1. ECG update
FOR PARAMEDICS & JUNIOR MEDICAL
OFFICERS
DR LEE OI WAH

2. A POEM BY MOTHER TERESA :
“ life is an opportunity benefit from it,
Life is a dream, realize it,
Life is a challenge, meet it,
Life is a struggle, accept it,
Life is too precious, do not give up on it,
Life is life, fight for it.”

3. Heart, front view

4. The intrinsic conduction system of the heart and
succession of the action potential through selected
areas of the heart during one heart beat.

5. The Standard 12 Lead ECG
The standard 12-lead electrocardiogram is a
representation of the heart's electrical activity
recorded from electrodes on the body surface.

6. Frontal and Horizontal Plane Lead Diagram

7. RV + Septal + LV
= AC. ANTERIOR

8. FACTORS AFFECTING THE ECG
1. ECG recorded with patient lying comfortable, relaxed in
bed. Explain procedure to apprehensive patient to ally
anxiety and reduce muscle twitching.
8
2. Good contact between skin and electrode.
3. ECG machine properly standardized - 1 mV to produce
1 cm deflection.
4. Patient and ECG machine must be properly grounded to
avoid alternating current interference.
5. Any electronic equipment with patient can produce
artifacts.

9. Schematic representation of normal ECG trace (sinus
rhythm), with waves, segments, and intervals labeled.

10. 1. Measurement
2. Rhythm
3. Conduction
4. Waveform description

12. MEASUREMENT

13. CALCULATION OF THE HEART RATE
Time: Each small square = 0.04 seconds
Each large square = 0.2 seconds (5 small
squares)
QRS rhythm: When normal is usually regular.

14. HEART RATE
CALCULATION OF THE HEART RATE
Heart Rate: number of QRS complexes in 6 secs x 10

18. ECG NOMENCLATURE
P WAVES
Represent sequential activation (depolarisation) of the
Right & Left atrial and therefore originate from the
SAN, and it is common to see notched or biphasic P
waves of right and left atrial activation.
 Usually precede the QRS complex
• P duration < 0.12 sec
• P amplitude < 2.5 mm

19. ECG NOMENCLATURE
P WAVES
 May be:
 Bifid and broad (notch & M-shaped) (>3 small
squares wide in left atrial hypertrophy in leads I, II
& aVL
 Peaked (>3 small squares tall) in right atrial
hypertrophy in leads II, III, aVF
 Lost of inverted in ectopic rhythm and tachycardias
 Lost in or dissociated from the QRS complex

20. ECG NOMENCLATURE
Normal P waves Inverted P waves
Absent P waves Two P waves to each QRS

21. ECG NOMENCLATURE
PR interval
 Represent the time take for excitation to spread from
the SA node down over the atria to the AV node, down
thro' the bundle of His, and to the ventricular muscle.
 Measured from beginning of P wave to beginning of
QRS complex. Represent total time required for impulse
for depolarisation of atria (P wave) as well as time
required for impulse to travel slowly through the AV
junction, through the bundle branches, just up to the
point of ventricular depolarisation (QRS complex).

22. ECG NOMENCLATURE
PR interval
 Normal: 0.12 secs - 0.20 secs
(3 small squares to <5 small squares).
 May be:
Short in:
 Infants, drugs (e.g steroids) 
Wolf Parkinson White syndrome and other pre-
excitation syndromes ( accessory pathway bypass
AV junction)

23. ECG NOMENCLATURE
PR interval
Prolonged in:
 # Drug effect (digitalis, beta blockers, Calcium Channel
 Blockers.
 # Hyper trophy, Atrial Dilatation, Degenaration (aging),
 Myocardial Infarction (Inf. MI)
 # First Degree Heart Block
 # Second Degree Heart Block
 # Third Degree Heart Block

24. PR interval

25. PR interval
a) 2nd Degree Type 1
b)

26. PR interval
Prolonged PR: > 0.20s
AV dissociation / 3rd degree HB:
Some PR's may appear prolonged, but the P waves and QRS
complexes are dissociated (i.e., not married, but strangers
passing in the night).

27. J-point
QRS complexes (interval)
 Represents the time taken for excitation (depolarisation)
to spread through both the ventricles (simultaneously)
 Measure from beginning of QRS complex to its end
point, called the J-point.
 In normal sinus rhythm should be:
 Preceded by a P wave
 <0.12 seconds (< 3 small squares)

28. QRS complexes (interval)
 Will be:
 Wide (3 or more small squares) in
 bundle branch block
 in ventricular ectopics beats (VPCs)
 ventricular rhythms.
 If early or abnormal, may be caused by:
 An ectopic ventricular focus causing premature
ventricular contractions (PVCs).
 A ventricular tachycardia:
 Broad complex: 0.12 seconds or more
 Usually arise from a single ectopic focus

29. QT INTERVAL
 Represents total time required for both
depolarisation and repolarisation of the ventricles
to occur. Measured from the beginning of QRS
complex to the end of T wave.
 Normal QT interval : 0.35 to 0.45 second.
 Length of QTI normally varies according to age,
gender& especially heart rate .
 Electrolyte abnormalities (K+, Ca++, Mg++) & certain
antidysrhythmic drugs, tricyclics, phenothiazines can
prolong QTI.

30. QT INTERVAL
 CNS disease (especially subarrachnoid hemorrhage,
stroke, trauma)
 Coronary Heart Disease (some post-MI patients).
 Indicates a state of increased vulnerability to
malignant ventricular arrhythmias, syncope, and
sudden death.
 The prototype arrhythmia of the Long QT Interval
Syndromes (LQTS) is Torsade-de-pointes, a
polymorphic ventricular tachycardia characterized
by varying QRS morphology and amplitude around
the isoelectric baseline.

31. ST segment
 Represents the interval of time between the
end of the QRS complex (a juncture called the J-
point) and the beginning of the T wave.
 Though not a true wave form, the ST segment
represents the interval during which the
myocardium remains at rest in a depolarised state
and the beginning of ventricular repolarisation.
 Shape and position relative to baseline should be
isoelectric and may be altered with episodes of
ischemia, metabolic abnormalities, drug effects and
other conditions.

32. ST segment
 There may be:
 Convex elevation in myocardial infarction
 Concave elevation in pericarditis
 Depression: Ischemia, digoxin toxicity, and
left ventricular hypertrophy.
 In AMI, the ST segment elevation (or reciprocal
depression) occurs in the leads representing the
site of the infarction (12 lead ECG):
 Anterior : Leads V2 - V5 (often in I and AVL)
 Inferior : Leads II, II, AVF
 Septal : Leads V1 - V4
 Lateral : Leads I, AVL, V4 -V6

33. ST segment

34. ST segment
ST segment depression is often characterized
as "upsloping", "horizontal", or "downsloping".

35. T wave
 Represent end of ventricular repolarisation of ventricles.
 Should be in the same direction as the QRS complex.
 Slightly rounded and asymmetrical and usually exhibit a
smooth takeoff from the end of the ST segments.
 If inverted, may be a sign of myocardial ischemia,
infarction, ventricular hypertrophy or metabolic abnormalities,
but are often non specific.

36. ECG INTERPRETATION
What is the rate ? …………………………………
What is the rhythm ? …………………………………
Is there a “P” wave ? ………………………………..
Describe the “P” wave …………………………………
Is there QRS complex …………………………………
Describe the QRS complex ………………………………..
What is the PR interval? ………………………………….
Is there a “T” wave? …………………………………..
Describe the “T” wave ……………………………………
Describe the ST segment …………………………………..
What is the name of the RHYTHM ………………………………