ECG Simplified for Students

1. Electrocardiography Dr. S. Aswini Kumar. MD Professor of Medicine Medical College Hospital Thiruvananthapuram 1

2. Definition: ECG is the graphical recording of electrical activity of human heart recorded from the body surface using multiple electrodes placed over the body 2

3. Advantages ECG is immediately available and it is non-invasive as well as inexpensive Not only that, it is a highly versatile tool 3

4. Importance Interpretation of the hearts electrical messages is a valuable and easily attained skill It is useful in the diagnosis and treatment 4

5. Not a “Bali kera mala” It is easy, provided you learn it systematically and thoroughly and practice it daily ECG reading is not a Bali Kera Mala. 5

6. Uses of ECG: Heart Rate Normal / Tachycardia / Bradycardia Arrhythmias Ventricular / Supraventricular Heart Blocks AV Nodal / RBBB / LBBB Coronary Circulation Ischemia / Injury / Infarct Chamber Enlargement LAE / RAE / LVH / RVH Electrical Axis Normal / Right axis / Left axis Electrolyte Imbalance Hypokalemia/ Hyperkalemia Carditis Myocarditis/ Pericarditis Drug Effect Digoxin / Quinidine / Adriamycin There are multiple uses of ECG in the general practice and consultant practice as well as in internal medicine 6

7. Willem Einthoven It was Einthoven who discovered the ECG machine It was in 1890 and for this epoch making invention he was awarded Nobel Prize in the year 1924 7

8. ECG Machine The ancient ECG machine occupied a whole room The patient dipping both hands and the left leg in buckets containing salted solution 8

9. Modern ECG Machine The present day ECG machines are very compact, portable as well as computerized Some capable of producing multi channel recordings 9

11. ECG Paper The ECG paper is actually a black paper on which a heat sensitive, white or rose substance is coated This coating is erased by the heated stylus Black paper No ink Heat sensitive Cheap 11

12. The Graphical Recording 12

13. The Duration The duration is measured in the horizontal direction. The calculation is, one small division is equal to 1mm and it is equivalent to 0.04 seconds 13

14. Conversion When one small division horizontally (SD) = 0.04sec Then 2 SD = 0.08 sec and 3SD =0.12 sec , 4SD = 0.16sec, 5SD = 0.20sec so on and so forth 14

15. Amplitude 15 Lead V6 The amplitude is measured in the vertical direction. The calculation is one mille volt of current produces a deflection of 10 small divisions (sd)

16. Amplitude simplified However amplitude of waves in are expressed only in mm of height of or depth of the waves. Here the ‘R’ wave is 16mm and ‘S’ wave is 6 mm 16mm 6mm 16

17. Leads in ECG The ECG discovered by Einthoven had only one set consisting of three leads I, II & III Later three more sets were added to this 17

18. Standard Limb Leads Standard limb leads I, II and III are obtained using a +ve and -ve electrode placed on the wrists of upper limbs and ankle of the left lower limb   I   III II   18

19. Limb leads I, II and III Originally discovered by Einthoven, when Limb leads I, II and III form a triangle named after him The heart is considered to be situated in the center 19

20. Augmented Unipolar Lead aVR Exploring Electrode Neutral Electrode Here a neutral electrode is made by joining the left upper limb and left lower limb. An exploring electrode is placed in the right upper limb 20

21. Augmented Unipolar Lead aVL Exploring Electrode Neutral Electrode Here a neutral electrode is made by joining the right upper limb and left lower limb An exploring electrode is placed in the left upper limb 21

22. Augmented Unipolar Lead aVF Here a neutral electrode is made by joining the left upper limb and right upper limb The exploring electrode is placed in the left lower limb Neutral Electrode Exploring Electrode 22

23. Chest Leads V1 to V6 Neutral electrode is made by connecting all 3 limbs Exploring Electrodes are then placed over various points on left side of the chest to record the chest leads 23

24. Right Chest Leads Right sided leads V3R and V4R can recorded by placing electrodes on the right chest They correspond to leads V3 and V4 on the left sides 24

25. Higher Chest Leads Higher Chest leads HC1 and HC2 may be recorded by placing electrodes one space above the chest leads. This is to map the higher level of cardiac activity 25

26. The Cardiac Cycle The P, Q, R, S, T & U waves were named so by Einthoven. Together they represent the sequence of events of the human cardiac cycle 26

