ECG interpretation

1. ECG INTERPRETATION
Dr. P.S.INDURKAR
professor in Anesthesia,
DY Patil Medical college, Mauritius

2. ECG
This short course reviews
• the main features of ECG tracings.
• A method for analyzing ECGs .
• assessment of rhythm, calculating heart rate
• observing P-wave forms, measurement of ECG
intervals and segments
• and the evaluation of other relevant waves.

3. Leads
The 12 leads on the ECG (I, II, III, aVL , aVF, aVR, V1 - 6) are
formed using only 9 electrodes (and a neutral)?
• Lead I is formed using the right arm electrode (red) as the
negative electrode and the left arm (yellow) electrode as the
positive.
• Lead II is formed using the right arm electrode (red) as the
negative electrode and the left leg electrode as the positive.
• Lead III is formed using the left arm electrode as the negative
electrode and the left leg electrode as the positive.
• aVL, aVF and aVR are composite leads, using the information
from the other leads .also known as augmented leads. They
are derived from the same three electrodes as leads I, II, and
III. However, they view the heart from different
angles(Einthoven,s law, Einthoven,s triangle)

4. Each lead can be thought of as looking at an area of myocardium
Limb leads look at the heart in the coronal plane
• aVL, , I and II = lateral
• II, III and aVF = inferior
• aVR = right side of the heart
Chest leads
• V1 to V6 look at the heart on the transverse plain
• V1 and V2 look at the anterior of the heart and R ventricle
• V3 and V4 = anterior and septal
• V5 and V6 = lateral and left ventricle

5. • ECG tracings are recorded on grid paper. The horizontal axis of
the ECG paper records time, with black marks at the top
indicating 3 second intervals.
• Each second is marked by 5 large grid blocks. Thus each large
blocks equals 0.2 second. The vertical axis records ECG
amplitude (voltage). Two large blocks equal 1 millivolt (mV).
Each small block equals 0.1 mV.
Within the large blocks are 5 small blocks, each representing
0.04 seconds
• 1mm (small square) = 0.04 sec
• 5mm (big square) = 0.2 sec

7. • Normal ECG tracings consist of waveform
components which indicate electrical events during
one heart beat. These waveforms are labeled P, Q, R,
S, T and U. (The following descriptions are with
respect to Lead II).
• P wave is the first deflection and is normally a
positive (upward) waveform. It indicates atrial
depolarization (Contraction).

8. • QRS complex follows the P wave. It normally begins
with a downward deflection Q; a larger upwards
deflection R; and then a downwards S wave.
• The QRS complex represents ventricular depolarization
and contraction.
• T wave is normally a modest upwards waveform,
representing ventricular repolarization.
• U wave indicates the recovery of the Purkinje
conduction fibers. This wave component may not be
observable.

10. ECG interpretation should be performed using a
standard procedure. For this course, we are
using an eight step procedure:
1) Rhythm 5) QRS Interval
2) Rate 6) T Wave
3) P Wave 7) QT Interval
4) PR Interval 8) ST Segment

11. RHYTHM
• Sinus Rhythm
Definition--Cardiac impulse originates from the sinus
node. Every QRS must be preceded by a P wave.
• Sinus bradycardia
Rhythm originates in the sinus node . Rate of less
than 60 beats per minute
• Sinus tachycardia
Rhythm originates in the sinus node. Rate of greater
than 100 beats per minute

12. RHYTHM
Rhythm means---are the heartbeats regular, meaning
that each heart beat's R-R interval is equal. Small
variations of up to 10% are considered equal.
Is the rhythm (R-R intervals) regularly irregular or
completely irregular? For example is there a pattern,
such as increasing R-R durations?
For ventricular rhythm, examine the R to R intervals on
the ECG strip. Calipers or paper marks can be used to
fix the distance for one R-R interval and then this
distance can be compared to other R-R pairs.

14. Is the rhythm regular?
• The easiest way to tell is to take a sheet of paper and
line up one edge with the tips of the R waves on the
rhythm strip.
• Mark off on the paper the positions of 3 or 4 R wave
tips
• Move the paper along the rhythm strip so that your
first mark lines up with another R wave tip
• See if the subsequent R wave tips line up with the
subsequent marks on your paper
• If they do line up, the rhythm is regular. If not, the
rhythm is irregular

15. RATE
There are several methods for determining heart rate.
1) Count the number of QRS complexes over a 6 second
interval. Multiply by 10 to determine heart rate. This method
works well for both regular and irregular rhythms.
In this image , we can count 7 QRS complexes, so the heart rate
is 70.

