Electrical Activity of
By dr shazia askari
• ECG is define as ‘’ recording of electrical activity of
heart on a graph paper.’’
• Graphical representation of electrical activity of
• The machine which is used to record the electrical
activity of heart is ELECTROCARDIOGRAPH.
• a) ECG machine.
• b) power lab.
• The graph on which this electrical activity is recorded
is called ELECTROCARDIOGRAM.
Significance of ECG.
• ECG gives information about rate and rhythm of
• The physical orientation of heart i.e axis.
• Its a diagnostic tool for various heart conditions like
hypertrophies , ischemia, infarction , arrhythmias
conduction problems and pace maker activity.
• ECG does not provide information about
• This is long role of paper ,composed of small
• One square is 1mm wide and 1 mm high.
• On ECG paper there are thick lines, between two
thick lines there are 5 small squares.
• The speed of ECG machine is 25 mm per second.
• The time internal of each small square can be
• 25 small sqrs are equal to 1 second.
• 1 small sqr is equal to 1/25 second.
• i.e 0.04 seconds.
• vertically the small square represent the amount of
• One small sqr represent the potential of 0.1 mv.
• 10 small squares represent the potential of 1 mv.
• leads are electrodes which record the
electrical potential of heart at different sites.
• There are 12 ECG leads.
a) 3 bipolar limb leads.
b) 3 augmented limb leads.(unipolar).
c) 6 chest leads.
Bipolar limb leads.
• Lead 1 = left arm + ve , right arm _
• Lead 2 = right arm _ ve ,left leg + ve..
• Lead 3 = left arm _ ve , left leg +ve.
Augmented limb leads.
• AVR attach to right arm..
• AVL attach to left arm.
• AVF attach to left foot.
• Einthoven s triangle is a diagrammatic
way of illustrating that the two arms
and left leg form the apices of triangle
surrounding the heart.
• It is an equilateral triangle.
Einthoven “s rule.
• Einthovens law states that if the
electrical potentials of two leads are
known at any instant ,the third can be
determine by simply summing the first
Base line : flat, straight and isoelectric line
Wave form :deviation or movement away
from base line may be upward or downward
Segment : A line between two waves
Interval : a wave form plus a segment this
shows time duration
Complex : combination of several wave form
• P Wave shows atrial depolarization..
• Its duration is 0.1 sec (2 and half small sqr) and
height is 2.5 mv (2 and half small sqr).
• Presence of p waves in ECG strip shows the sinus
Abnormalities of P wave.
P .pulmonale :- This is tall and peaked P wave in
lead 1 and lead 2 and 3 in right atrial hypertrophy.
P. mitrale ;_ It is biphasic or broad P wave seen in
left atrial hypertrophy.(mitral stenosis).
-. Best seen in lead 2.
• Inverted P wave :- may be present in .
• a) Normally in lead V 1 and V2..
• b) In dextro cardia.
• c) Incorrectly placed electrodes.
• QRS complex represent the ventricular
• its normal duration is about 0. 08 seconds.( less than
2 small sqr) and hight is about 5 to 20 small sqrs.
• It is a wide complex because it mask the atrial
• Q wave is first wave of this complex but often
• Q wave present the interventricular septal
• It is first wave in ECG with negative deflection.
• Q wave greater than 1/3 the height of the R wave,
greater than 0.04 sec are abnormal and may represent
the old infarction.
Low voltage QRS complex.
• when the height of R or S wave is not more than
5mm… it is seen in..
Thick chest wall.
Problem in ECG machine.
High voltage QRS complex.
• This is present in ventricular hypertrophies.
• The maximum voltage of QRS complex may be 35
mv(35 small square).
• V1 and V2 show high voltage QRS complex in right
ventricular hypertrophy.( s wave)
• V5 and V6 show such QRS complex in left
ventricular hypertrophy. (r wave)
• it represent the ventricular repolarization.
• It is repolarizing wave but shows the upward
deflection because the part depolarized in the last is
first to be repolarized,, that is base of heart
depolarized in the last but is first to be repolarized.
• T wave should not be more than one third of R
• T wave inversion represent ischemia of heart.
• Tall and peaked R wave is present in hyperkalemia.