27. The waves and intervals The waves are regrouped as P wave, QRS complex, ST segment, T wave and U wave. The intervals of importance are PR, QRS, QT & RR 27

28. Electrical Correlation P wave represents atrial depolarization, QRS complex - ventricular depolarization, T - ventricular repolarization; Atrial repolarization is hidden within PR or QRS 28

29. Measurements The measurements required are the duration of P wave, PR interval, ST segment, T wave height, The RR interval, QRS duration and QT interval 29

30. Long leads Short leads Long leads Normally, one complex with all components p, q, r, s, t and u waves is good enough for interpretation of ECG But for assessment of arrhythmias one needs long lead 30

31. Step 1. Standardization It is the first lead of the electrocardiogram, the standard against which other leads are to be read It is the square waves seen at the beginning of the ECG 31

32. What is Standardization? 10 small divisions 1 mV current When 1 milli volt of current is given by the machine it produces a square wave deflection of 10 small divisions When ECG is recorded this amplitude is applied 32

33. What is half standardization? 5 small divisions 1 mV current Here even when 1 milli volt of current is applied there is a deflection of only five small divisions This is made so, if the deflections are very tall 33

34. Look for standardization in every ECG So the first step in reading an ECG is to look for the presence and correctness of the standardization Only if it is so, the rest of the ECG is read 34

35. Step 1: Standardization Step 01. Standardization: 1mv = 10sd 35 I looked into the ECG I found that there is a standardization lead It was looking like a rectangle The height was 10mm There were no half standardization leads

36. Step 2: Calculation of Heart rate If the rhythm is regular, count the number of big divisions between two adjacent R waves Then divide the 300 with that value to get the heart rate 36

37. Rest of it is calculated mentally If RR = 1 BD, HR will be = 300/min. If RR = 2 BD, HR will be = 150/min. If RR = 3 BD, HR will be = 100/min. If RR = 4 BD, HR will be = 75/min. If RR = 5 BD, HR will be = 60/min. If RR = 6 BD, HR will be = 50/min. Only this amount of accuracy in calculating the heart rate is required in most instances Otherwise divide 1500 by the number of small divisions 37

38. Heart Rate in Irregular Rhythm If there is Atrial Fibrillation, count the number of QRS complexes within 6 seconds of ECG paper Then multiply by 10 to get heart rate in 60 seconds 38

39. Step : Rhythm of the Heart Rhythm of heart is the regularity or irregularity of the heart action It has to be studied using a long lead II or V1 39

40. Normal Sinus Rhythm Normal sinus rhythm is said to be present if the heart rate is between 60 and 100 and every P wave is followed by a QRS complex and a T wave and intervals normal 40

41. Step 3: The Rhythm The rhythm appeared to be regular The heart rate calculated was 75 per minute Each P was followed by a QRS and T PR interval and QRS durations were normal The shape of QRS was normal Step 02 - Heart Rate: 75/min 41

42. Step 4 – Electrical Axis It is the net or ultimate direction of conduction of the cardiac impulse from SA node to the ventricular apex which can be represented as a straight line vector 42

43. Determining Axis Axis is determined by studying leads I and III alone. If the net deflection is upright in these two leads, the axis is considered as normal I II 43

44. Normal Electrical Axis In the above ECG the lead I shows an upright wave with net positive deflection and lead III shows a net positive wave with upward deflection. Hence axis is normal 44

45. Right Axis Deviation In the above ECG the lead I shows a downward wave with net negative deflection and lead III shows a net positive wave with +ve deflection. Hence axis is RIGHT 45

46. Left Axis Deviation The lead I shows a positive wave with net positive deflection and lead III shows a net negative wave with negative deflection. Hence axis is LEFT 46

47. Step 4: Electrical Axis of Heart I looked into leads ! And III In lead I there was a positive and negative But positive wave was more In lead I the net deflection was positive In lead III also the net deflection was positive Step 04 - Electrical Axis: Normal 47

48. Step 5: P wave The normal P wave is upward convex in shape and prominently seen in leads II and V1 So look into leads II and V1 for the details 48

49. Normal P wave The normal P wave is not more than 2.5 mm height and not more than 2.5 mm in width If it more than this it is abnormal 49

