1. LU6 Enhancement Lectures PGH IM Residents 2011

2. This slide shows the conduction system of the heart
This slide shows the conduction system of the heart. First the SA node located at the postero-superior part of the right atrium. It is the heart’s predominant pacemaker. Each depolarization wave proceeds outwards from the SA node and stimulates both atria to contract. Then the AV node, where the depolarization slows down, then it reaches the ventricular conduction system, beginning at the His bundle. Thereafter, conduction proceeds very rapidly to the right and left bundle branches. The terminal filaments of the Purkinje fibers spread out just beneath the endocardium lining both ventricles, and proceeding towards the outside surface.

3. Generation of action potential
This shows the correlation of the ECG tracing with the action potential, most specifically the ventricular contraction with the action potential. The QRS complex corresponds to the upward stroke at phase 0 to 1. Then at the end of phase 1 to phase 2 (the plateau) until the beginning of phase 3 corresponds with the ST segment; and the T wave with the rapid phase of repolarization.
Generation of action potential

4. The ECG is recorded in a long strip of ruled paper
The ECG is recorded in a long strip of ruled paper. The smallest subdivisions are 1 mm long and 1mm high. Between the heavy black lines are 5 small squares. Each small square is equivalent to 0.04 seconds horizontally and 1 millivolt vertically.
ECG Graph paper

5. Unipolar precordial leads
This shows the position of the unipolar precordial leads. V1 at the 4th ICS RPSB, V2 at the same level LPSB, V4 at 5th ICS LMCL, V# in between V2 and V4, V% at 5th ICS LAAL and at Lmid axillary line V6.

6. Normal ECG

7. These are the waves and important intervals that you will see in an ECG tracing:
1.) P wave – corresponding to the atrial contraction
2.) PR segment – corresponds to the pause of the conduction of depolarization from the SA node to the AV node
3.) PR interval – corresponds to the length of time the depolarization from AV node proceeds to the AV node (normally ,0.20 s)
4.) QRS complex – ventricular contraction, normally <0.12 s
5.) ST segment – is the plateau phase of the ventricular repolarization
6.) ST interval – length of ventricular repolarization
7.) T wave – rapid phase of repolarization
8.) QT interval – length of ventricular contraction
9.) u wave – usually reflects hypokalemia

8. Guide in Reading ECG Standardization & technique Rhythm
Rate: atrial & ventricular
P wave morphology & duration
P-R interval
QRS complex morphology & duration
ST segment
T-wave
U wave
Q-T interval
Hypertrophy and enlargement
arrhythmias

9. Standardization Heart rate 60 - 100 beats/min bradycardia < 60
tachycardia > 100
PR interval – 0.20 sec
QRS < 0.12 sec
QRS axis º to + 110º
QTc < 0.47 sec males
< 0.48 sec females

10. Guide in Reading ECG Standardization & technique Rhythm
Rate: atrial & ventricular
Axis
P wave morphology & duration
P-R interval
QRS complex morphology & duration
ST segment
T-wave
U wave
Q-T interval
Hypertrophy and enlargement
arrhythmias

11. Rhythm
SA node – sinus
AV node – junctional
Ventricular rhythm

12. Rhythm Are there p waves?  sinus, atrial fibrillation
Do they look similar?
 MFAT, wandering pacemaker
Are they regular?
 AF
Does a QRS complex follow each p wave?
 SVT, junctional rhythm, ventricular rhythm

13. Guide in Reading ECG Standardization & technique Rhythm
Rate: atrial & ventricular
Axis
P wave morphology & duration
P-R interval
QRS complex morphology & duration
ST segment
T-wave
U wave
Q-T interval
Hypertrophy and enlargement
arrhythmias

14. Determination of Heart Rate
Heart rate assessment by “rule of 300”

15. Measurement of Rate Formula 1: 300 # big squares between R-R
# small squares between R-R

16. Determination of Heart Rate
Is the atrial rate same as ventricular rate?
PVC’s, PAC’s, 3rd degree AV block
Is there normal-looking QRS complex after each p wave?
What if there are no p waves?
Six second strip heart rate

17. RATE Sinus Bradycardia Sinus Tachycardia AV junctional rhythm
Inherent rate of 40-60/min
No p waves
Normal looking QRS complex
Ventricular rhythm
Inherent rate of 20-40/min
Bizaare-looking QRS complex

18. Guide in Reading ECG Standardization & technique Rhythm
Rate: atrial & ventricular
Axis
P wave morphology & duration
P-R interval
QRS complex morphology & duration
ST segment
T-wave
U wave
Q-T interval
Hypertrophy and enlargement
arrhythmias

