Ecg reading basic 2021 june 13

ECG
Basics
DR J P SONI
PROFESSOR AND HEAD OF THE DEPARTMENT
PAEDIATRICS
DIVISION OF PEDIATRIC CARDIOLOGY
DR S N MEDICAL COLLEGE
JODHPUR
doc_jpsoni@yahoo.com

How many tissue fibers are
there in Heart ?

Myocardial fibers
• MYOCARDIAL CONTRACTILE FIBERS –
• are Non-automatic in atria and ventricle.
• These are Na+ driven tissues, usually cannot generate own electric
impulse.

Pacemaker & conducting fibers
All of the cells in the heart have the ability to initiate an action potential.
However, only some of these cells are designed to routinely trigger heart beats. These cells are
found in the conduction system of the heart - the SA node, AV node, Bundle of His and Purkinje
fibers.

Conducting system
Automatic conducting fibers are Ca++ driven tissues and can generate
own impulse - PACEMAKER.
It consist of -
1.The nodal system- consists of two nodes –
- The sinoatrial node (also called the S-A node or the sinus node). Is
situated in right atrium close to svc.
-The atrioventricular node (also called the A-V node).

Conducting system
2. INTERNODAL CONDUCTING FIBERS
2. The internodal pathway:
AV node

Conducting system
CONDUCTING FIBERS
3. The Purkinje system
(also called the His-Purkinje system):
The atrioventricular bundle
(also called the A-V bundle or the
bundle of His).
The right and left bundle
branches.
The Purkinje fibers.

What is the automaticity of
SA,AV & ventricular system ?

The sinoatrial node is a single specialized node located in the right atrium;
which has a higher automaticity (a faster pacemaker) than the rest of the heart
and therefore is usually responsible for setting the heart rate and initiating each
heart beat.

What are the factors which
influences myocardial contractility?

FACTORS THAT INFLUENCE
MYOCARDIAL CONTRACTILITY
* Sympathetic stimulation has a +ve inotropic effect
* Parasympathetic stimulation has a –ve inotropic effect on the atrial myocardium
only because the vagus nerves enervation is upto atria.
* The preload (EDV): -
* Heart rate: -

•Sympathetic stimulation has a +ve inotropic effect on both atria
and ventricle.
• Activation of β1 receptors
• Augmentation of L-type Ca2+ current
• Phase 4 AP more steeper

Current always flow from negative to positive direction.
When Lead is parallel to the vector, that lead will have Positive deflection
When lead is perpendicular to the vector, that lead will have no deflection or Negative or biphasic
deflection

ECG LEAD NEONATAL
(NON - TRAUMATIC LEADS)
Standard Limb Leads :
Lead I
Lead II
Lead III
Augmented limb leads
aVR
aVL
aVF
Chest leads : V1 to V6

ECG LEAD - INFANCY
Einthoven's triangle is an imaginary formation
of three limb leads in a triangle used in
electrocardiography, formed by the two
shoulders and the pubis. The shape forms an
inverted equilateral triangle with the heart at
the center. It is named after Willem Einthoven
Einthoven's law:
That lead I + lead III = lead II
or
I+(-II)+III = 0
Thus, the deflection in one lead can be
predicted from the deflections in the other
two.

AUGMENTED ECG LEAD
aVR, aVL and aVF and V1-V6 leads are not unipolar, but bipolar leads, with the
indifferent pole carrying a very low negative potential.
aVR is recorded the GCT consists of a connection of left arm and left
leg; when aVL is recorded the GCT consists of a connection of right arm
and left leg; when aVF is recorded the GCT consists of a connection of
right arm and left arm.
Thus the GCT is variable, consisting of the mean of the potentials of
the 2 (different for the 3 recordings) limb leads, in contrast to the
WCT which is univariable.
This modification of Goldberger leads to the augmentation of the
recorded limb leads by 50%, as can be shown mathematically, and thus
the aVR, aVL, and aVF came into being.
RA
FF
LA
aVR aVL
aVF
+
+
_
_
_
_
+
+
+
+

