Basics of 12 Lead ECG's Vector

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Basics of 12 Lead ECG'sVector

• There are three basic "laws" of
  Electrocardiography.
• These "laws" have to do with the direction of
  flow of electrical conduction in the heart or
  what we term as vector.

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Basics of 12 Lead ECG'sVector

• 1. Movement of the electrical impulse
  towards the positive electrode will result in a
  positive deflection on the ECG.
•  
•  
• -
•  

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Basics of 12 Lead ECG'sVector

• 2. Movement of the electrical impulse toward the
  negative electrode will result in a negative
  deflection on the ECG.
• -
  

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Basics of 12 Lead ECG'sVector

• 3. Movement of an electrical impulse
  perpendicular to a line between the positive and
  negative electrodes results in a bi-phasic (part
  upright and part downward) deflection on the ECG.
•   -

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Basics of 12 Lead ECG'sVector

• By understanding this concept of vector and
  knowing the "normal" vector of each of the 12
  leads of the 12 lead ECG it becomes quite easy to
  identify problems in the direction of
  depolarization. It is also from this knowledge
  that one identifies the Mean QRS Axis. Using the
  six limb leads we identify the axis in relation
  to what is known as the frontal plane. Two major
  factors help to determine this mean QRS Axis,
  they are
•  
• The anatomical position of the heart
• The direction of ventricular depolarization.

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Basics of 12 Lead ECG'sDetermining AXIS

• Technique 1 Two Lead Method or Quadrant Method
• This method uses just two leads of the six limb
  leads and works well in critical situations to
  get a general idea of the Mean Axis of the QRS.
  We will look at Lead 1 and at Lead AVF for this
  technique.

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Basics of 12 Lead ECG's Determining AXIS

• 1. Leads 1 and AVF divide
• the thorax into quadrants,
• (Left, Normal, Right, No Man's)
•  
• 2. If leads 1 and AVF are both upright then the
  Axis is normal.
•  
• 3. If lead 1 is upright and lead AVF is downward
  the Axis is Left.

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Basics of 12 Lead ECG's Determining AXIS

• 4. If lead AVF is upright and lead 1 is downward
  then the Axis is Right
• 5. If both leads are downward then the Axis is
  extreme Right Shoulder and most often is Vent.
  Tachy

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Basics of 12 Lead ECG's Determining AXIS

• Method 2 Three Lead technique
•  
• This method uses the three limb leads I, II, III
  to determine the axis of the QRS.

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Basics of 12 Lead ECG's Determining AXIS

• Method 3 Using the Hexaxial Diagram to find
  the degree of Axis Deviation
• This technique is a little hard to learn
• but it is also the most accurate( or 100 to
  150)

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Basics of 12 Lead ECG's Determining AXIS

• To determine the axis a scale must be used such
  as the one at the left.

-30 to 120
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Basics of 12 Lead ECG's Determining AXIS

• First you must find the most equiphasic QRS
  complex in the six limb leads. This is done by
  adding and subtracting the number of squares each
  QRS complex has above the baseline and below the
  baseline in each lead.

-30 to 120
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Basics of 12 Lead ECG's Determining AXIS

• The axis will be
• perpendicular (right
• angle) to this lead.
• If the perpendicular
• lead has a positive QRS,
• orient the axis to the
• positive pole of this lead.
• If it is negative then
• orient it to the negative
• pole.
•  

-30 to 120
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Basics of 12 Lead ECG'sCauses of Abnormal Axis

• Left Axis Deviation An axis between -30 and
  -90
•  
• May be normal in the elderly and very obese
• Due to high diaphragm during pregnancy, ascites,
  or ABD tumors
• Left Anterior Hemiblock
• Left Bundle Branch Block
• WPW Syndrome
• Congenital Lesions
• Right Vent. Pacer or ectopic rhythms
• Emphysema

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Basics of 12 Lead ECG's Causes of Abnormal Axis

• Right Axis Deviation An axis between 120 and
  180
•  
• Can be normal variant
• Right Vent. Hypertrophy
• Right Bundle Branch Block
• Left Posterior Hemiblock
• Left Ventricular ectopic rhythms
• Some right Vent. Ectopic rhythms
• WPW Syndrome

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Basics of 12 Lead ECG's Causes of Abnormal Axis

• Extreme Right Axis Deviation An axis between
  -90 and 180
•  
• Ventricular ectopic rhythms
• Right Vent. Paced rhythms
• Less commonly seen in patients with
  cardiomyopathies and in those with multiple MI's