The document provides an overview of basic electrocardiography (ECG) principles, explaining the electrical activity of the heart and how it is recorded using electrodes. It outlines the interpretation of ECG waveforms, segments, and intervals while detailing the positioning of leads used for recording and standardization methods. The text includes information on how to analyze heart rate, rhythm, and the cardiac electrical axis, along with specific criteria for abnormal axis deviations.

1. Basic
Electrocardiography
By
Dr. Ahmed Easa

2. What is ECG
►It is recording of electrical activity of the
heart.

5. Basic concepts
► The normal resting excitable
cardiac cells have differential
charge distribution with their
outside being positive in
relation to their inside at
rest (Polarized state).

6. ► With activation the charge distribution reverses
and this reversal propagates through the cardiac
cells producing a propagated action potential(
Depolarized state).
Basic concepts

7. ►The junction between the depolarized and
polarized portion on the surface of cardiac
myocyte form an electric dipole.
Basic concepts

8. ►The voltage produced by cardiac dipole can
be recorded by applying electrode over the
surface of the heart.
Basic concepts

9. Currents and Voltages
► At rest, Vm is
constant
► No current flowing
► Inside of cell is at
constant potential
► Outside of cell is at
constant potential
++++++++++++++++++
------------------------------
A piece of cardiac muscle
outside
inside
0 mV
+-

10. Currents and Voltages
► During AP upstroke,
Vm is NOT constant
► Current IS flowing
► Inside of cell is NOT
at constant potential
► Outside of cell is
NOT at constant
potential
++++------------------------
------++++++++++++++
A piece of cardiac muscle
outside
inside
Some positive
potential
+-
current
AP
An action potential propagating
toward the positive ECG lead
produces a positive signal

11. More Currents and Voltages
A piece of cardiac muscle
outside
current
+-
No voltage
+-
A negative voltage reading
------++++++++++++++
inside
++++------------------------

12. More Currents and Voltages
current
-------------------------------
A piece of totally depolarized
cardiac muscle
outside
inside
+++++++++++++++++++
Vm not changing
No current
No ECG signal
+++++++-------------------
A piece of cardiac muscle
outside
inside
------------+++++++++++
During Repolarization
+-
Some negative potential
Repolarization spreading toward
the positive ECG lead produces
a negative response

13. ►If the wave of depolarization spreads towards
the electrode --- positive deflection is recorded.
►If the wave of depolarization spreads away
from the electrode --- negative deflection is
recorded.
►If the wave of depolarization spreads
orthogonal to the electrode --- biphasic
deflection is recorded.

14. ►If the wave of repolarization spreads towards
the electrode --- negative deflection is
recorded.
►If the wave of repolarization spreads away from
the electrode --- positive deflection is recorded.
►If the wave of repolarization spreads
orthogonal to the electrode --- biphasic
deflection is recorded.

15. Dipole voltage
2
cos( )
dipole
M
V
r


------++++++++++++++
inside
++++------------------------
Observation
point

16. ►The cardiac dipoles activating the
individual cardiac myocyte add vectorially
and are represented by a single vector.

17. ►The direction of this vector changes
continuously with time giving rise to
instantaneous vector .

18. Surface Electrocardiographic leads
*12 standard leads
► More leads can be added for special purposes
► The are subdivided into
 Limb leads
 Chest leads

19. Surface Electrocardiographic leads
► They are of 2 types
 Bipolar record voltage or potential difference between
2 sites in the heart as standard limb leads I,II,III)
 Unipolar leads directly record the voltage at the site
of application ( Augmented limb leads and chest
leads)
► Standardization:-
►Paper speed 25 mm/sec always look for ( rapid speed 50
mm/sec may lead to false diagnosis of bradycardia).
►10 mm = 1 milivolt

20. Limb Leads
► Limb leads
 Record electrical activity in
the frontal plane
 Two types
►Nonaugmented Lead I,II,III.
►Augmented aVR, aVL, aVF

