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CORN 201: Introduction to 12   Lead ECGs and Axis        Sylvia van Eijk        Humber College
What information can a 12 lead ECG                provide?•   Ischemic events•   MIs•   Bundle branch blocks•   Anterior a...
When should we do a 12 lead ECG?•   Analyze a cardiac rhythm•   Patient symptoms: e.g. chest pain, SOB•   Suspected MI•   ...
Einthoven’s ECG machine
12 lead ECG• Electrical recording of the heart• Conduction system creates electrical  impulses• Majority of cells in the b...
Normal 12 lead ECG
Electrical forces and vectorsCardiac vector:• Vector describes electrical impulses of cells• Electrical current is generat...
Cardiac Vector
Cardiac Vectors• Add up when going in the same direction• Cancel each other out if going in opposite  directions• Sum of a...
Cardiac Vectors
12 lead ECG leadsSix limb leads:• 3 standard limb leads: I, II, and III• 3 augmented leads: aVR, aVL, and aVFSix precordia...
12 lead ECG leadsPositive electrode:• Attached to extremities or designated areas  of chestNegative electrode:• Single ele...
12 lead ECG leads• Standard limb leads are bipolar• Positive and negative electrodes are  attached to the extremities• Det...
Standard limb leads
Lead I
Lead II
Lead III
Augmented limb leads• Unipolar• aVR, aVL, aVF• Positive electrode on one of three  extremities• Negative electrode: centra...
Augmented leads and axes
Lead Axis• Each lead measures the difference in  electrical potential between the positive and  negative electrodes (or CT...
Lead Axis
Frontal and Horizontal Planes• 3 standard limb leads and 3 augmented  leads measure electrical activity of the heart  in t...
Frontal and horizontal planes
Einthoven’s Triangle
Einthoven’s Law• Lead I + Lead III = Lead II
Triaxial reference figure for leads I, II, III
Triaxial reference figure for augmented leads
Hexaxial reference figure• Combines the triaxial reference figures for  the standard and augmented limb leads
Precordial leadsSix unipolar leads:• V1,V2, V3, V4, V5, V6• Use positive electrode and central terminal
Precordial lead placement
Right sided chest leads
Precordial lead axes
The heart in 3 dimensions
Facing Leads
Review QuestionsA ________ lead represents the difference in  electrical potential between 2 electrodes:• Unipolar• Bipola...
Review questionsThe placement of the V4 positive chest  electrode is:A. Left side of the sternum in the 4th ICSB. Midclavi...
Review questionsThe ____________ surface of the heart is  viewed by ECG leads II, III, and aVF.A. LateralB. AnteriorC. Inf...
Cardiac vectors and the QRS axis
QRS axisPoints to remember:• QRS axis points to the left and downward• QRS axis most important• P and T axis rarely determ...
Currents, vectors, and axes• Parallel to lead axis → positive or negative  deflection• Perpendicular to lead axis → no def...
Direction of flow of electrical currents
Hexaxial reference figure• Identify direction of the QRS axis• Use the 6 limb lead axes• Spaced 30 degrees apart around th...
Hexaxial reference figure
Normal and abnormal QRS axes
Causes of abnormal axis•   Ventricular enlargement•   Ventricular hypertrophy•   Bundle branch block•   Fascicular block
Left axis deviationDisorders that may lead to LAD:• Systemic hypertension, aortic stenosis• Ischemic heart disease• Other ...
Right axis deviation• COPD, PE, congenital heart disease• Other disorders that cause severe  pulmonary hypertension• RBBB•...