19. Determination of Axis Hexaxial System
Axis refers to the direction of the movement of depolarization.
The QRS complex represents depolarization of the ventricles.
The mean QRS vector is the sum of all the smaller vectors of ventricular depolarization. Normally, it points downward and to the patient’s left, as this is the general direction of ventricular depolarization.
The limb leads are used to determine the axis.
If the heart is displaced, the axis is also displaced
- with hypertrophy, axis is displaced ipsilaterally
- in infraction, a necrotic area of the heart does not depolarize and the unopposed vectors from the other side draw the axis away from the infarct.
To obtain the limb leads, electrode are placed on the right arm, the left arm, and the left leg, forming a triangle.
A bipolar limb is formed by two electrodes, and it represents one side of the triangle. Each of these limb leads consists of a pair of electrodes, one is positive and the other negative.
Hexaxial System

20. A positive QRS deflection denotes depolarization towards the mean QRS, which is downwards and to the left.
For example, if the QRS complex in lead I is negative, it denotes that the vector points to the right side.
QRS axis

21. By eyeballing the limb leads, the tallest deflection or the degree perpendicular to the smallest deflection represents approximately the axis
Vectorial Analysis

22. Determination of Axis Axis = 90 x QRS in AVF
QRS in [ I] + QRS in [AVF]
Special cases:
negative QRS deflection in I
Add 90 to result

23. Guide in Reading ECG Standardization & technique Rhythm
Rate: atrial & ventricular
Axis
P wave morphology & duration
P-R interval
QRS complex morphology & duration
ST segment
T-wave
U wave
Q-T interval
Hypertrophy and enlargement
arrhythmias

24. These are the waves and important intervals that you will see in an ECG tracing:
1.) P wave – corresponding to the atrial contraction
2.) PR segment – corresponds to the pause of the conduction of depolarization from the SA node to the AV node
3.) PR interval – corresponds to the length of time the depolarization from AV node proceeds to the AV node (normally ,0.20 s)
4.) QRS complex – ventricular contraction, normally <0.12 s
5.) ST segment – is the plateau phase of the ventricular repolarization
6.) ST interval – length of ventricular repolarization
7.) T wave – rapid phase of repolarization
8.) QT interval – length of ventricular contraction
9.) u wave – usually reflects hypokalemia

25. P wave morphology and duration
No p waves
Atrial fibrillation
Multiple p waves
Multifocal atrial tachycardia
Wandering pacemaker
Notched p wave
Left atrial enlargement
Peaked p wave
Right atrial enlargement

26. Guide in Reading ECG Standardization & technique Rhythm
Rate: atrial & ventricular
Axis
P wave morphology & duration
P-R interval
QRS complex morphology & duration
ST segment
T-wave
U wave
Q-T interval
Hypertrophy and enlargement
arrhythmias

27. P-R Interval
These are the waves and important intervals that you will see in an ECG tracing:
1.) P wave – corresponding to the atrial contraction
2.) PR segment – corresponds to the pause of the conduction of depolarization from the SA node to the AV node
3.) PR interval – corresponds to the length of time the depolarization from AV node proceeds to the AV node (normally ,0.20 s)
4.) QRS complex – ventricular contraction, normally <0.12 s
5.) ST segment – is the plateau phase of the ventricular repolarization
6.) ST interval – length of ventricular repolarization
7.) T wave – rapid phase of repolarization
8.) QT interval – length of ventricular contraction
9.) u wave – usually reflects hypokalemia

28. P-R interval Prolongation Shortening Hypokalemia 1st degree AV block
Wolff-Parkinson White

29. Guide in Reading ECG Standardization & technique Rhythm
Rate: atrial & ventricular
Axis
P wave morphology & duration
P-R interval
QRS complex morphology & duration
ST segment
T-wave
U wave
Q-T interval
Hypertrophy and enlargement
arrhythmias

30. QRS morphology and duration
Normal looking
Supraventricular origin
Bizarre looking
Ventricular in origin
Paced rhythm

31. Guide in Reading ECG Standardization & technique Rhythm
Rate: atrial & ventricular
Axis
P wave morphology & duration
P-R interval
QRS complex morphology & duration
ST segment
T-wave
U wave
Q-T interval
Hypertrophy and enlargement
arrhythmias

32. ST segment Elevation depression Infarction >1mm in limb leads
>2 mm in chest leads
depression
Ischemia
>1 mm in all leads from the J point

