Leads

Question 1

Equivalent dipole theory

Answer 1

• Dipole: pair of equal electrical charge of opposite polarity separated by small distance
• Heart is a dipole: force generated has a direction and magnitude represented by a vector

o Arrowhead of vector = positive pole
o Length of arrow α magnitude

Question 2

Magnitude of vector depend on

Answer 2

 Direction of vector vs position of recording electrodes
 Distance electrode → dipole (inversely α to distance2)
 Angle of intersection btw vector and dipole axis

Question 3

Volume and linear conductor theory

Answer 3

• Thorax: volume conductor
  o Voltage of deflections differ according to position of electrodes
• Limbs: linear conductor
• Voltage constant along limb length

Question 4

Lead systems: unipolar leads

Answer 4

potential difference btw electrode on body surface and indifferent electrode
o Detect variations in electrical potential at a specific point on body surface

Question 5

Lead systems: bipolar leads

Answer 5

potential difference btw 2 recording electrodes
o Detect variations in electrical potential btw 2 points on body surface

Question 6

Deflection amplitude: max and min

Answer 6

o Maximum = vector of cardiac activation // to lead direction
o Minimum = vector of cardiac activation  to lead direction

Question 7

Deflection polarity

Answer 7

o Positive = towards positive pole
o Negative = towards negative pole

Question 8

3 anatomic planes

Answer 8

o Frontal plane → X axis = anterior/posterior
 BAILEY’S hexaxial system
o Sagittal plane → Y axis = R/L
o Horizontal plane → Z axis = superior/inferior
 Precordial/chest leads

Question 9

Bailey’s hexaxial system

Answer 9

• Frontal plane
  o Standard/classical/differential bipolar leads: leads I, II, III
   Can be represented by Einthoven’s triangle or triaxial diagram

o Augmented unipolar leads: aVR, aVL, aVF
 Indifferent electrode in – pole, exploring electrode is +
 Augmented → amplification of voltage signal by 50%

Question 10

ECG appearance in Bailey’s

Answer 10

• Normal cardiac depolarization wavefront: R → L, superior → inferior
  o + electrodes on L inferior part
   + deflections in leads I, II, aVF, III
   - deflections in leads aVL, aVR
  o Largest amplitude = lead II

Question 11

Precordial chest system

Answer 11

• Horizontal plane
  o Electrode = apex of cone
  o Epicardial surface = base of cone

Question 12

Modified Lannek’s precordial lead system

Answer 12

o 3 unipolar leads: CR6L, CR6U, CR5
o Modified: 4 exploring electrodes
 CV5RL, CV6LL, CV6LU, V10

Question 13

Takahashi’s precordial lead system

Answer 13

12 precordial leads: 6 on R, 6 on L thorax

Question 14

Modified Wilson’s chest leads

Answer 14

o Most used in vetmed
o V1 to V6

Question 15

Orthogonal bipolar lead system

Answer 15

• 3 planes: frontal, sagittal, horizontal
• X lead: frontal plane from R → L
  o Similar to lead I
• Y lead: sagittal plane from sup → inf
  o Similar to aVF
• Z lead: horizontal plane from ant → post
  o Similar to V10

Question 16

Vectocardiogram

Answer 16

• Display the various complexes in form of loops
  o Represent vectors of instantaneous mean electrical forces during cardiac cycle (3D structure)

record simultaneously 2 perpendicular leads as a loop recording
 Orientation/strength of a single cardiac dipole that best represent overall 3 cardiac planes X-Y-Z

Question 17

Time sequence/magnitude/direction of vector determined by

Answer 17

 Order of depol of atria & ventricles
 Myocardial disease state

• Direction of vector: directed toward area of > positivity

Question 18

Planar vectocardiogram

Answer 18

planar projection of 3D figure
o Body divided into 3 planes: frontal, sagittal, horizontal
o X vector: from R → L
o Y vector: from head → R leg
o Z vector: from front → back