2. ELECTROCARDIOGRAM
➤ The electrocardiogram (ECG or EKG) is a special graph that
represents the electrical activity of the heart from one instant
to the next.
➤ ECG provides a time-voltage chart of the heartbeat
➤ It is a graphic recording of electric potentials generated by
the heart
3. THE ECG PAPER
➤ Horizontally
-one small box -0.04s
-one large box- 0.20s
➤ Vertically
- one small box -0.1 mV
- one large box -0.5 mV
4. STANDARDISATION OF ECG
➤ Conventionally 1 mV electrical activity will result in a 10 mm
vertical deflection
➤ Amplitude =0.1 mV/mm(10mm = 1mV)
➤ ECG speed= 25 mm/sec
5. ECG LEADS
➤ 12- Lead ECG is commonly used
➤ 10 electrodes required to produce 12-lead ECG
➤ 4 Electrodes on all 4 limbs(RA,LL,LA,RL),6 Electrodes on
precordium (V1-V6)
➤ Precordial lead placement
6. ➤ Right sided ECG electrode placement
➤ A complete set of right sided leads is obtained by placing leads V1-6
in a mirror image position on the right side of the chest
➤ It can be simpler to leave V1 and V2 in their usual position and just
transfer leads V3-6 to the right side of chest
➤ The most useful electrode is V4R,which is obtained by placing the
V4 electrode in the 5th right ICS in midclavicular line
➤ ST elevation in V4R has a sensitivity of 88%,specificity of 78% and
diagnostic accuracy of 83% in diagnosing RV MI
7. Posterior Leads
➤ Leads V7-V9 are placed on the posterior chest wall
➤ V7- Left posterior axillary line, in the same horizontal plane as V6
➤ V8- Tip of the left scapula, in the same horizontal plane as V6
➤ V9- Left parasternal region, in the same horizontal plane as V6
➤ Useful for detecting Posterior MI
8. ECG LEADS
➤ Detect the voltages of the cardiac currents
➤ The usual way of recording voltages from the heart is with the 12
standard ECG leads( connections or derivations)
➤ The leads actually show the difference in voltage(Potential) among
electrodes placed on the surface of the body
➤ The leads can be divided into two sub groups ; the six limb leads
(I,II,III,aVR,aVL and aVF) and the six chest(precordial ) leads-V1-6
➤ Electrical impulse that travels towards the electrode produces an
upright(“positive”) deflection
9. ➤ Electrical impulse that travels away from the electrode produces an
downward(“Negative”) deflection
➤ Electrical impulse that travels perpendicular to the electrode
produces an Equiphasic deflection
14. NORMAL ECG
➤ P WAVE - Atrial depolarisation
➤ QRS complex - Ventricular depolarisation
➤ T wave - Ventricular repolarisation
➤ U wave - Remains uncertain
15. INTERPRETATION OF AN ECG
➤ Heart rate
➤ Rhythm
➤ Standardisation
➤ Cardiac Axis
➤ P wave
➤ PR interval
➤ QRS complex
➤ ST segment
➤ QT interval (Include T and U wave)
➤ Chamber enlargement
➤ Specific changes
➤ Other ECG signs
16. Initial features to look for on an ECG
➤ Most important thing ,always interpret the ECG in the clinical
context with things like age,gender,time,patient symptoms and
clinical features
➤ Also check for lead placement errors
➤ Limb leads : 1. check aVR for upside down P,QRS and T waves,
2.aVR and aVL should generally be mirror images
➤ Chest leads : look for RS pattern in V1- changing progressively to
QR pattern in V6
17. DETERMINING THE HEART RATE
➤ As a general interpretation, look at the lead II at the bottom part of
the ECG strip.
➤ This lead is the rhythm strip,which shows the rhythm for the whole
time the ECG is recorded.