SURFACE
ELECTRO-CARDIOGRAPHY
The hexaxial reference system is made up by
the six limb leads And provide information
about Supero-inferior and right –left
relationship of electromotive forces in frontal
plane.
The bipolar limb leads I,II & III are clockwise
With angle between them of 60 degree.
Positive inferiorly.
Augmented limb leads aVL positive at left
shoulder, aVF positive inferiorly at foot end
& aVR positive superiorly at right shoulder
The lead I and aVF at right angle at the
electric center

CHEST LEADS
The horizontal chest leads or precordial
leads V1-V6 ,V3R,V4R provide information
about antero-posterior (V2) and
Left to right ( V6) relationship.
V3R is mirror image of V3
V4R is mirror image of V4
R wave in V6 - left ward force
S wave in V6 – Right ward force
R wave in V1, V3R & V4R – right & anterior force
S wave in V1, V3r & V4R - left ward & posterior
force

Anatomical Relation of leads in a Standard 12 Lead ECG :-
Lead II , III & aVF :- View inferior surface of heart
Lead I & V4 :- View of the Anterior surface
Lead I, aVL, V5 & V6 :- View lateral surface
Lead V1 & aVR :- look through the Right atrium directly into the cavity of left
ventricle
. Leads V1 and V2 :- The QRS complexes are predominantly negative with small R waves and
relatively deep S waves because the more muscular left ventricle produces
depolarization current flowing away from these leads.

ECG paper : One large box have total 25 squares, with five vertical and horizontal lines.
In height 10 segments are equal to 1mm volt.
One segment in length is equal to time interval 0.04 sec and five segment are equal to 0.2 sec
Normal speed of ECG paper is 5 big segment per second.
If tachycardia, for better depiction ECG tracing, particularly “P” wave paper speed is
increase to 10 Big second per second
5x5 mm
10 seg = 1 mV

ECG paper : Height 10 segments are equal to 1mm volt and 5seg are equal to 0.5 mvolt
10 seg = 1 mV
1mV is for lead I,II.II, aVR, aVL aVF
0.5 mV is for chest leads
When chest leads volts is very high

ECG paper : Height 10 segments are equal to 1mm volt and 5seg are equal to 0.5 m volt
ECG is of normal voltage or half voltage
10 seg = 1 mV
1mV is for lead I,II.II, aVR, aVL aVF
0.5 mV is for chest leads
When chest leads volts is very high

Pre pericardiocentesis
Post pericardiocentesis

• Simple rule:
• 1500/number of small squares
• 300/number of large squares
• Rule of ten second : Take ECG for 10 sec,
• Count Heart rate for 10 sec and multiply by 6 will give
Heart rate per minute.

Rhythm is regular or irregular -
10 seg = 1 mV
ATRIAL FIBRILLATION -

10 seg = 1 mV
Negative “P” in aVR suggest heart Situs Solitus ( normal )
Positive “P” wave in aVR suggest abnormal situs – Situs Inversus or Ambiguous

10 seg = 1 mV
aVR Negative “P” wave

aVR - Positive “P” wave suggestive of
situs inversus

Abnormal “P” wave : positive in aVR, Negative in I,II,III,aVF

•Atrial depolarisation proceeds sequentially from right to left, with the right atrium activated before the
left atrium.
•The right and left atrial waveforms summate to form the P wave.
•The first 1/3 of the P wave corresponds to right atrial activation,
the final 1/3 corresponds to left atrial activation; the middle 1/3 is
a combination of the two.
•In most leads (e.g. lead II), the right and left atrial waveforms move in the same direction, forming a
monophasic P wave.
•However, in lead V1 the right and left atrial waveforms move in opposite directions. This produces a
biphasic P wave with the initial positive deflection corresponding to right atrial activation and the
subsequent negative deflection denoting left atrial activation.
•This separation of right and left atrial electrical forces in lead V1 means that abnormalities affecting each
individual atrial waveform can be discerned in this lead. Elsewhere, the overall shape of the P wave is used
to infer the atrial abnormality.
RA LA

The P wave is the first positive deflection on the ECG and represents atrial depolarisation
•The P wave is the first positive deflection on the ECG
•It represents atrial depolarisation
•Duration: < 0.12 s (<120ms or 3 small squares)
Morphology
•Smooth contour
•Monophasic in lead II
•Biphasic in V1
Axis
•Normal P wave axis is between 0° and +75°
•P waves should be upright in leads I and II, inverted in aVR
Duration
•< 0.12 s (<120ms or 3 small squares)
Amplitude
•< 2.5 mm (0.25mV) in the limb leads
•< 1.5 mm (0.15mV) in the precordial leads
“P” wave abnormalities are most easily seen in the inferior leads (II, III and aVF) and lead V1, as the P waves
are most prominent in these leads.

