1. Practical Electrocardiography Introduction
Scott Ewing, D.O.
Cardiology Fellow
August 2, 2006

2. Syllabus Introduction Axis Determination
Atrial Arrhythmias, Bradycardias, and AV Conduction Block
Junctional and Broad Complex Tachycardias
Myocardial Ischemia and Acute Myocardial Infarction
Conditions Affecting the Left Side of the Heart
Conditions Affecting the Right Side of the Heart
Conditions Not Primarily Affecting the Heart
Exercise Tolerance Testing

3. Introduction Anatomy EKG Paper Lead Placement Normal EKG
Axis Determination

8. His-Purkinje Conduction System

10. The EKG Paper
Time intervals indicated for the thick and thin vertical grid lines on the EKG paper are appropriate for the standard paper speed of 25 mm/sec
Amplitudes indicated for the thick and thin horizontal grid lines are appropriate for the standard gain of 10 mm/mV
Each small square is therefore 0.04 s × 0.1 mV, and each large square is 0.20 s × 0.5 mV

11. Depolarization

12. Normal EKG

14. EKG Limb Leads

15. EKG Limb Leads

16. Willem Einthoven (1860 – 1927) Dutch doctor and physiologist
Invented the first practical electrocardiogram in 1903
Nobel Prize Medicine in 1924
Died in Leiden in the Netherlands and is buried in the graveyard of the Reformed Church at 6 Haarlemmerstraatweg in Oegstgeest

18. EKG Augmented Limb Leads

19. EKG Frontal Plane

20. EKG Frontal Plane

23. EKG Precordial Leads

27. Normal Findings Tall R waves Prominent U waves
ST segment elevation (high­take off, benign early repolarization)
Exaggerated sinus arrhythmia
Sinus bradycardia
Wandering atrial pacemaker
Wenckebach phenomenon
Junctional rhythm
1st degree heart block

28. Waveform Review

29. P Wave

30. P Wave

31. P Wave Atrial activation begins in the SA node Normal amplitude
Spreads in radial fashion to depolarize the right atrium, interatrial septum, then the left atrium
Last area of the left atrium to be activated is the tip of the left atrial appendage
Normal amplitude
Seldom exceeds 0.25 mV normally in limb leads
In precordial leads, positive component is normally less than 0.15 mV

32. P Wave Characteristics
Positive in leads I and II
Best seen in leads II and V1
Commonly biphasic in lead V1
< 3 small squares in duration
< 2.5 small squares in amplitude

33. P Wave – Lead II

34. P Wave – Lead V1

35. PR Interval / Segment

36. P Wave

37. PR Interval Beginning of P wave to beginning of QRS complex
Interval between the onset of atrial depolarization and onset of ventricular depolarization
Time required for the activation impulse to advance from atria through the AV node, bundle of His, bundle branches, and the Purkinje fibers until ventricular myocardium begins to depolarize
Does not include duration of conduction from SA node proper to the right atrium

38. PR Interval / Segment

39. PR Interval Normal PR Interval 0.12-0.20 seconds (adults)
Shorter in children, longer in older persons
May become shorter as sinus rate increases
Should be taken from lead with the largest and widest P wave and longest QRS duration
Such selection avoids inaccuracies incurred by using leads in which the early part of the P wave or QRS complex is isoelectric

40. PR Interval
Most of the AV conduction time is consumed by impulse conduction proximal to the His bundle
Normal AH interval= ms
Normal HV interval= ms
Longer AH interval is result of slower conduction through AV node

41. PR Segment
Horizontal line between the end of the P wave and the beginning of the QRS complex
Duration depends on the duration of the P wave as well as the impulse conduction through the AV junction
Usually isoelectric, however it is often displaced in a direction opposite to the polarity of the P wave
Depressed in most of the conventional leads except aVR
Displacement is mainly due to atrial repolarization

42. PR Interval – Lead II

43. QRS Complex

44. QRS Complex

45. QRS Complex Q wave – Any initial negative deflection
R wave – Any positive deflection
S wave – Any negative deflection after an R wave

46. QRS Complex

47. QRS Complex
Resultant electrical forces generated from ventricular depolarization
Begins at the middle third of the left interventricular septal surface
Spreads in a rightward direction
Right ventricle begins to depolarize shortly after the initiation of left ventricular activation