16. 2)The second method uses small boxes. Count the number of
small boxes for a typical R-R interval. Divide this number into
1500 to determine heart rate. In the above image, the number of
small boxes for the R-R interval is 22.5. The heart rate is
1500/21.5, which is 69.8.
3)Count the number of large squares between R waves i. e. the
RR interval in large squares .
• Rate = 300 /RR
• e. g. RR = 4 large squares , 300/ 4= 75 beats per minute

17. P-wave
The P wave represents atrial depolarization. In
normal ECGs, the P-wave precedes the QRS
complex. It looks like a small bump upwards from
the baseline. The amplitude is normally 0.05 to
0.25mV (0.5 to 2.5 small boxes). Normal duration
is 0.06-0.11 seconds (1.5 to 2.75 small boxes). The
shape of a P-wave is usually smooth and rounded.

18. P-wave assessment
Are they present?
Do they occur regularly?
Is there one P-wave for each QRS complex?
Are the P-Waves smooth, rounded, and upright?
Do all P-Waves have similar shapes?

19. PR Interval
• The PR Interval indicates AV conduction time.
It is measured from where the P wave begins
until the beginning of the QRS complex.
Calipers, marked paper or counting small
boxes methods can be used to determine PR
Intervals. Normally this interval is 0.12 to 0.20
seconds (3 to 5 small boxes) in adults, longer
in elderly people.
• This interval shortens with increased heart
rate.

20. PR Interval
• Also evaluate if PR Intervals are constant or varying across the
ECG strip. If they vary, determine if the variations are a steady
lengthening until the point where an expected QRS does not
appear.
PR Interval assessment while reading ECG:
1) Does the PR-Interval fall within the norm of 0.12-0.20
seconds?
2) Is the PR-Interval constant across the ECG tracing?

21. QRS complex
• The QRS complex indicates ventricular depolarization.
Depolarization triggers contraction of the ventricles.
Because of the larger tissue mass, the QRS complex is bigger
than the P wave. A typical QRS complex consists of three wave
components, one or two of these components may be
missing.
Measure the QRS interval from the end of the PR interval to
the end of the S wave. Use calipers, marking paper or by
counting small boxes. Normally this interval is 0.06 to 0.12
seconds (1.5 to 3 boxes).

22. • QRS assessment:
1) Does the QRS interval fall within the range of 0.08-
0.12 seconds?
2) Are the QRS complexes similar in appearance
across the ECG tracing?

23. T wave
• The T wave indicates the repolarization of the ventricles. It is a
slightly asymmetrical waveform which follows (after a pause),
the QRS complex. (Take note of T waves which have a
downward (negative) deflection or of T waves with tall,
pointed peaks.

24. T wave abnormalities
• Hyper acute T waves
• Inverted T waves
• Biphasic T waves-Causes-MI, Hypokalemia
• ͚Caŵel Huŵp͛ T waves--There are two causes:
1)Prominent U waves fused to the end of the T
wave, as seen in severe hypokalemia
2)Hidden P waves embedded in the T wave, as
seen in sinus tachycardia and various types of heart
block
• Flattened T waves-----it may indicate hypokalemia

25. • Peaked T waves
• Tall, narrow, symmetrically peaked T-waves are
characteristically seen in hyperkalaemia.
• Hyperacute T waves
• Broad, asLJŵŵetriĐallLJ peaked or ͚hLJperaĐute͛ T-waves
are seen in the early stages of ST-elevation MI
(STEMI) and often precede the appearance of ST
elevation and Q waves. They are also seen with
Prinzmetal angina.

26. Inverted T waves are seen in the following conditions:
• Normal finding in children
• Persistent juvenile T wave pattern
• Myocardial ischemia and infarction
• Bundle branch block
• VeŶtriĐular hLJpertrophLJ ;͚straiŶ͛ patterŶsͿ
• Pulmonary embolism
• Hypertrophic cardiomyopathy
• Raised intracranial pressure
Inferior T wave inversion due to acute ischaemia

27. Inferior T wave inversion with Q waves due to prior inferior MI

28. U-wave
• The U-wave is a small upright, rounded bump.
• U waves occur after the T wave and are often
difficult to see. They are thought to be due to
repolarization of the atrial septum
• Prominent U waves can be a sign of
hypokalemia , hyperthyroidism

29. QT interval
• The QT interval represents the time of ventricular
activity including both depolarization and
repolarization.
• It is measured from the beginning of the QRS
complex to the end of the T wave. Normally, the QT
interval is 0.36 to 0.44 seconds (9-11 boxes). The QT
interval will vary with patient gender, age and heart
rate. Another guideline is that normal QT Intervals is
less than half of the R-R Interval for heart rates
below 100 bpm.