In NSR, the P wave is less than 120 milliseconds in duration and less than 0.15 mV to 0.25 mV in height
in lead II. The permissible maximum varies based on the lead. If there is a biphasic P wave in lead V1,
the terminal component should be less than 40 milliseconds in duration and 0.10 mV in depth.
The P wave should also have a normal axis (0 degrees to more than 90 degrees) and constant
morphology.
The normal axis is indicated by P waves that are:
1.upright in leads I, II, and often aVF
2. “P” wave Inverted in lead aVR, Positive “P” wave in aVR suggest situs inversus
3.Upright, inverted, or biphasic in leads III and aVL
4.Upright or biphasic in leads V1 and V2, “P” is positive in V1 if chest lead is placed UP
5.Upright in leads V3 through V6.

The location of “P” wave axis determine the origin of an atrial derived rhythm.
It is determined by measuring net positive or negative P-wave deflections on all six limb leads
and calculating the net direction of electrical activity using the hexaxial reference system.
Abnormal P-wave axis is defined as any value outside 0–75°
0 to 90 degree Normal sinus rhythm
90-180 degree Left axis deviation
180-270 degree low left axis deviation
270 to 0 degree low right axis deviation

R = +3 mm
R = +12 mm
Axis = 45
Normal
+I
-aVF

•In right atrial enlargement, right atrial depolarisation lasts longer than normal and its waveform
extends to the end of left atrial depolarisation.
•Although the amplitude of the right atrial depolarisation current remains unchanged, its peak now falls
on top of that of the left atrial depolarisation wave.
•The combination of these two waveforms produces a P waves that is taller than normal (> 2.5 mm),
although the width remains unchanged (< 120 ms).

In right atrial enlargement, right atrial depolarisation lasts longer than normal and its waveform extends to the
end of left atrial depolarisation, summation of both results in tall and peaked “P” wave , that is “P” pulmonale

•In left atrial enlargement, left atrial depolarisation lasts longer than normal but its amplitude remains unchanged.
•Therefore, the height of the resultant P wave remains within normal limits but its duration is longer than 120 ms.
•A notch (broken line) near its peak may or may not be present (“P mitrale”).

•A notch (broken line) near its peak may or may not be present (“P mitrale” “M” shape ).
•Ventricular inversion
•Both A-V attached to Left Atrium

P wave may be absent – Atrial fibrillation, SVT - AVNRT,
Negative “P” wave in I,
Wandering Atrial Pacemaker
WAP is not pathologic and is often seen in young, healthy individuals. It results from a change in the
dominant pacemaker focus from the sinus node to ectopic atrial foci.
There must be at least three dominant ectopic atrial foci to meet the diagnostic criteria for WAP.
This can be seen on ECG by a variation in P wave morphology and the PR interval. Each variation in P wave
morphology represents a different ectopic focus. The closer the ectopic focus is to the AV node, the
shorter the PR interval will be. Because WAP is not considered pathologic and often asymptomatic, there is
no indication for treatment. (WAP < 100 bpm, MAT ≥ 100 bpm)

•First degree: With first-degree SA nodal exit block, there is impulse exit slowing with normal 1:1
conduction. A body surface EKG is not able to recognize this.
•Second degree: Like second-degree AV nodal blocks, there are two types second-degree SA nodal exit
blocks –
• type I (Wenckebach) and type II.
•With type I (Wenckebach), the P-P intervals progressively shorten in duration until a dropped P wave
occurs. The dropped P wave results in a pause that is less than two P-P intervals in duration.
• While type II also has a pause from a dropped P wave, it is a multiple of the SA nodal pacemaker input.
Therefore, the P-P intervals should remain constant and compensatory in nature.
•Third-degree: With third-degree SA nodal exit block, the SA node impulse is unable to reach the right
atrium. Thus, the atrial will not depolarize, and there will be no P wave. For this reason, it cannot be
distinguished from sinus arrest.