➤ Look at the number of squares between R-R interval
➤ Rule of 300/1500
➤ Rate =300 / No of big squares between R-R interval
➤ Rate= 1500/ No of small squares between R-R interval
18. REGULAR RHYTHM
➤ Rate = 300/ number of LARGE square between consecutive R
waves
VERY FAST RHYTHM
➤ Rate = 1500/ number of SMALL squares between
consecutive R waves
SLOW or IRREGULAR RHYTHM
➤ Rate= Number of R waves X 6
➤ The number of complexes (count R waves) on the rhythm strip gives
the average rate over a ten second period.This is multiplied by 6(10
seconds x 6= 1 minute) to give the average beats per minute
20. RHYTHM
➤ Look at P waves and their relationship to QRS complexes
➤ Lead II is commonly used
➤ Regular or irregular
➤ If in doubt,use a paper strip to map out consecutive beats and see
whether the rate is same further along the ECG
➤ Measure the ventricular rhythm by measuring the R-R interval and
atrial rhythm by measuring P-P interval
21. AXIS
➤ The direction of an ECG waveform in the frontal plane measured in
degrees
➤ Represents the flow of the majority of electrical activity
➤ Normally the QRS complex is measured
➤ As QRS axis is being defined in the frontal plane,the QRS is being
described only in reference to the six extremity leads
➤ In calculating the mean QRS axis,towards which lead,the QRS
complex predominantly oriented is determined
➤ As a general rule,the mean QRS axis points midway between any
two leads that show tall R waves of equal height
22. THE QRS AXIS
➤ Normal QRS axis from 0 to +90 degrees
➤ 0 to -30 degrees referred to as slight left axis deviation
➤ -30 to -90 degrees referred to as extreme left axis deviation
➤ +90 to +180 is referred to as right axis deviation
➤ -90 to -180 is referred to as extreme right axis deviation/Northwest
region
23. Methods of ECG Axis interpretation
➤ The Quadrant Method – (Lead I and aVF)
➤ Three lead analysis- (LeadI,LeadII and aVF)
➤ Isoelectric lead analysis
24. The Quadrant method
➤ The most effective way to estimate axis is to look at LEAD I and
LEAD aVF
➤ Examine the QRS complex in each lead and determine if it is
positive,Isoelectric(Equiphasic) or Negative:
25. ➤ A positive QRS in lead I puts the axis in roughly the same direction
as lead I
➤ A positive QRS in lead aVF similarly aligns the axis with lead aVF
➤ Combining both coloured areas- the quadrant of overlap determines
the axis .So if lead I and aVF are both positive,the axis is between 0
and +90 degrees(i.e. normal axis)
26. THE QUADRANT APPROACH
➤ Summary table
Positive
Negativ
e
Positive
Normal
axis
LAD
Negativ
e
RAD
Indeter
minate
axis
27. Three lead analysis
➤ Add lead II to the analysis of Lead I and aVF
➤ A positive QRS in lead II puts the axis in roughly the same direction
as lead I
➤ A positive QRS in lead II similarly aligns the axis with lead II
➤ We can then combine both coloured areas and the area of overlap
determines the axis .So if lead I and II are both positive,the axis is
between -30 and +90 degrees(i.e.normal axis)
28. ➤ The combined evaluation of lead I,lead II and aVF –allows rapid and
accurate QRS assessment
➤ The addition of lead II can help determine pathological LAD from
normal axis/physiological LAD
➤ Lead III or aVF can both be used in three lead analysis
30. The Isoelectric method
➤ This method allows a more precise estimation of QRS axis,using the
diagram below
➤ If the QRS is ISOELECTRIC(equiphasic) in any given lead,the axis
is at 90 degrees to this lead
33. P WAVE
➤ Always positive in lead I and lead II
➤ Always negative in lead aVR
➤ <3 small squares in duration
➤ <2.5 small squares in amplitude
➤ Commonly biphasic in lead V1
➤ Best seen in lead II
34. Abnormal P waves
➤ Left atrial enlargement produces a broad,bifid P wave in lead II (P
mitrale) and enlarges the terminal negative portion of the P wave in
V1
➤ In lead II –1. Bifid P wave with > 40 ms between the two peaks,2.
Total P wave duration > 110 ms
➤ In V1- 1.Biphasic P wave with terminal negative portion > 40 ms
duration and >1 mm deep
35.