48. Ventricular Depolarization

49. QRS Complex
Soon after septal activation, the impulse arrives at most of the subendocardial layer of the myocardium of the apical and free wall of both ventricles through the Perkinje network and spreads in all directions
Impulse spreads in endocardial to epicardial direction

50. QRS Complex
Basal portion of septum and the posterobasal portion of the free wall of the LV are last areas of depolarization
LV contributes most of the QRS forces due to larger muscle mass
Polarity and amplitude of the QRS complex in the various leads are determined by the relation between these vectors and the lead axes

52. QRS Complex QRS duration represents duration of ventricular activation
Should be measured from lead with widest QRS complex
Traditionally measured from the limb leads, but V1 or V2 may have the widest complex
Normal QRS varies between second

53. QRS Complex
Morphology and amplitude are affected by constitutional variables
Advancing age: amplitude decreases
Men > women
Blacks > whites
Thin > obese
In limb leads, morphology depends on the orientation and amplitude of the QRS vectors in the frontal plane

54. QRS Complex Lead I: usually records a dominant R wave
In younger subjects with more rightward axis, R/S ratio < 1 may be seen
Lead II: invariably has prominent R wave since mean vector is always toward II if QRS axis is normal
Lead aVR: always records negative deflection
Lead III: variable – Why?

55. Intrinsicoid Deflection
Represents the moment when the epicardial muscle lying under the electrode becomes depolarized
Beginning of the abrupt downstroke after the R wave reaches its peak
Time of onset measured from beginning of QRS to point of abrupt downstroke
Used mostly in diagnosis of ventricular hypertrophy and BBB when onset is delayed

56. QRS Complex – Lead V3

57. ST Segment

58. ST Segment
Segment between end of QRS complex (J point or ST junction) and beginning of the T wave
Represents a state of unchanged polarization between the end of depolarization and the beginning of repolarization
Stage when terminal depolarization and starting repolarization are superimposed and cancel each other

59. ST Segment
Most important information regarding ST segment is presence or absence and degree of displacement from isoelectric line
TP segment is used as reference baseline
Limb leads – elevation or depression < 1mm
Precordial leads- elevation sometimes seen and normal in V2-V3 (< 2mm), rarely > 1mm in V5-V6
Any ST depression in precordial leads is abnormal (normal vector in horizontal plane is anterior and leftward)

60. ST Segment – Lead aVF

61. T Wave

62. T Wave Represents potential for ventricular repolarization
Proceeds in general direction of ventricular excitation
Polarity of resultant T wave is similar to that of the QRS vector
Upright in I, II, V5-V6
Inverted in aVR
When inverted in 2 or more of right precordial leads, referred to as persistent juvenile pattern

63. T Wave Limb leads Precordial leads: Tallest in lead II
Normally < 6mm in all limb leads
Should never be < 0.5mm
Precordial leads:
Tallest in V2-V3 (average 6mm)
Smaller in left precordial leads

64. T Wave Normally asymmetrical
First half has more gradual slope than second half
First portion has upward concavity if T-wave is upright and downward concavity if T-wave is inverted
In right precordial leads, if T-wave is biphasic, the first portion is upright and second portion inverted
Negative-positive biphasic T-wave is abnormal in leads V1-V3

65. T Wave – Lead aVF

66. QT Interval

67. QT Interval Represents duration of ventricular electrical systole
Measured from beginning of QRS complex to end of the T wave
Lead with a large T wave and distinct termination is used
Leads V2-V3 are usually best for this specific measurement

68. QT Interval Varies with heart rate (see table)
Lengthens as heart rate decreases
Shortens as heart rate increases
Increases slightly with age
Diurnal variation of QTI has been documented
Longer during sleep than during waking hours

69. Normal Limits QT Interval

70. QT Interval Normal = 0.35 – 0.45 second for HR=70 Bazett's correction
For every 10-beat increase or decrease of the rate, 0.02 second is deducted or added to the QTI
Bazett's correction
QTc = measured QTI divided by square root of RR interval
Obvious abnormality if QTI > ½ RR interval

71. QT Interval – Lead aVF

72. U Wave

73. U wave Small, low-frequency deflection that appears after the T wave
Genesis is controversial
Afterpotentials of ventricular myocardium
Repolarization of the Perkinje fibers
Amplitude is proportional to T wave
Usually 5-25% of T wave voltage
Largest in leads V2-V3
Prominent during slower heart rates
Initial portion is normally steeper than terminal portion

74. Conclusion
Questions?