21. Chest Leads
► Position of chest leads:-
 V1 right fourth intercostal space at sternal edge
 V2 left fourth intercostal space at sternal edge
 V3 midway between V2 & V4
 V4 left fifth intercostal space in midclavicular line
 V5 in anterior axillary line on the same horizontal level
of V4
 V6 in mid axillary line on the same horizontal level of V4
► They record the electrical activity in the horizontal
plane

22. V1 V2
V4 V5 V6
V3

23. Anatomical relations of the leads
►Anterior wall of LV ---V1-V4
►Lateral wall of LV ----- 1,aVL,V5 & V6
►Inferior wall of LV----- 2,3,aVF
►RA & LV cavity ----- aVR & V1
►RV ---- V3R & V4R

24. How to comment on ECG
►1-Rate
►2-Rhythm
►3-Cardiac axis.
►4- Analysis of individual waves, segments
and intervals.
►5- ECG findings specific to disease states.

25. 1- RATE
► Normally 60-100 Bpm
► Less than 60 ---- Bradycardia
► More than 100 --- tachycardia
► How to calculate heart rate from ECG
► 1-Regular:-
► Measure the number of small squares between 2 successive R waves
and divide 1500 upon it.
► Measure the number of large squares between 2 successive R waves
and divide 300 upon it.
► One small square = 40 msec
► One large square = 200 msec
► 2-Irregular
► Count the number of R waves in 10 seconds and multiply by 6.

27. 2-Rhythm
►The normal cardiac rhythm is regular
►Irregular rhythm may be present in
 Atrial fibrillation
 MAT
 Atrial flutter with varying conduction
 PVCs, PACs
 Mobitz type 1 second degree AV block

28. 3-Cardiac electrical axis
►The electric axis is a fundamental and general
term
►It can be applied to any wave or segment e.,g(
P, QRS,T,U,ST segments)
►Due to 3 dimensional cardiac geometry, the
axis can be calculated in the 3 orthogonal
planes (Frontal, Sagittal & Horizontal)

29. ►The simplest & commonest form of axis
calculation is the mean frontal plane QRS.
 Normal mean frontal QRS axis (-30 ---- +110)
 Left axis deviation< -30
 Right axis deviation > 110
3-Cardiac electrical axis

30. How to calculate the QRS axis
►1-The easiest way
► Hold the SINGLE lead ECG strip with your hands
► Put your right hand over lead III
► Put your left hand over lead I
► Look for QRS in lead 1& lead 3
 Positive in lead 1 negative in lead 3 ---LAD
 Positive in lead 3 negative in lead 1 ---RAD
 If both negative ( extreme axis deviation) NO MAN
LAND
 If both positive the axis is within normal

31. ►2- More difficult way
►Choose a lead with a biphasic QRS.
►The axis lie perpendicular to this lead.
►Look for the perpendicular leads or the leads
close to the perpendicular leads.
►Normally there is only 2 perpendicular leads for
any lead you choose.
►The lead that shows positive QRS, the axis is in
that direction

32. 3-Exact calculation of mean frontal
QRS axis
► 1- Pick up 2 orthogonal leads (
Lead 1 & aVF)
► 2- For lead 1 calculate the net
QRS voltage ( - for negative
waves Q&S, + sign for positive
waves R)
► 3- For lead aVF do the same
and multiply the resultant by
2/3
► 4-Divide net QRS voltage in aVF
over net QRS voltage in lead 1.
► 5- The angle the mean frontal
QRS vector make with the
horizontal axis is given by
2
arctan
3
aVF
I
QRS
QRS

 
  
 

34. I
avF+60III+120
avL-30avR-150
-90
+90
+/-180 0
LAD
RAD
Extreme axis deviation
No man”s land

+
+
-
-

35. Abnormal QRS axis
► Left Axis Deviation (LAD): > -30o (i.e., lead II is mostly 'negative')
 Left Anterior Fascicular Block (LAFB): rS complex in leads II, III, aVF, small q in
leads I and/or aVL, and axis -45o to -90o
 Some cases of inferior MI with Qr complex in lead II (making lead II 'negative')
 Inferior MI + LAFB in same patient (QS or qrS complex in lead II)
 Some cases of LVH ( hypertrophy mainly involves the posterobasal part of LV)
 Some cases of LBBB
 Ostium primum ASD and other endocardial cushion defects
 Some cases of WPW syndrome (large negative delta wave in lead II)