36. Right Atrial enlargement
➤ It produces a peaked P wave ( P Pulmonale) with amplitude:
➤ >2.5 mm in the inferior leads(II,III,aVF)
➤ >1.5 mm in V1 and V2
37. QRS COMPLEXES
➤ An initial downward deflection after the P wave is termed a Q wave
➤ An initial upward deflection after the P wave is termed an R wave
➤ Not every QRS complex contain a Q wave, an R wave and an S wave
➤ Non- Pathological Q waves may present in I,III,aVL,V5,V6
➤ R wave in lead V6 is smaller than V5
➤ Depth of S wave should not exceed 30mm
➤ Pathological Q wave >2mm deep and >1 mm wide or >25% amplitude of
the subsequent R wave
39. THE PR INTERVAL
➤ Atrial depolarisation and delay in AV junction (AV node/Bundle
of His)
➤ PR interval should be 120 to 200 milliseconds or 3 to 5 small
squares
➤ Less than 120 ms suggests pre-excitation
➤ Prolongation of the PR interval above 0.2 sec is called first -
degree heart block or AV delay
40. ST SEGMENT
➤ End of QRS complex to the beginning of the T wave
➤ Represents the beginning of ventricular repolarisation
➤ ST Segment is flat (isoelectric)
➤ Elevation or depression of ST segment by 1mm or more is abnormal
➤ “ J” (Junction) point is the point between QRS and ST segment
41. Morphology of elevated ST segment in MI
➤ Acute STEMI may produce ST elevation with either convex,concave
or oblique straight morphology
43. T WAVE
➤ Normal T wave is asymmetrical,first half having a gradual slope than
the second
➤ Should be at least 1/8 but less than 2/3 of the amplitude of the R
➤ T wave amplitude rarely exceeds 10 mm
➤ Abnormal T waves are symmetrical,tall,peaked,biphasic or inverted
➤ T wave follows the direction of the QRS deflection
44. QT INTERVAL
➤ Total duration of Depolarisation and repolarisation of ventricles
➤ QT interval decreases when heart rate increases
➤ QT interval should be 0.33-0.45 sec
➤ Should not be more than half of the interval between adjacent R
waves(R-R interval)
➤ QT interval should be measured in the ECG lead that shows the longest
intervals
➤ As it is rate dependent ,rate corrected QT or QTc interval index is used
➤ Bazett formula is commonly used- QTc = QT/square root of RR
45. U WAVE
➤ A small rounded deflection sometimes seen after the T wave
➤ It’s exact significance is not known
➤ Functionally,U waves represent the last phase of ventricular
repolarisation
➤ Prominent U waves are characteristic of hypokalemia
➤ Very prominent U wave also seen in patients taking so
talon,Phenothiazines or sometimes after cerebrovascular accident
46. Osborn wave(J wave)
➤ It is a positive deflection at J point (negative in aVR and V1)
➤ Characteristically seen in hypothermia
47. DELTA WAVE
➤ Delta wave is a slurred upstroke in the QRS complex often
associated with short PR interval.
➤ It is most commonly associated with pre-excitation syndrome
such as WPW.
➤ Short PR interval(<120ms)
➤ Broad QRS (>100ms)
➤ A slurred upstroke to the QRS complex(the delta wave)
48. Epsilon wave
➤ It is a small positive deflection buried in the end of QRS
complex
➤ Epsilon waves are caused by postexcitation of the myocytes in
the right ventricle
➤ Most characteristic finding in arrhythmogenic right ventricular
dysplasia(ARVD)
➤ Here myocytes are replaced with fat,producing islands of
myocytes in a sea of fat
➤ Best seen in ST segments of leads V1 and V2
49. NORMAL SINUS RHYTHM
➤ Every P wave must be followed by a QRS
➤ Normal duration of PR interval is 3-5 small squares
➤ The P wave is upright in leads I and II
50. SINUS BRADYCARDIA
➤ Sinus Rhythm with a resting heart rate of < 60bpm in adults
➤ Each P wave is followed by QRS
➤ Heart rate =50/min
52. with very fast heart rates the P waves may be hidden in the preceeding T wave,
producing a “CAMEL HUMP” appearance
53. SINUS PAUSE
➤ In diseases (eg- sick sinus syndrome) the SA node can fail in its
function.