30. QT interval

31. ST segment
• The ST segment represents the early part of
ventricular repolarization.
• The ST segment is from the end of the QRS complex
to beginning of the T wave. Normally the ST segment
is flat, being neither positive or negative relative to
the baseline. The most important cause of ST
segment abnormality (elevation or depression) is
myocardial ischemia or infarction

32. Exercise--Calculate the Heart rate

33. Calculate the Heart rhythm

34. P Wave shape varies

35. PR Interval varies

36. Wide QRS Interval

37. • Interpretation (adults)
• 60–100 beats/min
– Normal
• >100 beats/min
– Tachycardia
• <60 beats/min
– Bradycardia

38. • Normal Heart Rates in Children
• Newborn: 110 – 150 bpm
• 2 years: 85 – 125 bpm
• 4 years: 75 – 115 bpm
• 6 years+: 60 – 100 bpm

40. Axis deviation
Definition
• the mean direction of electrical forces in the frontal plane ( limb leads) as
measured from the zero reference point (lead 1)
• Normal values
– P wave: 0 to 75 degrees
– QRS complex: -30 to 90 degress
– T wave: QRS-T angle <45 degrees frontal or <60 degrees precordial

41. Axis deviation
• The simplest method of identifying gross deviations
in axis is to look at the QRS complexes in leads I and
aVF. Lead I is a left-sided lead, and as aVF is
perpendicular to lead I, it can be considered a right-sided
lead.
– Both leads I and aVF have mainly positive QRS
complexes = normal axis.
– Lead I is positive and aVF is negative = left axis
deviation (LAD).
– Lead I is negative and aVF is positive = right axis
deviation (RAD).
– Both leads negative = edžtreŵe ‘AD or ͞North-
West͟ adžis

42. Axis in the normal range
Lead aVF is the isoelectric lead.
•The tǁo perpeŶdiĐulars to aVF are 0° and
180°.
•Lead I is positiǀe ;i.e., orieŶted to the leftͿ.
•Therefore, the adžis has to ďe Ϭ°.

43. Axis in the left axis deviation (LAD) range
Lead aVR is the smallest and isoelectric lead.
•The tǁo perpeŶdiĐulars are -60° and +120°.
•Leads II aŶd III are ŵostlLJ Ŷegatiǀe ;i.e.,
moving away from the + left leg)
•The adžis, therefore, is -60°.

44. Axis in the right axis deviation (RAD) range
ead aVR is closest to being isoelectric
(slightly more positive than negative)
•The tǁo perpeŶdiĐulars are -60° and
+120°
•Lead I is ŵostlLJ Ŷegatiǀe; lead III is ŵostlLJ
positive.
•Therefore the adžis is Đlose to +ϭϮϬ°.
Because aVR is slightly more positive, the
axis is slightly beyond +120° (i.e., closer to
the positive right arm for aVR).

45. Right Axis Deviation (RAD)
Differential diagnosis
• Right Ventricular Hypertrophy (RVH) — most common
• Left Posterior Fascicular Block (LPFB) — diagnosis of exclusion
• Lateral and apical MI
• Acute Right Heart Strain, e.g. acute lung disease such as
pulmonary embolus
• Chronic lung disease, e.g. COPD
• Dextrocardia
• Ventricular pre-excitation (WPW) — LV free wall accessory
pathway
• Ventricular ectopy
• Hyperkalemia
• Sodium-channel blockade, e.g. tricyclic toxicity
• Secundum ASD — rSR͛ patterŶ
• Normal in infants and children
• Normal young or slender adults with a horizontally positioned
heart can also demonstrate a rightward QRS axis on the ECG.