• Flattened R waves in pericarditis and myocarditis.
• This is from beginning of P wave to the beginning
of Q wave.
• Its normal duration is from 0.12 to 0.2 sec..
• It represent the conduction time of impulse from SA
node to the ventricles and AV delay.
Prolong PR interval.
• Prolong PR interval shows delayed conduction from
SA to AV node….
In first degree heart , 2nd degree and complete heart
First degree heart block.
• A-V BLOCK, FIRST DEGREE
Atrio-ventricular conduction lengthened
• Interval is about 0.2 to 0.3 sec.
Second degree heart block.
• A-V BLOCK, SECOND DEGREE
Sudden dropped QRS-complex
• PR interval is about 0.4 sec.
3rd degree heart block.
• When there is AV block , atria continue to beat at
normal rhythem while new pace maker develops in
purkinjie system with a rate of 15 to 50 beats /min.
• With a sudden block purkinje system cannot take
over pace maker activity immediately ,it takes about
16 to 30 sec. during which ventricles fail to contract
and person faint.
• This delayed pickup of heart beat is called stokes
• Measured from beginning of Q to the
end of the T wave
. Its duration is about (10 small sqrs).
. it indicates total systolic time of ventricles.
• this segment present between S wave and T
• It represent the plateau phase.
• its duration is 0.04 sec .
• The exact point at which all parts of ventricles are
depolarized i.e at the just end of QRS comples and
just at the begining of ST segment.
• At the point potential of ECG is zero with no
current is flowing through heart.
• Elevation . Seen in recent MI and
• Depression. Seen in ischemia, digitalis
therapy and hypokalemia.
If an electrode is placed so that wave of
depolarization spreads toward the recording
electrode, the ECG records a positive
If wave of depolarization spreads away from
recording electrode, a negative (downward)
How to calculate heart rate.
heart rate define as the no of heart beats per
minute.it can be determine by ECG VIA TWO
Rule of 300
10 Second Rule
Rule of 300
Take the number of “big boxes” between
neighboring QRS complexes, and divide this
into 300. The result will be approximately
equal to the rate.
Although fast, this method only works for
Rule of 10 sec
As most EKGs record 10 seconds of rhythm per
page, one can simply count the number of
beats present on the EKG and multiply by 6 to
get the number of beats per 60 seconds.
This method works well for irregular rhythms
• This is checked by the intervals between two R
waves or two S waves.
• If the no of small or large sqs are equal between two
R or S waves,, the rhythm is said to be normal.
• If not the rhythm is said to be irregular.
• Irregular rhythm is called Arrythmias.
• When atrial rate is between 200 to 300 betas /min
• During atrial flutter AV node is not able to transmit
all the impulses to ventricles so ventricular rate is 1/3
or ¼ of atrial rate.
• P wave is like saw tooth.
• Present is IHD , rheumatic heart disease.
Impulses travel in regular and circular course in
atria – No interval between T and P.
• A totally irregular and rapid atrial rate in which there
is a contraction of only small portion of atrial
• P waves replace by irregular F waves , bcoz whole
atria is not contracting.
• QRS complex and T waves r normal but rhythm is
Impulses have random pathways in atria.
Impulse originate at ventricular pacemaker –
odd/wide QRS complex - often due to
myocardial infarction , rate is about 120/ to
• Rapid ,irregular and ineffective contractions
of small segments of ventricles is termed as
• Peripheral pulse is absent bcoz cardiac out
put is zero.
hapazerd ventricular depolarization – ineffective at
pumping – death within minutes
• The flow of current from one point to another is
representing by an arrow. This is called Vector.
• The direction of flow of current i.e the arrow
point is always towards the positive direction.
The range of cardiac axis is 0 to +90 degrees.
Beyond this limit it is said to be deviated.
By near-consensus, the normal QRS axis is defined as
ranging from -30° to +90°.
-30° to -90° is referred to as a left axis deviation (LAD)
+90° to +180° is referred to as a right axis deviation
• Deviation to R: increased activity in R vent. –
obstruction in lung, pulmonary emboli, some heart
• Deviation to L: increased activity in L vent. –
hypertension, aortic stenosis, ischemic heart disease