Review of the anatomy and physiology Review of the conduction system ECG:basics term, ECG RECORDING: leads, electrodes, waveforms and intervals Determining heart rate ECG Analysis/Interpretation -Normal ECG & Abnormal ECG

1. ECG/EKG

2. Outline
1. Review of the anatomy and physiology
2. Review of the conduction system
3. ECG:basics term,
4. ECG RECORDING: leads, electrodes,
waveforms and intervals
5. Determining heart rate
6. ECG Analysis/Interpretation
-Normal ECG & Abnormal ECG

3. The Heart
• The heart consists of four
chambers
– The right atrium and right
ventricle: responsible for
delivery of deoxygenated
blood to lungs
– The left atrium and left
ventricle: responsible for
delivery of oxygenated
blood to the body

4. The Normal Conduction System

5. ECG-TERMS
Electrocardiography
-A graphical representation of the electrical
events of the cardiac cycle.
Electrocardiogram
-A record of electrical activity of the heart.
Electrocardiograph
-A device used to record electrical activity of the
heart.

6. What types of pathology can be identified from
ECGs?
• Arrhythmias
• Myocardial ischemia and infarction
• Pericarditis
• Chamber hypertrophy
• Electrolyte disturbances (i.e. hyperkalemia, hypokalemia)
• Drug toxicity (i.e. digoxin and drugs which prolong the
QT interval)

7. RECORDING OF ECG
ELECTRODE PLACEMENT
Electrodes
- are adhesive pads that contain a conductive gel
and are attached to the pt’s skin.
- skin sensors by which the ECG records electrical
activity of the heart
note: ensure good skin contacts and adequate
conductive jelly in the center

8. LEADS
Paired electrodes
• A record of electrical activity between two
electrodes
• 3 types of leads: standard limb leads, augmented
leads and precordial leads
• Each lead has a positive (+) and negative(−)
charge

9. EKG Leads
Leads are electrodes which measure the
difference in electrical potential between either:
1. Two different points on the body (bipolar leads)
2. One point on the body and a virtual reference point
with zero electrical potential, located in the center of
the heart (unipolar leads)

10. EKG Leads
The standard EKG has 12 leads: 3 Standard Limb Leads
3 Augmented Limb Leads
6 Precordial Leads
The axis of a particular lead represents the viewpoint
from which it looks at the heart.

11. Standard Limb Leads

12. Standard Limb Leads

13. Augmented Limb Leads

14. All Limb Leads

15. Precordial Leads
Adapted from: www.numed.co.uk/electrodepl.html

16. Precordial Leads

17. Summary of Leads
Limb Leads Precordial Leads
Bipolar I, II, III
(standard limb leads)
-
Unipolar aVR, aVL, aVF
(augmented limb leads)
V1-V6

18. Arrangement of Leads on the EKG

19. Anatomic Groups
(Septum)

20. Anatomic Groups
(Anterior Wall)

21. Anatomic Groups
(Lateral Wall)

22. Anatomic Groups
(Inferior Wall)

23. Anatomic Groups
(Summary)

24. WAVEFORM
ECG-recording of electrical impulse produced bythe heart
• The body acts as a giant conductor of electrical currents.
• Any two points on the body may be connected by electrical
leads to register an ECG or to monitor the rhythm of the
heart
• Tracing recorded from the electrical activity of the heart
forms a series of waves & complexes that have been
arbitrarily labeled the P,Q,R,S and T waves
• These waves or deflections occur in regularly occurring
intervals in the healthy individual.

25. Waveforms and Intervals

26. Normal ECG Signal
• P – atrial
depolarization
• QRS complex –
ventricular
depolarization
• T – ventricular
repolarization

27. P wave
• Represents atrial depolarization
• Look like a small upward hill or bump
• Precedes QRS complex
• Amplitude/height not more than 2-3mm
• Duration/width should be less than 0.12s or 3 small
squares
• Waveform upright and symmetrically rounded in leads
I,II,AVF and v4-v6

28. Cont……
• Inverted in aVR
• Diphasic ,flat or inverted in leads III,V1 and V2
• If peaked or notched indicates abnormal depolarization
of one or both atria due to chamber enlargement or
conduction defects

29. QRS Complex
• Comprise 3 waves; Q, R and S
• Represents ventricular depolarization
• Components of QRS complex vary depending
upon which ECG lead is used for recording
• QRS amplitude is much higher than the height
of the P wave .