46. Left Axis Deviation (LAD)
Differential diagnosis
• Left ventricular hypertrophy (LVH)
• Left Anterior Fascicular Block (LAFB) —
diagnosis of exclusion
• LBBB
• inferior MI
• ventricular ectopy
• paced beats
• Ventricular pre-excitation (WPW)
• Primum ASD — rSR͛ patterŶ

47. • Extreme Axis Deviation
– 180 to -90 degrees
• rare
Differential diagnosis
• Right Ventricular Hypertrophy (RVH)
• Apical MI
• VT
• Hyperkalemia

48. Axis Deviation
Wolff--Parkinson --White syndrome can cause
both Left and Right axis deviation
short PR interval, less than 3 small squares
(120 ms)
slurred upstroke to the QRS indicating pre-excitation
(delta wave)
broad QRS
secondary ST and T wave changes

49. Classic Wolff-Parkinson-White electrocardiogram with short PR, QRS >120 ms,
and delta wave

50. Heart block
• Conduction system

51. Heart block
• Sino-Atrial Exit Block
• Atrio-Ventricular (AV) Block
– 1st Degree AV Block
– 2nd Degree AV Block :Type I (Wenckebach)
– 2nd Degree AV Block: Type II (Mobitz)
– Complete (3rd Degree) AV Block
– AV Dissociation
• Intraventricular Blocks
– Right Bundle Branch Block
– Left Bundle Branch Block
– Left Anterior Fascicular Block
– Left Posterior Fascicular Block
– Bifascicular Blocks
– Nonspecific Intraventricular Block
– Wolff-Parkinson-White Preexcitation

53. Types of Heart Block
• First-degree heart block – The electrical impulses are slowed
as they pass through the conduction system, but they all
successfully reach the ventricles. First-degree heart
block rarely causes symptoms or problems. Well-trained
athletes may have first-degree heart block. Medications can
also cause this condition. No treatment is generally needed
for first-degree heart block.
• Second-degree heart block (Type I) – The electrical impulses
are delayed further and further with each heartbeat until a
beat fails to reach to the ventricles entirely. It sometimes
causes dizziness and/or other symptoms. People with normal
conduction systems may sometimes have type 1 second
degree heart block when they sleep.

54. • Second-degree heart block (Type II) – With this condition,
some of the electrical impulses are unable to reach the
ventricles. This condition is less common than Type I, and is
more serious. Usually, a pacemaker recommend to treat type II
second degree heart block, as it frequently progresses to third
degree heart block.
• Third-degree heart block – With this condition, also called
complete heart block, none of the electrical impulses from the
atria reach the ventricles. When the ventricles do not receive
electrical impulses from the atria, they may generate some
impulses on their own, called junctional or ventricular escape
ďeats. VeŶtriĐular esĐape ďeats, the heart͛s ŶaturallLJ oĐĐurriŶg
backups, are usually very slow.
• Patients C/O -Light headedness or dizziness, Palpitations,
Fatigue, Chest pressure or pain, Shortness of breath, Fainting
spells

55. • Bundle Branch Block – With this condition, the electrical impulses are slowed or
blocked as they travel through the specialized conducting tissue in one of the two
ventricles.
• Types of bundle branch blocks-Depending on the anatomical location of the
defect:
1)Right bundle branch block
2)Left Bundle branch block
The left bundle branch block can be further sub classified into:
a)Left anterior fascicular block. In this case only the anterior half of the left
bundle branch (fascicle) is involved
b)Left posterior fascicular block. Only the posterior part of the left bundle branch
is involved
Other classifications of bundle branch blocks are;
Bifascicular block--This is a combination of right bundle branch block (RBBB) and
either left anterior fascicular block (LAFB) or left posterior fascicular block (LPFB)
Trifascicular block--This is a combination of right bundle branch block with either
left anterior fascicular block or left posterior fascicular block together with a first
degree AV block.
Read more: http://www.hrsonline.org/Patient-Resources/Heart-Diseases-Disorders/Heart-Block#ixzz3EgcjiMKI

56. Symptoms of Heart Block
• Some people with heart block will not experience any symptoms. Others
will have symptoms that may include the following:
• Fainting ( syncope)
• Dizziness Lightheadedness
• Chest pain
• Shortness of breath
Risk factors for Heart Block
• Some medical conditions increase the risk for developing heart block.
These medical conditions include:
• Heart failure
• Prior heart attack
• Heart valve abnormalities
• Heart valve surgery
• Some medications or exposure to toxic substances
• Lyme disease
• Aging
Read more: http://www.hrsonline.org/Patient-Resources/Heart-Diseases-Disorders/Heart-Block#ixzz3Egd0vug3

57. LBBB
• ƒ If left bundle branch block is present, the QRS
Đoŵpledž ŵaLJ look like a ͚͚W͛͛ iŶ Vϭ aŶd/or aŶ
͚͚M͛͛shape iŶ V6.
•ƒ (New onset LBBB with chest pain consider Myocardial infarction. Not possible to
interpret the ST segment)