50. P Mitrale When P wave is broad and notched it indicates Left Atrial Enlargement and it is most often seen in patients with Rheumatic Mitral Stenosis 50

51. P Pulmonale When P wave is tall and peaked it indicates Right atrial enlargement It is most often seen in Chronic Corpulmonale 51

52. Step 5: P wave I studied the P wave dimensions It was 2 mm wide It was 2.5 mm high P wave shape was normal in lead II P was biphasic in V1 and terminal negative Step 05 – P wave: Normal 52

53. Step 6: PR Interval The physiological necessity, for the AV Nodal delay, which causes the normal PR interval is that, the same SA Nodal impulse has to activate, both atria & ventricles 53

54. Normal PR Interval The Normal PR Interval is 3-5 small divisions, when measured from the beginning of P to beginning of QRS In other words it is 0.12 to 0.20 seconds 54

55. Prolonged PR Interval Prolonged PR interval is said to be present if the PR interval is equal to or more than 0.21 sec It is seen in Acute Rheumatic Fever and I degree HB 55

56. Short PR Interval PR interval is said to be short when it is less than 0.12 seconds in duration It is seen in WPW Syndrome and Junctional Rhythm 56

57. ECG showing short PR interval It is a sinus rhythm with short PR interval and ventricular pre-excitation syndrome possibly due to WPW There is in addition a Delta wave 57

58. Step 6: PR Interval I looked at the PR segment I measured the PR interval It was found to be 4 small divisions It meant that it is 0.16 seconds in duration It is with in the normal ranges Step 06 – PR interval: Normal 58

59. Step 7: Q Wave Q wave is defined as the first negative deflection of the QRS Complex and it is normally present only in a few leads viz. Lead III, II, V5 & V6 and they are very small 59

60. There can be ‘no Q’ situation But q waves are not always present in all the leads of all persons, unlike the other waves A small q may be present in some leads No Q Q T P P QRS P T P QRS 60

61. Significance of Q waves The presence of a significant Q wave is highly suggestive of a transmural myocardial infarction It also means that the coronary artery is totally occluded 61

62. What is an insignificant ‘Q wave’? When the ‘q wave’ is very small in size (less than 0.04mm in width) it is called an insignificant q wave Then it is an isolated finding in one lead. Small q 62

63. Small or insignificant q waves are seen usually in leads III, II, V5 and V6, in normal persons. Rest of the leads in a normal person does not show any significant q wave In which leads small ‘q’ waves are seen? Lead III Lead II Lead V5 Lead V6 63

64. Pathological Q wave A ‘significant Q’ or ‘pathological Q’ is one which is more than 0.04mm in width. It may also be more than 25% of the R wave height in the same lead >0.04mm P Q P Q 64

65. Why is Q very important? Presence of significant Q wave indicates the diagnosis of Myocardial infarction either acute or old It is usually preceded by the classical chest pain . 65

66. Whether Acute MI or Old MI? If it is, accompanied by other evidence of acute Myocardial Infarction, like ST elevation or T wave inversion it is acute; otherwise it is old . 66

67. Anterior wall Infarction In Anterior wall Myocardial Infarction the changes of MI are seen in V2-V4 If V1 also shows changes the septum is involved 67

68. Inferior wall Infarction In Inferior Wall Myocardial Infarction the changes of MI are seen in II, III and aVF If V1 also shows changes the septum is involved . 68

69. Step 7: Q wave I looked for any q waves Small q were present in V5 and V6 Rest of the leads were not showing any q He q present were not wide None of them > 0.04 second Step 07 – Q wave: Nil pathological 69

70. QRS Duration Measurement QRS duration is measured from the beginning of QRS to the end of QRS Irrespective of the type and waves in the QRS 70

71. QRS Patterns QRS patterns vary from individuall to individual and from lead to lead They don’t have much significance 71

72. Step 8: QRS duration I looked at the QRS complexes They were looking normal The duration, I measured It was 0.10 seconds The pattern were numerous Step 08 – QRS Duration: Normal 72

73. Step 8: ST segment ST segment is that portion of the base line from the S wave to the beginning of T wave, Normally, it is iso-electric ie. at the same level as that of the baseline ST segment 73

74. ST segment elevation ST segment elevation is the elevation of the beginning of ST segment from the baseline, when compared to the isoelectric line or the PR segment ST segment elevation ST segment 74