33. Guide in Reading ECG Standardization & technique Rhythm
Rate: atrial & ventricular
Axis
P wave morphology & duration
P-R interval
QRS complex morphology & duration
ST segment
T-wave
U wave
Q-T interval
Hypertrophy and enlargement
arrhythmias

34. T and U waves T wave Shortening Hypokalemia 1st degree AV block
Wolff-Parkinson White

35. Guide in Reading ECG Standardization & technique Rhythm
Rate: atrial & ventricular
Axis
P wave morphology & duration
P-R interval
QRS complex morphology & duration
ST segment
T-wave
U wave
Q-T interval
Hypertrophy and enlargement
arrhythmias

36. Determination of QT interval
Corrected QT interval = QT (actual)
R-R

37. QT interval
prolongation
hypocalcemia
shortening
hypercalcemia

38. Chamber Enlargement

39. Atrial Enlargement (due to chronic lung disease or pulmonay embolus
Since the P wave represents the depolarization and contraction of both atria, we examine the P wave for evidence of atrial enlargement.

40. Atrial Enlargement (commonly seen in mitral valve disease)B V1 II V1

42. Ventricular Enlargement

43. Ventricular Enlargement
Right Ventricular Hypertrophy
R in V1 + S in V5-V6 >11 mm
R in V1 >7mm
R:S in V1 >1
RAD > +90 degrees

46. Ischemic Heart Disease

47. Anatomy of Myocardial Infarction
*LAD = left anterior descending aretery; LCX = left circumflex artery
LM = left main artery; PDA = posterior descending artery;
PL = posterolateral branches

48. Evolution of Infarct ST segment elevation
Progressive decrease in ST segment elevation
Q wave formation
T wave flattening/inversion
Q wave with upright T wave

49. Significant Q wave

50. RULES on Q waves Not significant in aVR
Ignored in V1 unless with abnormalities in other precordial leads
Ignored in III unless with abnormalities in II, AVF more reliable if with St-T segment changes
Not significant if located in V1-V3 in LBBB
Significant in V1-V2 in the presence of RBBB
Pathologic if >= 0.04 sec and >25% of R wave amplitude

51. RHYTHM DISORDERS

52. ATRIAL Arrhythmias Atrial fibrillation Atrial flutter
Wandering Pacemaker
Multifocal Atrial tachycardia

53. ATRIAL FIBRILLATION
Most common sustained arrhythmia associated with increased CV mortality and morbidity
Prevalence increasing with age, doubling with each successive decade, 70% in ages 65-85
Multiplier effect on risk
3-5x stroke
3x CHF
1.5-3x death
Associated with heart disease but ~30% are without underlying heart disease

54. ATRIAL FIBRILLATION
Rapid and irregular atrial fibrillatory waves at a rate of 350 to 600/minute
CRITERIA
Absent P waves
F waves vary in amplitude, morphology and intervals
R-R intervals are irregularly irregular
Ventricular rate usually ranges from
QRS complexes are narrow unless AV conduction is abnormal
Hypothesized to be due to multiple wavelets in the atrium competing for the conduction to the AV node

55. ATRIAL FIBRILLATION

56. ATRIAL FLUTTER Atrial rate of 220 to 350/minute CRITERIA
Absent p waves
Biphasic saw-toothed flutter waves, fairly regular
F waves vary in amplitude, morphology and intervals
R-R intervals are irregularly irregular
Ventricular rate usually ranges from
QRS complexes are narrow unless AV conduction is abnormal
Hypothesized to be due to multiple wavelets in the atrium competing for the conduction to the AV node

57. ATRIAL FLUTTER

58. Escape Rhythm/Beat Atrial Junctional Ventricular
Sinus arrest causing escape rhythm
With p’ waves
Junctional
No P waves
40-60/min inherent rate
Produces a series of lone QRS complexes
Ventricular
- may occur in complete AV block

59. Escape Rhythm/Beat

60. Sinoatrial block Complete failure of a P wave to appear
A cycle appears which is twice the anticipated P-P interval
Transient doubling of P-P interval
SA exit block
No visible P-QRST complex for more than 1 cycle
Normal P wave morphology, before and after the pause
Pause is preceded and followed by a normal P-P cycle
P-P interval is a mutliple of the normal P-P interval

61. SA block

62. SINUS ARREST vs SINUS PAUSE

63. Wandering Pacemaker
Impulses originate from different foci in the atrium and even AV node
Sinus node may still be dominant
>= 3 P wave morphologies, with varying P-R intervals, resulting in varying R-R intervals
Heart rate <100
May be seen in
Increased vagal tone
Digitalis effect
Organic heart disease