36. ► Right Axis Deviation (RAD): > +90o (i.e., lead I is mostly 'negative')
 Left Posterior Fascicular Block (LPFB): rS complex in lead I, qR in leads II, III,
aVF (however, must first exclude, on clinical basis, causes of right heart
overload; these will also give same ECG picture of LPFB)
 Many causes of right heart overload and pulmonary hypertension
 High lateral wall MI with Qr or QS complex in leads I and aVL
 Some cases of RBBB
 Some cases of WPW syndrome
 Children, teenagers, and some young adults
 Bizarre QRS axis: +150o to -90o (i.e., lead I and lead II are both negative)
(No man land)
► Consider limb lead error (usually right and left arm reversal)
► Dextrocardia
► Some cases of complex congenital heart disease (e.g., transposition)
► Some cases of ventricular tachycardia

37. 4-Waves, intervals and segments

39. P wave
► Represents atrial depolarization
► Criteria of normal P wave
 Upright in lead II & avF
 Negative in lead avR
 Variable in lead aVL
 Biphasic in V1 with initial positive deflection and late
negative deflection
 Not more than 0.25 mv in amplitude
 Not more than 120 msec in duration
 2.5 x 2.5 small squares
 If notched look for the distance between 2 notches –
normally less than or equal to one small square

40. P-R interval
► Represents time taken by the impulse to travel via
the AV node, His bundle, Bundle branches and
Purkinje fibers.
► Measured from beginning of P wave to the
beginning of QRS complex
► Normally 120-220 msec ( 3-5.5 small squares)
► Prolonged in AV block (see later)
► Shortened in preexcitation syndromes (see later)

41. QRS
►Q wave:- Any initial negative deflection
►R wave any initial positive deflection
►S wave negative wave following the R wave.
►Small letters are used if the amplitude of
the wave is less than 5 mv and capital
letters are used if the amplitude is more
than 5 mm.

42. QRS
►Sequence of ventricular activation
 1- Septal depolarization
►Initial vector directed across the interventricular
septum from left to right
►Produces small r wave in V1 and small q in V5,V6
 2-Ventricular free wall depolarization
►Simultaneous depolarization of LV & RV.
►Because normally the LV is thicker than the RV its
electrical forces predominate
►This lead to large S wave in V1 & large R wave in
lead V6

43. QRS
►Transitional Zone
 Zone at which there is change from
predominantly negative QRS to predominantly
positive QRS
 Usually between V3-V4
 Delayed transitional zone– shifted to V5&V6---
clockwise rotation in RV enlargement
 Early transitional zone– shifted to V1&V2---
counterclockwise rotation in LV enlargement

44. J point
►Junction between the end of QRS and
beginning of ST segment
►J point loss may be the first ECG sign of
acute MI.

45. ST segment
►From the end of QRS complex to the
beginning of T wave
►Represent phase 2 of myocyte action
potential
►Normally it is iso electric with the
preceeding TP segment

46. T wave
► Represent phase 3 of myocyte action potential.
► Due to asynchronous repolarization of subendocardial
and subepicardial myocardium ( Normally
subepicardial repolarization precedes subendocardial
repolarization)
► Usually positive in precordial leads
► May be negative in V1 & V2
► Isolated T inversion in V2 is pathologic.
► Persistent juvenile pattern is T wave inversion in RT
precordial leads especially in blacks
► Asymmetric T wave inversion is pathologic.
► Symmetric T wave inversion is non specific

47. QT interval
►The interval from beginning of QRS to the
end of T wave.
►Represents the total time of ventricular
electromechanical systole
►Normally up to 440 msec ( or roughly less
than half the corresponding RR interval)

48. U wave
►A small positive wave may occasionally
follow the T wave
►May represent repolarization of the
posterobasal portion of the LV.

49. Thank You