Type II also has a pause from a dropped P wave

Subsidiary Atrial Pacemakers
Subsidiary atrial pacemakers have been identified in the atrial myocardium, especially in the crista
terminalis, at the junction of the inferior right atrium and inferior vena cava, near or on
the eustachian ridge, near the coronary sinus ostium, in the atrial muscle that extends into
the tricuspid and mitral valves, and in the muscle sleeves that extend into the cardiac veins (venae
cavae and pulmonary veins).

Age PR interval sec
0-1 day 0.08-0.16
1-3 days 0.08-0.14
3-7 days 0.08-0.14
7-30days 0.07-0.14
> 1 months 0.07-0.13

COMMON IRREGULAR NARROW QRS TACHYCARDIA
Ectopic atrial tachycardia with
variable conduction
Except the above 3 conditions, all other SVTs are regular
Atrial fibrillation- Variable conduction across
AV node.
extremely rare in infants
Atrial flutter – usually fixed
conduction

When the QRS complex is clearly positive, it means that the electric impulse flows towards the lead.
if the QRS complex is negative, the impulse flows away from the lead.
if the QRS complex is biphasic it means the direction of the impulse is perpendicular to the lead.
The most efficient way to estimate axis is to look at LEAD I and LEAD aVF.
Step I - Determine QRS – A positive or negative in Lead I that is in lead I net deflection R-S =
- Determine QRS - A positive or negative in Lead aVF that is lead aVF net deflection R-S =
Step II - Join both mark by perpendicular line to get final axis in degree.
QRS COMPLEX
I aVF AXIS
+ + NORMAL -30 TO +90
+ - LEFT AXIS -30 TO - 90
- + RIGHT AXIS +90 TO +180
- - RIGHT SUPERIOR AXIS
_90--180

The most efficient way to estimate axis is to look at LEAD I and LEAD aVF.
Step I - Determine QRS – A positive or negative in Lead I that is in lead I net deflection R-S =
- Determine QRS - A positive or negative in Lead aVF that is lead aVF net deflection R-S =
and determine the quadrant
Step II - Find out biphasic or equiphasic lead, axis is perpendicular to it, in determined quadrant .
QRS COMPLEX
I aVF AXIS
+ + NORMAL -30 TO +90
+ - LEFT AXIS -30 TO - 90
- + RIGHT AXIS +90 TO +180
- - RIGHT SUPERIOR AXIS
_90--180

AGE AXIS
0-1 DAY 60-120
1-3 DAY 64-197
3-7 DAYS 75-185
7-30 DAYS 65-160
1-3 MONTHS 31-115
Find out lead of maximum positive QRS
Than look for lead which perpendicular to it, what is difference between R-S; suppose 2 mm
Than axis is; axis of Maximum QRS -/+ 10degree per mm

R = +3 mm
R = +12 mm
Axis = 80
Normal
+I
-aVF

R = - 4 mm
R = +4 mm
Axis = +45
Normal
Pt. of small VSD
Normal axis
No hypertrophy
+I
-aVF
V1
V2
I= 7
aVf = 7

R = - 4 mm
R = +4 mm
Axis = + 165; RAD
+I
-aVF

Fusion beat
or
Capture beat
E C G

R = +3 mm
R = +12 mm
Axis = 80
Normal
- I
-aVF

Cyanotic CHD
I
II
III aVF
aVL
aVR V1
Left axis deviation with left ventricular hypertrophy - tricuspid atresia

Abnormal quadrant QRS axis - Double outlet right ventricle
Cyanotic CHD

I - R = -3 mm
aVF - R = - 5mm
Axis = - 135
+I
-aVF
- aVF

R = - 4 mm
R = +4 mm
Axis = 80
Normal
+I
-aVF
V1
V2
“P” Pulmonale
aVR = qR

“q” wave in III
“q” wave inV1 to V3, positive “T” wave in v1 to v6I
Ventricular inversion

R = - 4 mm
V6 S = -3 mm
Axis = + 125
+I
-aVF
V1= R 7, T upright
V2
I R = - 5
aVf = 4

R = - 4 mm
V6 S = -7 mm
Axis = + 125
RAD
aVR= qR
R 5+S 9
= 14
+I
-aVF
V1= equiphasic, T upright
II= P - Pulmonale
I R = - 5
aVF = +7
aVR = qR