64. Wandering Pacemaker

66. Multifocal Atrial Tachycardia
Irregular atrial rate > 100
P wave shows >= 3 different morphologic patterns and varying PR intervals
Varying P-P and P-R intervals result in avrying R-R intervals

67. Multifocal Atrial Tachycardia

68. HEART BLOCKS 1st degree 2nd degree Complete AV block
Type 1 Wenkeboch
Type 2 Mobitz II
Complete AV block
Bundle Branch Block
Right bundle branch block
Left bundle branch block
Hemiblocks
Left anterior hemiblock
Left posterior hemiblock

69. 1st degree 2nd degree (type1 and 2) 3rd degree PR interval > 0.20s
Type 1 – PR interval becomes longer until depolarization is not conducted anymore
Type 2 – AV conduction is blocked
3rd degree
AV dissociation
Variable PR and RP intervals
QRS rate is usually constant and lies within the range of beats /min

74. Trifascicular Conduction System

75. Right Bundle Branch Block
Lead V1 late intrinsicoid, M-shaped QRS (RSR pattern)
Lead V6 early intrinsicoid, wide S wave
Lead I wide S wave

76. Right Bundle Branch Block
Associated with
RHD
Cor pulmonale/RVH
Myocarditis
IHD
Degenerative disease of the conduction system
Pulmonary embolus
ASD

77. Right Bundle Branch Block

78. Left Bundle Branch Block
Lead V1 QS or rS
Lead V6 late intrinsicoid, no Q waves, monophasic R
Lead I monophasis R, no Q wave

79. Left Bundle Branch Block
Associated with
CAD
HHD
Dilated cardiomyopathy
-- unusual for LBBB to exist in the absence of organic disease

80. Left Bundle Branch Block

81. Left Anterior Hemiblock
LAD (usually -30 to -60 degrees)
Small Q in leads I and aVL, small R in II, III and aVF
Usually normal QRS duration
Late intrinsicoid deflection in aVL
Increased QRS voltage in limb leads

82. Left Anterior Hemiblock
Usually benign in the absence of apparent organic heart disease and not associated with block in the other fascicles
Can also occur in
CAD
Chagas disease
Infiltrative and inflammatory diseases
CHDs
Sclerodegenerative disorder

83. Left Anterior Hemiblock

84. Left Posterior Hemiblock
RAD (usually degrees)
Small R in leads I and aVL, small Q in II, III and aVF
Usually normal QRS duration
Late intrinsicoid deflection in aVF
Increased QRS voltage in limb leads
No evidence of RVH

85. Left Posterior Hemiblock
Can occur in
Cardiomyopathies
Myocarditis
Hyperkalemia
Acute cor pulmonale
chronic degeneerative and fibrotic processes of the conducting system
Aretriosclerotic cardiovascular disease

86. Left Posterior Hemiblock

87. Bifascicular Block Complete LBBB RBBB with either LAHB or LPHB
Duration of QRS complex is prolonged to 0.12s

88. Bifascicular Block

89. Trifascicular Block
Bifascicular block associated with 1st degree AV block

90. Trifascicular Block

91. Premature Complexes Premature Atrial Complex
Junctional Premature Beats
Ventricular Premature Beats

92. Premature Complexes - PACs
Premature atrial activation arising from a site other than the sinus node
P wave occuring relatively early in the cardiac cyle
- with a different morphology from the sinus P wave
PR interval different from that during the sinus rhythm

93. Premature Complexes - PACs
Not life-threatening by themselves
But may also start a VT
May be asymptomatic or cause a sensationof “skipping” or palpitations
May be associated with normal conduction or aberrant conduction

94. Premature Complexes - PACs

95. Premature Complexes – Junctional Premature Beats
Arise from the AV node or in the His bundle
A premature normal QRS complex is closely accompanied by an “upside down” P wave

96. Premature Complexes – Ventricular Premature Beats
Duration of more than 0.12s
Bizarre morphology T wave in the opposite direction from the QRS vector
A fully compensatory pause
Ventricular bigeminy, trigeminy, quadrigeminy, couplet

97. Premature Complexes – Ventricular Premature Beats
May be present in
Normal individuals
MVP
Hypertension and LVH
Chronic HD
Acute MI
cardiomyopathy

98. Poor R wave progression Low QRS
Miscellaneous
Poor R wave progression
< 3mm R wave in V3
Low QRS
< 5mm QRS amplitude in limb leads
<10mm QRS amplitude in chest leads

99. Questions???