75. What is J point? J point is the point at which the S wave ends and the ST segment begins It is usually seen as a definite point of turn J point elevation J Point 75

76. Significance of ST elevation Elevation of the ST segment is considered to be due to myocardial injury in coronary artery disease and it is the single most important criterion of thrombolytic therapy 76

77. Pathophysiological Co-relation The degree of ST elevation in the ECG directly correlates with the pathophysiology of CAD Hence it the indication for thrombolysis 77

78. Differential diagnosis of ST elevation Pericarditis is characterized by the presence of ST elevation with upward concavity, present almost in all the leads and associated with PR segment depression 78

79. Early Repolarization It is a normal variant seen mostly in young males characterized by J point elevation To be differentiated from Acute MI and Pericarditis 79

80. Comparison of ECG changes ST/T Ratio in V6 of <0.25 against Pericarditis and less ST(equal to or less than 0.05mV) against Acute Myocardial Infarction 80

81. Whether there is ST depression? The ST segment is normally at the same level as that of the iso-electric line/PR segment. When it is depressed by1mm from the baseline, it is called ST depression Normal ST segment ST segment Depression 81

82. What is ST depression due to? ST depression in ECG is due to the presence of Ischemia to the myocardium It occurs in Angina 82

83. What is myocardial Ischemia? Myocardial ischemia may result in temporary or permanent damage to the myocardium But usually not 83

84. Causes of ST depression Down sloping ST elevation is usually due to ventricular strain associated with a relative ischemia, whereas, horizontal ST depression is due to absolute ischemia Horizontal ST segment depression Down sloping ST segment depression 84

85. Step 9: ST segment I looked at the ST segment after each QRS They were flat and isoelectric I compared them with the P segments They were at the same level There was no point elevation or depression Step 09 – ST segment is isoelectric 85

86. Step 10. T wave T wave is the upward convex wave following the QRS complex and it represents ventricular repolarization Normal T wave 86

87. Normal T wave The normal pattern of T wave is upward and convex in all the leads of the ECG except aVR and V1 ; it is inverted in these leads 87

88. What is tall peaked T wave? T wave is said to be tall and peaked when it is very tall and equal to or more than the preceding R wave and along with an elevated ST suggestive of a acute MI Tall peaked T wave Normal T wave 88

89. Significance of peaked T Tall and peaked T waves along with ST elevation in a set of ECG leads are the earliest evidence of acute coronary syndrome called Hyperacute Myocardial Infarction 89

90. Other important cause of tall peaked T Peaked T, along with decreased p wave amplitude and widening of QRS complex suggest hyperkalemia It is also a potentially fatal disorder 90

91. Types of T wave inversion In Acute MI the terminal portion of the peaked T wave is inverted resulting in a biphasic T wave; In other forms of ischemia the T wave is usually symmetrically inverted Symmetrical T Inversion Biphasic T wave 91

92. ECG with T inversions ST depression along with T wave inversions are seen in leads II, III and aVF and the chest leads V4, V5 and V6 suggesting ischemia of the inferior and lateral walls 92

93. Step 10: T wave I looked at the T wave in all leads They were upright in all leads With the exception of leads aVR and V1 T shape was now inspected There were no peaked or inverted T waves Step 10 – T wave: Normal 93

94. Changes occurring in Acute MI In normal persons ECG the q wave is absent or insignificant, ST isoelectric and T upright in all leads There is no evidence of MI 94

95. ECG changes after Acute MI After Acute Myocardial Infarction, q wave appears, ST is elevated and the T wave is inverted in the leads affected The evidence of MI 95

96. Progressive changes during MI Seen is the normal ECG followed by the progressive changes in acute myocardial infarction Peaked T, ST elevation, loss of R and T inversion 96

97. Progressive changes after MI ECG changes in the post MI periodThe ST elevation gets resolved, T inversion gradually disappears and the Q waves if any persist 97

98. Anterior Wall MI Changes of Acute MI , when seen in the anterior chest leads, from V1 to V4 it is diagnostic of Anterior Wall MI; if lead V1 is involved it is termed anteroseptal MI 98

99. Coronary Occlusion Anterior wall myocardial infarction means that the left anterior descending branch of the left coronary artery is occluded by a thrombus 99

100. Acute Anteroseptal MI ST elevation and tall peaked T waves are seen in the anterior precordial leads No q waves have appeared 100

