
• 3 Limb Electrodes
• Principle of Lead I
• Einthoven's Triangle
• Electrical Axis of ECG Lead
• Wilson Central Terminal (WCT)
• Einthoven ECG Leads
• Goldberger ECG Leads
• Hexaxial System
• Chest Electrodes
• 12-Lead ECG
• ECG Leads in 3D Space
• Ventricular Vectors
• ECG and Ventricular Vectors
• CG Leads and 12-Lead ECG
• Chest Leads (V1-V2)

ECG Electrodes

• The ECG device has 10 electrodes that are applied on the body
• Limb electrodes (4)
• Attached to the limbs
• The black limb electrode is the ground
• Chest electrodes (6)
• Applied to the chest
• The electrodes record the electrical vector of the myocardium
• The ECG device displays the vector as an ECG waveform
• The ECG paper has 12 leads:
• V1, V2, V3, V4, V5, V6
• I, II, III, aVF, aVL, aVR

Chest Electrodes

• Chest electrodes are suctioned onto the chest
• Placement is important
  
  
• Electrode placement
• V1 - 4th intercostal space, right sternal border
• V2 - 4th intercostal space, left sternal border
• V3 - Exactly between V2 and V4
• V4 - 5th intercostal space, midclavicular line
• V5 - 5th intercostal space, anterior axillary line
• V6 - 5th intercostal space, midaxillary line
  
  
• Chest electrodes appear on the ECG paper as:
• Chest leads (V1-V6)

Voltmeter and ECG

Simple ECG Device

• An ECG device is a voltmeter that records volts as an ECG curve
• Volts are generated during the propagation of the electrical vector through the myocardium
• The voltmeter (ECG) always has one electrode positive and the other negative
• If there is a depolarized (-) and repolarized (+) part of the myocardium between the electrodes (electrical vector)
• Then the voltmeter measures the electric voltage, which the ECG displays as spikes or waves
• If there is only a depolarized (-) or only a repolarized (+) part of the myocardium between the electrodes
• Then the voltmeter does not measure any electric voltage, which the ECG displays as an isoelectric line

Principle of Lead I

Lead I

• 3 limb electrodes are placed on the wrists and left ankle
• The body is a good electrical conductor, so it doesn't matter if you place the electrode
• on the shoulder or on the wrist
• on the thigh or on the ankle
• The picture shows Lead I
• Negative electrode on the right shoulder
• Positive electrode on the left shoulder

Electrical Axis of ECG Lead

• Each bipolar ECG lead (I, II, III) has
• a positive (+) and a negative (-) electrode
• an electrical axis between the (+) and (-) electrodes
  
  
• The heart's electrical vector
• projects onto the electrical axis of the ECG lead
  
  
• Parallel shifting of the ECG lead (I, II, III)
• does not change the vector magnitude on the electrical axis

Einthoven ECG Leads

• Electrodes are placed on the patient's body (there are 10 of them)
• On the ECG paper, we see ECG leads (there are 12 of them) generated by the ECG device from the placed electrodes

Einthoven ECG Leads

• Leads (I, II, III) can be shifted in parallel towards the central terminal
• The Wilson central terminal serves as a negative electrode calculated by the ECG device
• The electrical axis of each lead (I, II, III)
• directs from the terminal towards the positive electrode

Hexaxial System

• From 3 electrodes placed on the limbs
• The ECG device generates 6 ECG leads
• Einthoven leads (I, II, III)
• Goldberger leads (aVR, aVF, aVL)
• The leads (I, II, III, aVR, aVF, aVL) together are referred to as limb leads
  
  

Hexaxial System

• Created by combining Einthoven and Goldberger leads
• From central terminal, 6 ECG leads are oriented
• Each ECG lead "views" the heart from a different angle of perspective
• These 6 ECG leads are sometimes referred to as the hexaxial system
• Limb leads "view" the heart in the frontal plane
• They record the electrical heart vector

12-Lead ECG

• The ECG device has 10 electrodes that are attached to the body
• The black electrode serves as ground and does not contribute to generating the ECG waveform
• Thus, the ECG device uses 9 electrodes for generating the ECG waveform
  
  
• The ECG paper displays 12 leads, which the ECG device generates from the attached electrodes
  
  
• Standard limb leads (I, II, III, aVR, aVF, aVL):
• Einthoven's leads (I, II, III)
• These are bipolar because they are derived from a positive and a negative electrode
• Goldberger's leads (aVR, aVF, aVL)
• These are unipolar because they are derived only from a positive electrode (and the central terminal)
  
  
• Wilson's chest leads (V1-V6)
• These are unipolar because they are derived only from chest electrodes (and the central terminal)

Ventricular Vectors

• The thin ventricular septum is first activated
• Resulting in a small septal vector (V_S)
• Q wave
• Then the massive left ventricle is activated
• Resulting in a large main vector (V_M)
• Simultaneously, the thin right ventricle is also activated
• Small right ventricular vector
• does not influence the direction of the main vector
• R wave
• Finally, the base of the left ventricle is activated
• Resulting in a small terminal vector (V_T)
• S wave
  
  
• You must imagine the vectors in 3D space
• ECG leads record vectors over time

Sinus Rhythm

• On the ECG is a sinus rhythm
• Note how the height of the QRS complexes changes in the different leads
• Vectors in the atria create the P wave
• Vectors in the ventricles create the QRS complex and the T wave

Chest Leads (V1-V2)

• Chest leads (V1-V2) are placed parasternally in the 4th intercostal space
• Physiological P wave (V1-V2) is equiphase (positive-negative)
• Leads (V1-V2) are used for differential diagnosis:
• Left Anterior Hemiblock vs. Old Anteroseptal Infarction

Differential Diagnosis with V1-V2

• Correct placement of electrodes V1-V2 in the 4th intercostal space
• P wave is equiphase
• Sometimes in V1-V2 a QS configuration is observed, which may indicate:
• Left Anterior Hemiblock, or Old Anteroseptal Infarction
• If V1-V2 is placed lower (6th intercostal space)
• P wave is monophasic positive
• rS configuration (V1-V2) appears
• This indicates a Left Anterior Hemiblock
• Old infarction would still show a QS configuration (without r wave)
• If V1-V2 is placed higher (2nd intercostal space)
• P wave is monophasic negative