Electrocardiography for Students

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

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

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

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

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

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

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

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

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

The Principle
ECG Machine is a modified galvanometer in which the recordings are made by electrodes placed on the body surface, sensing the electrical impulses of heart
Positive deflection
Current moving towards +ve electrode
+
Negative deflection
Current moving away from +ve electrode
+
10

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

The Graphical Recording
12

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

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

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)

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

Rest of it is calculated mentally
If RR = 1 BD, HR will be = 300/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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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
Thank You for the Patient Listening

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Electrocardiography for Students

by Prof. Dr. Aswini Kumar on Aug 31, 2009

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Electrocardiography for Students — Presentation Transcript