101. Antero-septal MI evolved phase Here the ST is still elevated the T wave is upright in the chest leads V1 to V4 Q waves have appeared in the same leads 101

102. Lateral Wall Infarction Changes of Acute MI , when seen in the lateral chest leads, from 1, aVL, V5 V6, it is diagnostic of Lateral Wall Myocardial Infarction 102

103. Deep Circumflex occlusion It is also inferred from this, that it is the deep circumflex branch of the left coronary artery, is occluded, either by a plaque or thrombus 103

104. Acute Myocardial Infarction Diffuse ST elevation with reciprocal changes Anterior lateral and inferior walls are involved and there is atrial fibrillation also 104

105. Inferior Wall Infarction Changes of Acute Myocardial Infarction, when seen in the inferior chest leads, namely II, III and aVF is diagnostic of Inferior Wall MI 105

106. Right coronary artery occlusion It is also inferred from this, that it is the right coronary artery, which supplies the inferior or diaphragmatic surface, is occluded, either by a plaque or thrombus 106

107. Acute Inferior Wall MI – Early stage Changes are seen in the leads II, III and aVF; hence it is Inferior wall MI There is ST elevation and reciprocal changes also 107

108. Acute Inferior Wall MI in ECG There is ST elevation, Upright and peaked waves in II, II and aVF It is acute Inferior wall MI 108

109. Antero-lateral Infarction Changes of Acute MI are seen in all the anterior chest leads, from V1 through V6 It is diagnostic of Antero-lateral Wall MI 109

110. Left Coronary Stem Occlusion The left coronary artery, which supplies the whole of the anterior wall of heart is occluded at the stem, involving the area supplied by both the branches 110

111. True Posterior MI Changes are in the V1 lead of ECG as mirror image. These are Tall R instead of Q, ST depression instead of ST elevation and upright T instead of T inversion 111

112. Right Ventricular Infarction The changes of myocardial infarction are visible in the right ventricular leads, V3R & V4R It is a right ventricular Infarction 112

113. ECG of RVMI Right sided leads shown separately on the right side of the panel shows ST elevation The diagnosis is Inferior Wall MI + RV MI 113

114. Transmural and subendocardial Previously, abnormal Q waves were considered to be markers of trans-mural MI, while sub-endocardial infarcts were thought not to produce Q waves 114

115. Q waves are more important Now we know that Trans-mural Infarcts may occur without presence of Q waves and subendocardial infarcts may produce Q waves 115

116. ECG in ACS When a patient presents with acute onset of chest pain, ECG is the first line of investigation Depending upon ECG findings further assessment made 116

117. Acute Coronary Syndrome The algorithmic management of a patient with Acute Coronary Syndrome is also now based on the ECG Cardiac markers assist the diagnosis 117

118. Step 11: Right Ventricular Hyprtrophy Normally the R wave in lead V1 is less than S wave in the same lead. If R wave height is found to be more than S wave depth in lead V1 it is the voltage criteria for RVH Lead V1 Lead V1 118

119. Right Ventricular Hypertrophy The height of the R wave in V1 and depth of the S wave in V1 is measured and these are compared The R wave in V1 is taller than the S wave in V1 119

120. Step 11: RVH by voltage criteria I looked at lead V1 Measured the height of r wave – 4 mm I looked at lead V1 again Measured the depth of S wave – 16 mm The r wave height is less than S wave depth Step 11 – No RVH by voltage criteria 120

121. Step 12: S in V1 + R in V6 If the depth of S wave in lead V1 + R wave height in V6 is more than 35mm, it satisfies the voltage criteria for Left Ventricular Hypertrophy Lead V1 Lead V6 121

122. Left ventricular hypertrophy The depth of the S wave in V1 is measured and added to the height of the R wave in V6 The total is more than 35 mm It is LVH 122

123. Step 12: LVH by voltage criteria I looked at lead V1 Measured the depth of S wave – 12 mm I looked at lead V6 Measured the height of R wave – 16 mm Added these two. The result was 28 mm Step 12 – No LVH by voltage criteria 123

124. Thus ECG is read simply 1. Std 2. Rate 3. Rhythm 4. Axis 5. P 6. PR 7. Q 8. QRS 9. ST 10. T 11. R/S in V1 12. SV1+RV6 124

125. 125 Thank You for the Patient Listening