The “T” wave axis is determined by the same method as used to determine the QRS axis.
In the normal newborn, children and adults the mean T axis is + 45 degree ( 0 to + 90 degree)
T wave must be upright in lead I and aVF.
The T wave axis outside normal quadrant is seen in
During the 1st day of life, right axis deviation, large “R” wave and upright T wave in right precordial
leads v3R,v4Rand V1. T wave become negative with in 72 hours of birth, if persist beyond 7 days
Suggestive of right ventricular strain.
Severe ventricular hypertrophy with strain
Ventricular conduction disturbance
Metabolic disorder – popmes disease

S POTASSIUM ECG CHANGES
2.5 ST seg depression
Round “T” wave
Prominent U wave
3.5 – 5.5 Normal
5.5- 6.5 Peaked Tall “T” Wave
Prolonged PR
6.5 -8 Loss of “P” wave
Wide QRS
ST seg. Elevation
Ectopic beat /escape rhythm
>8 Wide QRS, SIGN wave
VT
Asystole
Bundle branch block
Fascicular Block

Angle between QRS & T axis.
The median value for QRS-T angle was 20°, and the median
values for QRS-axis and T-axis were 40 and 30°, respectively.
QRS-T angle did not differ between genders, with a mean
QRS-T angle being 29° in men and women, or in different age
groups.
A QRS/T angle of ≥ 100 degrees is nothing more than a mathematical representation of a general pattern of
T-wave discordance. Generally speaking, it means the T-waves on the ECG are deflected opposite the majority
of the QRS complex, which is a normal finding in left bundle branch block, paced rhythm, and left ventricular
hypertrophy with strain.

The 'U' wave is a wave on an electrocardiogram (ECG). It comes after the T wave of ventricular
repolarization and may not always be observed as a result of its small size. 'U' waves are thought
to represent repolarization of the Purkinje fibers and IVS. It is observed in chest leads. Direction of U
wave is same as of T wave.
Prominent “U” wave
Hypokalaemia
Hypomagnesemia
Hypocalcaemia
Hypothermia
Digoxin
LVH OR HCM
Raised ICH

Left Ventricular Hypertrophy (LVH)
• Limb lead criteria –
Axis – LAD
• Augmented Limb-lead voltage criteria:
• R in aVL ≥ 11 mm or, if left axis deviation
• R in aVL ≥ 13 mm plus S in III ≥ 15 mm
• R in I + S in III > 25 mm
Cornell criteria: Add the R wave in aVL and the S wave in V3. If the sum is greater than 28 millimeters in
males or greater than 20 mm in females, LVH is present.
Modified Cornell Criteria: Examine the R wave in aVL. If the R wave is greater than 12 mm in amplitude, LVH
is present.
• Chest lead voltage criteria
Sokolow-Lyon Criteria: Add the S wave in V1 plus the R wave in V5 or V6. If the sum is greater than 35
mm, LVH is present.

General ECG features include:
• Leftward shift in frontal plane QRS axis
•≥ QRS amplitude (voltage criteria; i.e., tall R-waves in LV leads, deep S-waves in RV leads)
•Delayed intrinsicoid deflection in V6 (i.e., time from QRS onset to peak R is ≥ 0.05 sec)
(Intrinsicoid deflection: time between QRS complex onset & R wave peak (in leads that begin with R wave
& have no Q wave).The intrinsicoid deflection reflects the depolarization vector from the endocardium to
the epicardium.)
•Widened QRS/T angle (i.e., left ventricular strain pattern, or ST-T oriented opposite to QRS direction)
•Evidence for left atrial enlargement (LAE)

Left Ventricular Hypertrophy (LVH) - summarty
Limb lead criteria – LAD Left Axis Deviation
• R in aVL ≥ 11 mm , R in I, II, III, aVL, aVF
R in V1 + S in V5 or V6 ≥ 10 mm
• R/S ratio in V1 or V2 < 1
• R in V5 or V6 < 5 mm
• S in V1 or V2 > 7 mm
• Q wave in V5,V6
• T wave negative in lateral leads
•ST segment depression and T wave inversion in left precordial leads that is opposite to R wave deflection
• QRS-T Axis angle >100