30. Q wave
-First –ve or downward deflection after P wave
- May or may not be present
- Preceding R wave
- Reflects normal ventricular activity

31. R wave
• First positive deflection after P wave
S Wave
-Negative deflection after R wave
Note
-Duration/width should be less than 0.12
-Prolonged QRS complex indicates delayed
conduction in one or more of the bundle
branches

32. T Wave
• Represents ventricular recovery after
depolarization
• Positively deflected in leads I,II & V3-V6
• Inverted in lead avR
• Variable deflection in leads III, avL, V1 and V2
• Amplidude /height should not exceeds 5mm in
limb leads or more than 10mm in precordial leads

33. T wave cont…
• May be diminished, elevated or inverted due to
drugs, electrolyte imbalance, injury & ischemia
• Last half to one third of T wave referred to as
vulnerable period
Why? -an electrical stimulus during this portion of
T wave may precipitate a serious dysrhythm

34. U Wave
• A small and usually positive deflection
• Immediately following the T wave
• Low amplitude
• Small and usually unidentifiable
• Significance unknown
• Thought to result from slow repolarization of intra
ventricular conduction system
• Visualized best in Lead v3

35. Segments and Intervals
Intervals
1.PR Intervals
-short period of electrical inactivity
-From begining of P wave to onset of QRS
complex
-Duration normally 0.12-0.20 secs
-Greater than 0.20 indicates conduction
delay/depression through A-V node

36. Cont…..
secondary to drugs e.g digitalis, ANS supply
defects
-Shortened PR Interval indicates impulse
bypasses A-V node leading to early ventricular
stimulation .

37. QT Interval
• From beginning of QRS complex to end of
T wave
• Reflects time period/interval of ventricular
depolarization and repolarization
• Parameter varies according to: Heart rate and
gender
• Increased hr produces shortened QT
• Decreased hr produces prolonged QT interval

38. Prolonged QT interval due to
-Myocarditis
-IHD
-Rheumatic fever
-Cerebro-vascular disease
-Electrolyte imbalances esp hypocalcaemia
-Drug therapy
-Disopyramide
-Amiodarone

39. Cont…..
-Hypothermia
Shortened QT interval
-Digitalis
-Hypocalcaemia
-Potassium intoxication

40. ST Segment
• Isoelectric line following QRS complex
• Time interval during which ventricles have completely
depolarized and are beginning repolarization
• From junction btn end of QRS complex and beginning
of ST segment (J point) to beginning of T Wave
• Isoelectric that is at baseline
• May be elevated up to 1 mm in limb leads or 2mm in
precordial leads
• Normally not depressed more than 0.5mm

41. NORMAL ECG: Record Paper
• Recorded on graph paper
• Each small box equal to 1mm square
• 5th small box marked by a darker line
• Darker lines form large square incorporating
• 25 smaller squares

42. ECG: Measurement/Parameter
• Vertical measurement
-amplitude or voltage in millivolts or millimeters
-indicates magnitude or strength of force
-1 small box=0.1mV or 1mm
-1 large square=0.5mV or 5mm
• Horizontal measurement
- duration or time in seconds
5 large square = 1 seconds
1 large square =0.20sec
1 small square=0.04

43. Standardization
• Vertical Measurement
- 0.5mV=5mm × 2=2 boxes vertically(10mm)
- If deflection too large: half
- If deflection too small: double
• Horizontally/Duration(standard paper speed)
-25 seconds out of (10,25,50)
- If too fast double
- If too slow half

44. Analysis of ECG: Steps
• Rate
• Rhythm
• Axis
• P wave
• PR Interval
• QRS Complex
-Q wave
-R wave

45. Cont……
R wave-right and left ventricular hypertrophies
- bundle branch blocks
• ST segment
• QT Interval
• T wave
• U wave

46. Rate
-Calculate atrial and ventricular rate
Normal findings
-HR –btn 60-100 beats/minute
-Atrial rate the same as ventricular rate
Abnormal findings
-Hr>100b/m-tachycardia
-Hr<60 b/m- bradycardia

47. How to calculate
1. Six second method
-print a six second strip
-add up the number of R waves and
multiply by 10
e.g. If there are 8 R waves in 6 seconds strip
Rate =8 × 10 which is 80b/m

48. Large box method
VR=300/no of large square btn 2 R wave
AR=300/no of large square btn 2 P wave
Small Box Method
VR=1500/no of small squares btn R waves
AR=1500/no of small squares btn P waves

