ECG PART 1

Electrocardiography


The Electrocardiogram
the myocardium is a large mass of muscle undergoing
electrical changes at the same time

These generates a large changing electrical ?eld which can

be detected by electrodes on the body surface

this is the electrocardiogram


Limb lead


Limb lead lookingat heart
£1q (—1 50 ?)
aVL (-30 : )

/
||| (+1201) || (+603)
aVF (+909)

Figure 2. The: limb leads looldng at the: 1115:2111 in a VEITiCi-ll plane.


Chest lead


Chest lead looking at heart

V1 V2 V3 V4


Thebasic pattern of the ECG is
logical

- electrical activity towards a lead causes an upward
deflection
electrical activity away from a lead causes a
downward deflection
depolarization and repolarization deflections occur
in opposite directions.


theomplitude oitlie Signal depends on

° how much muscle is depolarising

° how directly towards the electrode the

excitation is moving


Depolarization of the heart

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Conduction over the heart
° activity starts at the SA

node

- depolarisation spreads
over the atria
° to the AV node
where there is a delay of C.
12.0 IDS


Spread from cell to cell
spread ofexcitation over the myocardium also
generates a changing signal which electrodes detect
- so the ECG is explained by a combination ofthe

effects of depolarisation and repolarisation and their
spread over the heart


Conduction over the heart
- after the delay, activity spreads down the septum

- and then out over the ventricular myocardium

- from the inside (endocardial) surface to the outside

(epicardial) surface

until all the ventricular cells are depolarised


Repolarisation
° after about 280 ms cells
begin to repolarise
- repolarisation spreads in
the opposite direction over
the ventricle to
depolarisation
epicardial surface
repolarises ?rst
- endocardial surface
repolarises last


The basic pattern of electrically-
activity across the heart

«(— PR +

interval

"i

R

.J point

T

A U

A

ST
segment

«(—?v

S

QRS

interval

QT h

interval

Figure 4. The basic pattern of eleetn eal activity aet‘ees the heart,


Sothat
P wave — atrial depolarisation
Q wave — septal depolarisation spreading to
ventricle
R wave — main ventricular depolarisation
S wave — end ventricular depolarisation
T wave — ventricular repolarisation


ECG paper

: 1 sec :]
3 sec | .04 sec t iOOOm sec!
: " ‘ : (40m sec} _‘
(200m sec: I 4] F — PAPER SPEED 25mm/sec
1*— R 0,-1-
ln re rm} mm:- mm

W

t

i

l

I

i

I

I

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lmV

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VERTICAL IS ma HSquare : I mm 0.] mV HORIZONTAL
I Large Square = 5mm (0.5mV)
AXIS AXIS
2 Large Squares : ImV

l Small Square = .04 sec {40 m sec}
I Large Square = .2 sec (200 m sec)
5 Large Squares: I sec {1000 m sec)


ECG Description& Interpretation
ECG should be read in two steps: description 81 then
interpretation.
The description of ECG should be performed in an
orderly fashion as follow :

1—Techn1calqua11ty 8-QRS complex

z—Rhythm

-St se ment

3—Rate 9 g
4—Cardiac axis lo-Twave
5-P ae 11-Qt interval

6—PR segment

12-Additional waves

7—PR interval


Technical quality -
Look at speed which should be 25mm/s &look then to
the amplitude which is normally lomm/s both these
data are provided in the ECG paper.
Then look to aVR lead ,normally the deflection is
downward
If its upward think about
1—reversed limb lead placement
2—dextrocardia
3—right ventricular hypertrophy /strain or RBBB


Rhythm
The rhythm could be either regular or not depending
on R—R interval.
Causes of irregular rhythm:
Sinus arrhythmia, frequent ectopic beats ,
Atrial ?brillation ,Atrial flutter, 2nd degree heart blook
with variable response


Atrial fibrill tion f(ine
(irregular tachycardia wit

tlli normal 81RS complex


HEART RATE
1—Regular rhythm
Heart rate=300/number of large squares between beats

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4-f,_.=" -‘_._.r-_l *‘M‘L? 300/3.1=97 BPM


2-lrregular rhythm
Heart rate=number of R wave in 15 large square *20

52.0: 100


Hegftrate above loO-eaJ led tachycardia ;rate below—" 60
called bradycardia

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Cardiac axis

The axis of ECG is the major direction of overall
electrical activity of the heart .
It could be normal ,left axis deviation or right axis

deviation.


Deflection of depolarization
The average deflection of depolarization wave in the
ventricle spread from 11 o clock to 5 o clock. Its therefore
moving a way from aVR and toward other limb lead.

The direction of QRS complex in lead 1&aVF determine
cardiac axis


Positive
Positive
Negative
Negative

aVF
positive
Negative
Positive
Negative

Interpretation
Normal
left aXis deviation
Right aXis deviation
Extreme right aXis deviation


Calculation of electrical axis depending on QRS polarity
in leads I and aVF


causes:

Left AD: LVI-I, Left Anterior PB and Inferior MI.


P-lwave
Normal values

upin

all leads except aVR.

<

2.5 mm.

< 2.5 mm.

Abnormalities
Junctional rhythm.
LAE

RAE

Atrial flutter

Atrial ?brillation


Pwave abnormality


PR interval
The time
intewal between
beginning of P—wave to WPW syndrome
beginning of QRS
complex. .
3_ Flrst degree heart
block
5mm (0.12—0.2 sec