➤ If failure is brief and recovery is prompt,the result is only a missed
beat(sinus pause)
➤ If recovery is delayed and no other focus assumes pacing
function,cardiac arrest follows
54. ATRIAL FIBRILLATION
➤ AF is the most common sustained arrhythmia. Characterized by
disorganized atrial electrical activity and contraction
➤ Irregularly irregular rhythm
➤ No P waves
➤ Absence of an isoelectric baseline
➤ Variable ventricular rate
➤ QRS complex usually <120 ms
➤ Fibrillatory waves may be present and can be either fine (amplitude
<0.5mm) or coarse (amplitude >0.5 mm)
➤ Fibrillatory waves may mimic P waves leading to misdiagnosis
56. Atrial Flutter
General features
➤ Narrow complex tachycardia
➤ Regular atrial activity at approx. 300 bpm
➤ Flutter waves (saw tooth pattern) bst seen in leads II,III,aVF-may be
more easily spotted by turning the ECG upside down
➤ Flutter waves in V1 may resemble P waves
➤ Loss of the isoelectric baseline
58. ATRIAL FLUTTER
➤ Rate A: 300/min ; V: 150/min
➤ Rhythm: irregular
➤ Axis : Normal
➤ P wave : Absent,replaced by flutter wave
➤ P-R interval : -
➤ QRS complex : varying
➤ S-T : Normal
➤ T : Upright
➤ Q-T : -
➤ U wave: Absent
➤ Conclusion : Atrial flutter with varying block
59. Accelerated Junctional Rhythm(AJR)
➤ AJR occurs when the rate of an AV junctional pacemaker exceeds
that of sinus node
➤ Narrow complex rhythm; QRS duration < 120 ms
➤ Ventricular rate usually 60-100 bpm
➤ Retrograde P waves may be present and can appear before,during or
after the QRS complex
➤ Retrograde P waves are usually inverted in the inferior
leads(II,III,aVF),upright in aVR + V1
➤ AV dissociation may be present with the ventricular rate usually
greater than the atrial rate
60.
61. VENTRICULAR FIBRILLATION
➤ Typical rhythm strip of ventricular fibrillation
➤ Chaotic irregular deflections of varying amplitude
➤ No identifiable P waves,QRS complexes, or T waves
➤ Rate 150 to 500 bpm
➤ Amplitude decreases with duration
62. ➤ A severely abnormal heart rhythm (arrhythmia) that can be life
threatening
➤ Emergency- requires advanced life support
➤ Most important shockable cardiac arrest rhythm
➤ Rate can not be discerned,rhythm unorganized
63. VENTRICULAR TACHYCARDIA
➤ Ventricular tachycardia (VT) is a broad complex tachycardia
originating in the ventricles
➤ There are several different types of VT-the most common being
Monomorphic VT
➤ Fast heart rhythm, that originates in one of the ventricles
➤ Potentially life threatening arrhythmia because it may lead to
ventricular fibrillation,asystole and sudden death
➤ Rate 100-250bpm
64. Features Suggestive of VT
➤ Very broad QRS complexes(>160ms)
➤ Absence of typical RBBBor LBBB morphology
➤ Extreme axis deviation-Northwest
➤ AV dissosciation
➤ Capture beats- occur when the sinoatrial node transiently captures
the ventricles,in the midst of AV dissociation,to produce a normal
QRS
➤ Fusion beats – occur when a sinus and ventricular beat coincide to
produce a hybrid complex of intermediate morphology
➤ Positive or negative concordance through out the leads –i.e.V1-6
shows entire positive (R) or entire negative (QS) complexes
65. ➤ Brugada’s sign- The distance from the onset of the QRS complex to
the nadir of the S wave is> 100ms
➤ Josephson’s sign-Notching near the nadir of the S-wave
➤ RSR’ complex with a taller “left rabbit ear”.This is the most specific
finding in favour of VT. This is in contrast to RBBB,where the right
rabbit ear is taller
66. TORSADES DE POINTES
➤ Polymorphic ventricular tachycardia characterised by a gradual change
in the amplitude and twisting of the QRS complexes around the
isoelectric line .
➤ Rate can not be determined
67. ECG motion Artefacts
➤ Motion artefact due to tremor or shivering can obscure the
waveforms of the ECG or simulate pathology,making ECG
interpretation difficult
➤ In certain circumstances (e.g –hypothermia),the presence of
shivering artefact may actually aid diagnosis
68. Referrences
➤ Leo Schamroth,An Introduction to Electrocardiography,Eighth
adapted edition
➤ Goldbergs clinical electrocardiography,8th edition
➤ www.litfl.com