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  1. 1. CORN 201: Introduction to 12 Lead ECGs and Axis Sylvia van Eijk Humber College
  2. 2. What information can a 12 lead ECG provide?• Ischemic events• MIs• Bundle branch blocks• Anterior and posterior fascicular blocks• Axis determination• Hypertrophy• Ectopy vs abberrancy
  3. 3. When should we do a 12 lead ECG?• Analyze a cardiac rhythm• Patient symptoms: e.g. chest pain, SOB• Suspected MI• Electrolyte imbalances• Digoxin Toxicity
  4. 4. Einthoven’s ECG machine
  5. 5. 12 lead ECG• Electrical recording of the heart• Conduction system creates electrical impulses• Majority of cells in the body generate an electrical signal that can be measured
  6. 6. Normal 12 lead ECG
  7. 7. Electrical forces and vectorsCardiac vector:• Vector describes electrical impulses of cells• Electrical current is generated by depolarization and repolarization• Vectors show strength and direction of the electrical impulse• Depicted as an arrow
  8. 8. Cardiac Vector
  9. 9. Cardiac Vectors• Add up when going in the same direction• Cancel each other out if going in opposite directions• Sum of all vectors in ventricle = electrical axis• Determination of QRS vector
  10. 10. Cardiac Vectors
  11. 11. 12 lead ECG leadsSix limb leads:• 3 standard limb leads: I, II, and III• 3 augmented leads: aVR, aVL, and aVFSix precordial leads: V 1-6• 15 lead ECG: V7-9
  12. 12. 12 lead ECG leadsPositive electrode:• Attached to extremities or designated areas of chestNegative electrode:• Single electrode attached to an extremity or an ‘indifferent’ zero reference point – the central terminal
  13. 13. 12 lead ECG leads• Standard limb leads are bipolar• Positive and negative electrodes are attached to the extremities• Detect electrical activity between 2 electrodes
  14. 14. Standard limb leads
  15. 15. Lead I
  16. 16. Lead II
  17. 17. Lead III
  18. 18. Augmented limb leads• Unipolar• aVR, aVL, aVF• Positive electrode on one of three extremities• Negative electrode: central terminal
  19. 19. Augmented leads and axes
  20. 20. Lead Axis• Each lead measures the difference in electrical potential between the positive and negative electrodes (or CT)• Hypothetical line joining the poles of a lead is the ‘axis’ of the lead (vector)
  21. 21. Lead Axis
  22. 22. Frontal and Horizontal Planes• 3 standard limb leads and 3 augmented leads measure electrical activity of the heart in the 2-dimensional frontal plane
  23. 23. Frontal and horizontal planes
  24. 24. Einthoven’s Triangle
  25. 25. Einthoven’s Law• Lead I + Lead III = Lead II
  26. 26. Triaxial reference figure for leads I, II, III
  27. 27. Triaxial reference figure for augmented leads
  28. 28. Hexaxial reference figure• Combines the triaxial reference figures for the standard and augmented limb leads
  29. 29. Precordial leadsSix unipolar leads:• V1,V2, V3, V4, V5, V6• Use positive electrode and central terminal
  30. 30. Precordial lead placement
  31. 31. Right sided chest leads
  32. 32. Precordial lead axes
  33. 33. The heart in 3 dimensions
  34. 34. Facing Leads
  35. 35. Review QuestionsA ________ lead represents the difference in electrical potential between 2 electrodes:• Unipolar• Bipolar• Central• Terminal
  36. 36. Review questionsThe placement of the V4 positive chest electrode is:A. Left side of the sternum in the 4th ICSB. Midclavicular line in the 5th ICSC. Anterior axillary line at the 5th ICSD. Midaxillary line at the 6th ICS
  37. 37. Review questionsThe ____________ surface of the heart is viewed by ECG leads II, III, and aVF.A. LateralB. AnteriorC. InferiorD. Posterior
  38. 38. Cardiac vectors and the QRS axis
  39. 39. QRS axisPoints to remember:• QRS axis points to the left and downward• QRS axis most important• P and T axis rarely determined
  40. 40. Currents, vectors, and axes• Parallel to lead axis → positive or negative deflection• Perpendicular to lead axis → no deflection• The greater the magnitude, the larger the deflection
  41. 41. Direction of flow of electrical currents
  42. 42. Hexaxial reference figure• Identify direction of the QRS axis• Use the 6 limb lead axes• Spaced 30 degrees apart around the wheel: 0 to 180°• Divided into 4 quadrants
  43. 43. Hexaxial reference figure
  44. 44. Normal and abnormal QRS axes
  45. 45. Causes of abnormal axis• Ventricular enlargement• Ventricular hypertrophy• Bundle branch block• Fascicular block
  46. 46. Left axis deviationDisorders that may lead to LAD:• Systemic hypertension, aortic stenosis• Ischemic heart disease• Other disorders affecting LV• PVCs and VT of RV origin• Late inferior MI
  47. 47. Right axis deviation• COPD, PE, congenital heart disease• Other disorders that cause severe pulmonary hypertension• RBBB• Normal in infants and young adults (up to 120°)

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