58. RBBB
It is also called RSR pattern . If right bundle
branch block is present, there may be an
͚M͛ iŶ Vϭ aŶd/ or a ͚W͛ iŶ V6.
Can occur in healthy people with normal QRS
width--partial RBBB

59. Myocardial infarction
• The leads affected determine the site of the
infarct.
• Inferior--II, III, aVF.
• Anteroseptal--V1-V4
• Anterolateral--V4 V6, I, aVL
• Posterior--Tall ǁide ‘ aŶd “T↓ iŶ Vϭ aŶd VϮ

60. Myocardial infarction
• Within hours: T wave may become peaked, ST
segment may begin to rise
• Within 24 hours: T wave inverts (may or may
not persist) ST elevation may persist
• Within a few days: pathological Q waves can
form and usually persists.

61. Inferior MI

62. Supraventricular tachycardias
These are tachycardias where the impulse is
initiated in the atria ( sinoatrial node, atrial wall
or atrioventricular node)
• If there is a normal conduction pathway when
the impulse reaches the ventricles, a narrow
QRS complex is formed, hence they are
narrow complex tachycardias However if there
is a conduction problem in the ventricles such
as LBBB, then a broad QRS complex is formed.
This would result in a form of broad complex
tachycardia

64. Atrial Fibrillation
• Features: There may be tachycardia The
rhythm is usually irregularly irregular.
• No P waves are discernible
• instead there is a shaky baseline This is
because there is no order to atrial
depolarization, different areas of atrium
depolarise at will

65. Atrial Fibrillation

66. Symptoms of AF
• Palpitation
• Shortness of breath
• Weakness
• Chest pain
• Dizziness or fainting
• Fatigue
• Confusion

67. Causes of AF
• High blood pressure is th e most common cause.
• ischemic heart disease.
• Other conditions and situations that may trigger
AF to develop include:
– An overactive thyroid gland (hyperthyroidism)
– Pneumonia
– Pulmonary embolus
– Obesity
– Lung cancer
– Drinking a lot of alcohol.
– Drinking a lot of caffeine (tea, coffee, etc).
• AF occurs in some people with heart valve
problems, pericardial disease, dilated cardiomyopathy
and hypertrophic cardiomyopathy

68. Atrial Fibrillation

69. Atrial flutter
There is a saw-tooth baseline which rises above and
dips below the isoelectric line. Atrial rate 250/ min
This is created by circular circuits of depolarisation
set up in the atria

70. Premature ventricular complex/contractions
Definition--A premature beat arising from an
ectopic focus within the ventricles.
Features:
• Broad QRS complex ;≥ 120 ms) with abnormal
morphology & Premature i.e. occurs earlier than
would be expected for the next sinus impulse.
• Variable ST segment and T wave changes.
• Usually followed by a full compensatory pause.
(Retrograde capture of the atria may or may not
occur).

71. PVCs may be either:
• Unifocal --Arising from a single ectopic focus;
each PVC is identical.
• Multifocal --Arising from two or more ectopic
foci; multiple QRS morphologies.
PVCs often occur in repeating patterns:
1. Bigeminy — every other beat is a PVC.
2. Trigeminy — every third beat is a PVC.
3. Quadrigeminy — every fourth beat is a PVC.
4. Couplet — two consecutive PVCs.
5. Triplet — three consecutive PVCs.

72. Causes
• Anxiety
• Sympathomimetics
• Beta-agonists
• Excess caffeine
• Hypokalaemia
• Hypomagnesaemia
• Digoxin toxicity
• Myocardial ischemia

73. Ventricular Tachycardia
• QRS complexes are wide and irregular in
shape. Usually secondary to infarction.
Circuits of depolarisation are set up in
damaged myocardium This leads to recurrent
early repolarisation of the ventricle leading to
tachycardia.
• As the rhythm originates in the ventricles,
there is a broad QRS complex Hence it is one
of the causes of a broad complex tachycardia
• Need to differentiate with supraventricular
tachycardia with aberrant conduction

74. Ventricular Tachycardia

75. Ventricular Fibrillation
• Completely disordered ventricular
depolarisation
• Not compatible with a cardiac output
• Results in a completely irregular trace
consisting of broad QRS complexes of varying
widths, heights and rates

76. References
1. www.thh.nhs.uk
2. www.practicalclinicalskills.com
3. ecg.utah.edu
4. cdn.lifeinthefastlane.com
5. www.ecglibrary.com
6. emedicine.mediscape.com
7. www.nhlbi.nih.gov
8. www.hrsonline.org
9. www.mayoclinic.org

77. Thank you