Lecture By Dr.Haifa Khedier ER Doctor. MGH Madinah, KSA

1. What Makes ECG
MYOCYTES PRODUCE
Electrical impulse
Human body
conducting impulse
Electrodes pick up
potential difference
ECG Machine read
potential difference
, and draw a graph

2. What is electrode ?
 Special Sensor devices
 Connected to certain
areas in the body
 Pick up potential
difference
 They known as leads

3. Types of leads ( Electrodes )
Bipolar
Limb Leads
Unipolar
Leads
Chest leads
V1 to V6

4. What is Bipolar leads
Lead 1
Lead 11
Lead 111
• +ve LA
• -ve RA
• +ve LL
• -ve RA
• +ve LL
• -ve LA

5. Bipolar Limb Leads
Can be located at any
part of the limb 10 cm
from the heart
They form equilateral
triangle Einthoven
triangle

6. Augmented Unipolar leads
aVR
• +ve
• RA
aVF
• +ve
• Lf
aVL
• +ve
• LA

7. Augmented Unipolar leads
• No Negative pole
• Instate the reference is
the other two leads
• The machine change
the leads without
addition of attached
devices

8. Chest leads Location
V1 Rt
4th IC
V2 Lt
4th IC
V3
HALF
WAY
V2&V4
V4 LT
5th IC
V5 5th
IC , AAL
V5 5th
IC ,MAL

9. Hexaxial system
• Two victors(leads) are equal
in intensity ,and polarity as
long as they are parallel
• Accordingly we can shit the
leads to a point passing
through the heart
center, and they will be the
same
• The location of the lead is
determined by its positive
pole
• Direction of the Lead is
from Positive to Negative
electrode

10. • The direction of the
unipolar lead is towards
the center of the
corresponding limb of
the triangle, otherwise
same is applied as in
bipolar leads

11. Hexaxial system

12. Anatomical representations of the
leads

13. Anatomical representations of the
leads

14. ECG paper

15. ECG paper

16. ECG paper
Calibration Box
 Found at edge of ECG
paper
 Standard 10 mm
height (1MV )
 .2 second width
 To confirm standard
ECG format


17. ECG Components
Waves
Segment
Interval
• A deflections from the base line represent
cardiac event
• P- QRS- T waves
• A specific portion of the complex
• PR – ST
• Distance measured as time between two
cardiac events
• QT- PR- TP

18. Waves
Waves represent :
 Atrial , or ventricular
depolarization , repolarization
and conduction
 Can be positive ,negative or
biphasic deflection from the
baseline
 Baseline from one TP
segment to the next

19. ECG Representation of cardiac events
•
•
•
•
•
•
Atrial depolarizatio
Atrial Repolarization
Conduction
Ventricular depolarization
Ventricular Repolarization
Conduction

20. ECG Segments & Intervals
Segments
Intervals
Additional
intervals
PR
PR
RR
ST
QT
PP

21. P- Wave
• First wave after TP
• Represent atrial depolarization
and conduction
• Duration 0.08 – 0.11 second
• Direction of the impulse is
downwards & to the left
• It is upright in leads 11,111,& aVf
• Downwards in aVR
• It must be upright in Leads 11 &
aVF to say sinus rhythm

22. TP wave
• Represent
repolarization of Atria
• Usually not seen
• It occurs when there is
no QRS after P as in Av
dissociation
• It can also be seen in PR
or ST depression

23. PR Segment
• From end of P to
beginning of QRS
• Usually at the base line
• Depression of up to
0.8 mm is accepted as
normal
• Pathological depression
in pericarditis and atrial
ischemia

24. PR Interval
• Include P wave ,and PR
segment
• Cover the event from
initiation of impulse at SA
node to start of
ventricular depolariz.
• Duration o.12 sec. to 0.20
sec.
• < 0.11 shortening
• > 0.20 1st degree heart
block

25. QRS Complex
• Composed of two or
more waces
• Represent ventricular
depolarization
• Duration is up to 0.12
second

26. How to identify different waves
Q
wave
R
wave
S
wave
• The first negative wave
after P wave
• The first Positive wave
after P wave
• The first negative
deflection after R wave

27. An X Prime wave
•
•
•
•
•
Extra wave in QRS
It isn't an actual wave
Change in QRS
QRS become bizarre
S wave : only when
cross the baseline

28. Q Wave
Can be significant if :
 0.03 second or wider
 Equal to or greater than
1/3rd of height of R
wave
Non significant Q wave
 Commonly found in
Leads : 1 , aVL & V6

29. The Intrinsicoid Deflection
• Beginning of QRS to the
beginning of negative down
slope of the R wave when no Q
wave
• Represent the time of electrical
impulse from purkinje fibers to
surface of epicardium
• It is longer in left preicordial
leads V5, V6
• Prolongation in LVH , BBB

30. The ST Segment
• End of QRS to Beginning of T
• Usually along the base line
with normal variation of 1
mm in limbs leads & 3 mm in
Right chest leads
• The point of junction with
QRS is called J point
• Represent the period from
depol. to repol. of ventricles

31. The T Wave
• Represent ventricular
repolarization
• negative or positive
deflection after ST
Segment
• Should be The same
direction of QRS
• It is asymmetric , begin
sloping and end is faster

32. How to measure asymmetry
• Draw a line from the
peak of T wave to the
base line , and measure
each side
• Asymmetry is usually a
sign of pathology , but
may be normal

33. QT Interval
 QRS + ST + T
 Represent all the event of
ventricular systole
Varies with Rate ,age sex
, and electrolyte
abnormality
prolongation predispose
to arrhythmias

34. Best way to measure QT Interval
• Normal QT Is less than the half of R-R Interval
• Accordingly lengthen when the heart rate
slow, and shorten when fast
• This makes it hard to calculate the interval at
which QT is normal

35. QTc Interval
•
•
•
•
•
Stand for QT corrected Interval
Corrected for the heart rate
QTc interval calculation is the best way.
Normal QTc :
0.410 second
prolonged QTc : > 0.419 second

36. QTc Interval Equation
QT
1.75(VR-60)
QTc

37. U - Wave
• A small flat wave sometimes
seen after the T wave
• Representation unknown
• Clinical significance :
Hypokalemia
Hyperkalemia
Inaccuracy in measuring
QT segment

38. Additional Intervals
• R-R Interval
• The distance between
peaks of R waves in two
consecutive QRS
• P-P interval
• Distance between two
identical points of one P
to the next
• These intervals are useful
in evaluation of Rhythm