- An ECG records the electrical activity of the heart over time using electrodes placed on the skin. It detects tiny electrical changes arising from the heart muscle contracting during each heartbeat. - The cardiac impulse originates in the sinoatrial node and travels through the atria and ventricles via specialized conduction pathways before the ventricles contract. - A standard 12-lead ECG provides multiple views of the heart to analyze the rate and rhythm of the heart as well as measure key intervals like the PR interval, QRS duration, and QT interval to identify any abnormalities.

1. NORMAL ECG
Prepared by: Dr Yousef Biuk

2. DEFINITION
• Electrocardiography (ECG) is the process of recording the
electrical activity of the heart over a period of time using
electrodes placed on a patient’s body. These electrodes
detect the tiny electrical changes on the skin that arise from
the heart muscle depolarizing during each heartbeat.

3. ACTION POTENTIAL

4. VENTRICULAR MUSCLE
CELL ACTION
POTENTIAL

5. ELECTROPHYSIOLOGY
• Cardiac impulse originates in the
Sinoatrial (SA) node
• Traverses the atria simultaneously –
no special conduction wires in atria
• Reaches AV node – delay
• Enters bundle of His and branches
through specialized conducting wires
called Purkinje network activates
both ventricles - QRS
• First the septum from L to R, then
right ventricle and then the left
ventricle and finally the apex
• Then the ventricles recover for next
impulse

6. PACEMAKER OF THE
HEART
• SA Node - Dominant
pacemaker with an intrinsic
rate of 60 - 100 beats/
minute.
• AV Node - Back-up
pacemaker with an intrinsic
rate of 40 - 60
beats/minute.
• Ventricular cells - Back-up
pacemaker with an intrinsic
rate of 20 - 45 bpm.

7. ELECTROPYSIOLOGY &
ECG

8. 12 LEAD ECG
• Standard ECG is recorded in 12
leads
• Six Limb leads – L1, L2, L3,
aVR, aVL, aVF
• Six Chest Leads – V1 V2 V3 V4
V5 and V6
• L1, L2 and L3 are called bipolar
leads
• L1 between LA and RA
• L2 between LF and RA
• L3 between LF and LA

9. ECG LEADS

10. CHEST LEADS

12. ECG PAPER
• X-Axis represents time - 1 mm = 0.04 sec
• Y-Axis represents voltage – 1 mm = 0.1 mV
• One big square on X-Axis = 0.2 sec (big box)
• Two big squares on Y-Axis = 1 milli volt (mV)
• Each small square is 0.04 sec (1 mm in size)
• Each big square on the ECG represents 5
small squares = 0.04 x 5 = 0.2 seconds
• 5 such big squares = 0.2 x 5 = 1sec = 25 mm
• One second is 25 mm or 5 big squares
• One minute is 5 x 60 = 300 big squares

14. ECG INTERPRETATION
• Rate: At usual speed (25mm/s) each ‘big square’ is 0.2s;
each ‘small square’ is 0.04s.
• To calculate the rate, divide 300 by the number of big
squares per R–R interval; or divide 1500 by the number of
small suares per R-R interval.

15. ECG INTERPRETATION
• Rhythm: If cycles are not clearly regular, use the ‘card
method’: lay a card along ECG, marking positions of 3
successive R waves. Slide the card to and fro to check that
all intervals are equal.

16. REGULA
R SINUS
RHYTHM
S

17. REGULAR
NON-SINUS
RHYTHMS

18. IRREGULA
R
RHYTHMS

19. ECG WAVES
• P Wave is Atrial contraction
– Normal 0.12 sec
• PR interval is from the beginning of P wave to the beginning
of QRS – Normal up to 0.2 sec
• QRS is Ventricular contraction – Normal 0.08 sec
• ST segment – Normal Isoelectic (electric silence)
• QT Interval – From the beginning of QRS to the end of T
wave – Normal – 0.40 sec
• RR Interval – One Cardiac cycle 0.80 sec

20. THE P-WAVE
• The normal P-wave:
• Has a smooth contour
• Is monophasic in lead II
• Is biphasic in lead V1
• upright in II, III, & aVF but inverted in aVR
• Has a duration 0f less than 0.12 sec or 3 small squares
• Height ˂ 2.5 small square