+ECG Criteria Points
•Voltage Criteria (any of):
•R or S in limb leads ≥ 20 mm
•S in V1 or V2 ≥ 30 mm
•R in V5 or V6 ≥ 30 mm
3 points
•ST-T Abnormalities : Without digitalis
•ST-T abnormalities With digitalis
3 points
1 point
Left Atrial Enlargement in V1 3 points
Left axis deviation 2 points
QRS duration 0.09 sec 1 point
Delayed intrinsicoid deflection in V5 or V6 (>0.05 sec) 1 point
ESTES Criteria for LVH
("diagnostic", ≥ 5 points; "probable", 4 points)

R = - 4 mm
V6 S = +24 mm
Axis = - 30 LAD
aVL, aVF = R
SV1+RV6 = >35
+I
aVF aVL = R
V1= S 23
II= P - Pulmonale
I R = + 5
aVR = S
V6 - -T

Right Ventricular Hypertrophy (RVH)
Limb lead criteria – RAD Right Axis Deviation
• R in aVR ≥ 11 mm or qR in aVR
R in V1 + S in V5 or V6 ≥ 10 mm
•ST segment depression and T wave inversion in right precordial leads that is opposite to R wave deflection
•Upright “T” in v1, v2 after 3 days of life .

R = - 4 mm
R = +4 mm
Axis = 80
Normal
+I
-aVF
V1
V2
“P” Pulmonale
aVR = qR
V1= R wave, upright “T” wave in V1,2,3,
V6= “S”
RAD

Tall “T” Himalayan - Infant of diabetic mother
P Pulmonale

Specific ECG features RVH (assumes normal calibration of 1 mV = 10 mm):
•Any one or more of the following (if QRS duration < 0.12 sec):
• Right axis deviation (> 90 degrees) in presence of disease capable of causing RVH
• R in aVR ≥ 5 mm, or
• R in aVR > Q in aVR
•Any one of the following in chest lead V1:
• R/S ratio > 1 and negative T wave
• qR pattern
• R gt; 6 mm, or S < 2mm, or rSR' with R' > 10 mm
•Other chest lead criteria:
• R in V1 + S in V5 (or V6) 10 mm
•ST segment depression and T wave inversion in right precordial leads that is opposite to R wave
deflection

Biventricular Hypertrophy (difficult ECG diagnosis to make)
In the presence of LAE any one of the following suggests this diagnosis:
•R/S ratio in V5 or V6 < 1
•S in V5 or V6 > 6 mm
•RAD (> 90 degrees)
Other suggestive ECG findings:
•Criteria for LVH and RVH both met
•LVH criteria met and RAD or RAE present

The ECG criteria for a left bundle branch block include:
1.QRS duration greater than 120 milliseconds
2.Absence of Q wave in leads I, V5 and V6
3.Monomorphic R wave in I, V5 and V6
4.ST and T wave displacement opposite to the major deflection of the QRS complex
5.Dominant S wave in V1
6.Prolonged R wave peak time > 60ms in leads V5-6

Complete RBBB
1.QRS duration greater than or equal to 120 ms in adults, greater than 100 ms in children ages 4 to 16
years, and greater than 90 ms in children less than 4 years of age.
2.rsr′, rsR′, or rSR′ in leads V1 or V2. The R′ or r′ deflection is usually wider than the initial R wave. In a
minority of patients, a wide and often notched R wave pattern may be seen in lead V1 and/or V2.
3.S wave of greater duration than R wave or greater than 40 ms in leads I and V6 in adults.
4.Normal R peak time in leads V5 and V6 but greater than 50 ms in lead V1.

Morphologic alteration of the cardiac silhouette and levo position of the heart with an overlap of the right
cardiac border to the vertebral column (black arrows), increase of the aortic knob, and of the main
pulmonary artery convexity with interposition of lung tissue between them (*), and a band of lucency
between the heart and left hemidiaphragm is also seen (white arrow)
Absence of R-wave growth in precordial, and growth data of right cavities. In
addition, the presence of the phenomenon of swinging heart in right precordial

Echocardiographic investigation which was performed on the 1 st day of life, revealed
marked hypertrophy of RV free wall (8, 9 and 11 mm in diastole, respectively),
interventricular septum (7, 8 and 8.5 mm in diastole, respectively) and a small RV cavity
(1.85, 1.63 and 1.69 cm 2 in diastole, respectively)

Ecg reading basic 2021 june 13

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