49. Rhythm
• Is it regular or irregular?
How to do?
- March R-R interval in different lead
- Look for similarities
- If similar-regular rhythm
- If varies-irregular

50. Cont….
Normal findings
-R-R intervals are regular
-P-P intervals are regular
-There is one P for every QRS
Abnormal Findings
- R-R intervals are irregular
- -P-P intervals are irregular
- There is more than one P for each QRS

51. P Wave
-Presence (hunt for P)
-Regular interval
-Shape-symmetrical ,upright and round
-Uniform (look alike) and point same direction
-P:QRS ratio should be 1:1
Abnormal
-P wave not followed by a QRS complex
-There are more P waves than QRS

52. The QRS Axis
The QRS axis represents the net overall direction
of the heart’s electrical activity.
Abnormalities of axis can hint at:
Ventricular enlargement
Conduction blocks (i.e. hemiblocks)

53. The QRS Axis
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 (RAD)

54. Determining the Axis
• The Quadrant Approach
• The Equiphasic Approach

55. Determining the Axis
Predominantly
Positive
Predominantly
Negative
Equiphasic

56. The Quadrant Approach
1. Examine the QRS complex in leads I and aVF to
determine if they are predominantly positive or
predominantly negative.
• The combination should place the axis into one of the
4 quadrants below.

57. The Quadrant Approach
2. In the event that LAD is present, examine lead II to
determine if this deviation is pathologic.
• If the QRS in II is predominantly positive, the LAD is
non-pathologic (in other words, the axis is normal).
• If it is predominantly negative, it is pathologic.

58. Quadrant Approach: Example 1
Negative in I, positive in aVF  RAD
The Alan E. Lindsay
ECG Learning Center
http://medstat.med.utah.
edu/kw/ecg/

59. Quadrant Approach: Example 2
Positive in I, negative in aVF  Predominantly positive in II 
Normal Axis (non-pathologic LAD)
The Alan E. Lindsay
ECG Learning Center
http://medstat.med.utah.
edu/kw/ecg/

60. All Limb Leads

61. The Equiphasic Approach
1. Determine which lead contains the most
equiphasic QRS complex. The fact that the QRS
complex in this lead is equally positive and
negative indicates that the net electrical vector (i.e.
overall QRS axis) is perpendicular to the axis of
this particular lead.
2. Examine the QRS complex in whichever lead lies
90° away from the lead identified in step 1. If the
QRS complex in this second lead is predominantly
positive, than the axis of this lead is approximately
the same as the net QRS axis. If the QRS complex
is predominantly negative, than the net QRS axis
lies 180° from the axis of this lead.

62. Equiphasic Approach:
Example 1
Equiphasic in aVF  Predominantly positive in I 
QRS axis ≈ 0°
The Alan E. Lindsay ECG Learning Center ; http://medstat.med.utah.edu/kw/ecg/

63. Equiphasic Approach:
Example 2
Equiphasic in II  Predominantly negative in aVL 
QRS axis ≈ +150°
The Alan E. Lindsay ECG Learning Center ; http://medstat.med.utah.edu/kw/ecg/

64. P - R Interval
• Time travel from SA to AV nodes
• Is btn 0.12 - 0.20 sec
• Constant intervals throughout rhythm
Abnormal findings
-PR interval is > 0.20s-delayed travel time from
SA to AV node
-Interval irregular-SA to AV conduction
problem and possible conduction heart block

65. QRS Complex
-Duration not more than 0.12sec
-Uniform(same size, shape and direction)
-R-R interval btn each QRS is regular.
Abnormal Findings
• Vary in shap, width and direction
• QRS complex is >.12s wide
• R to R interval btn each QRS is irregular

66. ST wave
• ST segment be sitting on isoelectric baseline
• No > 1mm above or below isoelectric line
T wave
• Upright whenever R wave is upright
• Deflects downward when R wave is downward
Abnormal findings
• T wave is in the opposite direction than the R wave

67. What remains
• More on Q waves analysis
• More on R wave analysis
• Normal Sinus Rhythm
• Dysrythmias

68. PATHOLOGICAL Q WAVE
• Q wave > 0.04
• Q wave is 25% of R wave
R WAVE
•Notched-bundle block
•W or M shaped-bundle block
•R wave progression

69. HYPERTROPHY/ENLARGEMENT
• Right ventricular hypertrophy:
R ampl V1/V2 + S ampl V5/V6> 10.5 mm
• Left ventricular hypertrophy:
R ampl V5/V6 + S ampl V1/V2 > 30mm