21. P-WAVE ABNORMALITIES
SEEN IN LEAD II
• In lead II two types of P-wave abnormalities can be seen.
• Right atrial enlargement is seen as a taller than normal P-
wave( increased amplitude) – P pulmonale
• Left atrial enlargement seen as a P-wave with a notch in it.
(Bifid P-wave) – P mitrale

22. OTHER P-WAVE
ABNORMALITIES
• Absent P wave: AF, sinoatrial block, junctional (AV nodal)
rhythm.
• Dissociation between P waves and QRS complexes
indicates complete heart block.

23. PR INTERVAL
• Measure from start of P wave to start of QRS
• Normal range: 0.12–0.2s (3–5 small squares)
• A prolonged PR interval implies delayed AV conduction (1st
degree heart block )
• A short PR interval implies unusually fast AV conduction
down an accessory pathway, eg WPW

24. HEART BLOCK
• 1st and 2nd degree (Mobitz I/II) heart block:
• 3rd degree AV (complete heart) block:

25. QRS COMPLEX
• normal duration: <0.12s. If ≥0.12s this suggests ventricular
conduction defects, eg: a bundle branch block
• Large QRS complexes suggest ventricular hypertrophy
• Normal Q wave <0.04s wide and <2mm deep (<25% R)
• Pathological Q waves may occur within a few hours of an
acute MI

26. BUNDLE BRANCH
BLOCK

27. LEFT VENTRICULAR
HYPERTROHPHY

28. RIGHT VENTRICULAR
HYPERTROPHY

29. ELECTRICAL AXIS
• The QRS electrical (vector) axis can have 4 directions
• Normal Axis - when it is downward and to the left –
southeast quadrant – from -30 to +90 degrees
• Right Axis – when it is downward and to the right –
southwest quadrant – from +90 to 180 degrees
• Left Axis – when it is upward and to the left – Northeast
quadrant –from -30 to -90 degrees
• Indeterminate Axis – when it is upward & to the right –
Northwest quadrant – from -90 to +180

32. CAUSES OF AXIS
DEVIATION
Causes of Left Axis Deviation:
• Left anterior hemiblock
• Inferior MI
• WPW syndrome
• LVH
Causes of Right Axis Deviation:
• RVH
• Pulmonary embolism
• Anterolateral MI
• Left posterior hemiblock

33. QT INTERVAL
• Measure from start of QRS to end of T wave
• It varies with rate
• Calculate corrected QT: QTc=QT/⏌RR =0.38–0.42s
• Prolonged QT interval: acute myocardial ischaemia,
myocarditis, bradycardia, U&E imbalance (Hypokalemia,
Hypocalcemia, Hypomagnesemia)

34. ST SEGMENT
• Usually isoelectric
• ST elevation (>1mm) usually implies infarction
• ST depression (>0.5mm) usually implies ischemia, NSTEMI

36. T-WAVE
• Normally inverted in aVR, V1 and occasionally V2
• Abnormal if inverted in I, II, and V4–V6
• Peaked in hyperkalaemia and flattened in hypokalaemia

37. NORMAL ECG
• Standardization – 10 mm (2 boxes) = 1 mV
• Sinus Rhythm – Each P followed by QRS, R-R constant
• P waves – always examine for in L2, V1, L1
• QRS positive in L1, L2, L3, aVF and aVL. – Neg in aVR
• QRS is < 0.12 narrow, Q in V5, V6 < 0.04, < 2 mm deep
• R wave progression from V1 to V6, QT interval < 0.4
• Axis normal – L1, L3, and aVF all will be positive
• ST Isoelectric, T waves ↑, Normal T↓ in aVR,V1, V2

38. NORMAL VARIATIONS
• May have slight left axis due to rotation of heart
• May have high voltage QRS – simulating LVH
• T inversions in V2, V3 and V4 – Juvenile T ↓
• Similarly in women also T↓
• Low voltages in obese women and men
• Non cardiac causes of ECG changes may occur

39. THANK YOU