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Basic of ECG and Easy Interpretation
1. BASICS OF ELECTROCARDIOGRAPHY
Dr Mushfiq Newaz Ahmed
Medical Officer
Department Of Anaesthesia,
Comilla Medical College & Hospital
2. OUTLINE
1. Review of the conduction system & Action Potential
2. ECG leads and recording
3. ECG waveforms and intervals
4. Normal ECG and its variants
5. Basic Interpretation Steps of ECG
6. Arrhythmia & ECG
7. MI & ECG
8. EI & ECG
9. Thyroid Disorder & ECG
10. Emergency ECG
7. WHAT IS AN ECG?
An ECG is the recording (gram) of the
electrical activity(electro) generated
by the cells of the heart(cardio) that
reaches the body surface.
10. ECG 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)
11. ECG LEADS
The standard ECG 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
24. Localising the arterial territory
Inferior
II, III, aVF
Lateral
I, AVL,
V5-V6
Anterior /
Septal
V1-V4
25. SPECIAL SITUATION
Amputation or burns or bandages should be placed
as closely as possible to the standard sites
Dextrocardia right & left arm electrodes should be rev
ersed
pre-cordial leads should be recorded from V1R(V2) to V6
26. OTHER PRACTICAL POINTS
Effective contact between electrode and skin is essential.
Electrical Artifacts: external or internal
-External can be minimized by straightening the lead
wires
-Internal can be due to muscle tremors, shivering ,
hiccups
28. ECG PAPER BASICS
ECG graphs:
– Small Square
-Height 1 mm and width 0.04 s
– Large Square
-Height 5 mm and width 0.04X5=0.2s
Paper Speed:
– 25 mm/s( As 0.2 s=5 mm,1 s=25 mm)
Voltage Calibration:
– 1 mV= П 10 mm( 10 small square)
Half strength 5mm/mV
Double strength 20 mm/mV
33. P WAVE
Denotes Atrial depolarization
Shape-Rounded, neither peaked nor notched
Width/Duration-2.5 small sq
Height-2.5 small sq
Better seen in Lead II/Lead V1
Upright in every lead except aVR
May be Biphasic in lead V1(Equal upward and downward
deflection)
34. PR INTERVAL
Distance between onset of P wave to the beginning of Q
wave(in absence of Q wave beginning of R wave)
Denotes time interval impulse travelling from SA node to
Ventricular muscle through AV node
Normal Range:3 to 5 small Sq
Short if ‹3 small sq and long if ›5 small sq
35. NORMAL QRS COMPLEX
Denotes Ventricular depolarization
Normal width of QRS-2 to ‹3 small sq
Narrow complex if less than 2 small sq and Broa
d Complex if more than or equal to 3 small sq
36. COMPONENT OF QRS COMPLEX
o Q wave-width 1 small sq and depth 2 small sq and ‹25%
of following R wave
(Pathological if width›1 small sq,depth›2 small sq and
›25% of following R Wave)
o R wave height varies, but must remember the thing that
R wave progresses from V1 to V6(2-3 small square to les
than 25 small sq/5 large sq)
(Pathological if height›25 small sq/5 large sq)
o S wave follow R wave, depth varies,progressively
diminishes from V1 to V6
37.
38. T WAVE
Same direction as the preceding QRS complex
Blunt apex with asymmetric limbs
Height < 5 small sq in limb leads and <10 small square in
precordial leads
Smooth contours
May be tall in athletes
39. ST SEGMENT
Merges smoothly with the proximal limb of the T wave
No true horizontality
40. QT INTERVAL
Distance between beginning of QRS to the end Of T wav
e
Reciprocal relation with heart rate
Normal 8-‹11 small sq
If arrhythmia is present( HR less than 60 or more than 1
00 bpm) then QT interval should be corrected.
Corrected QT(QTc)=QT/√RR
41. U WAVE
Best seen in midprecordial leads
Height < 10% of preceding T wave
Isoelectric in lead aVL (useful to measure QTc)
Rarely exceeds 1 small sq in amplitude
May be tall in athletes (2 small sq)
44. RULE OF 300
Take the number of “Large Square” between neighboring
QRS complexes, and divide this into 300. More accuracy can
be achieved if the number of “small square” between
neighboring QRS complexes divided into 1500
Although fast, this method only works for regular rhythms.
45. RULE OF 300
It may be easiest to memorize the following table:
Number of larg
e square
Rate
1 300
2 150
3 100
4 75
5 60
6 50
7 43
46. 10 TIMES/20 TIMES RULE
Count the number of R in 30 large square(equivalent
to 6 second) and multiply it by 10 would become rate in
60 sec.
If small strip-counting the number in 15 large square
(equivalent to 3 second) and multiply it by 20
This method works well for irregular rhythms.
48. AXIS DETERMINATION
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)
49. THE QRS AXIS
By near-consensus, the norm
al QRS axis is defined as ran
ging 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)
51. THE QUADRANT METHOD
Examine the QRS complex in lead I/lead aVL and lead III/lead aVF
to determine if they are predominantly positive or predominantly
negative. The combination should place the axis into one of the 4
quadrants below.
52.
53. COMMON CAUSES OF LAD
May be normal in the elderly and very obese
Due to high diaphragm during pregnancy or ascites
Inferior wall MI
Left Anterior Hemi block
Left Bundle Branch Block
Emphysema
54. COMMON CAUSES OF RAD
Normal variant
Right Ventricular Hypertrophy
Anterior MI
Right Bundle Branch Block
Left Posterior Hemiblock
57. NORMAL SINUS RHYTHM
Originates in the sinus node
Rate between 60 and 100 beats per min
Monomorphic P waves
Normal relationship between P and QRS
Some sinus arrhythmia is normal
61. STEP-1:LEAD POSITION
Normal-P wave upright in lead I & II and QRS should be
downward in aVR & V1, R wave progresses from V1 to
V6(height increases)
Lead Malposition-P wave downward in lead I & II and QRS
should be upright in aVR & V1, R wave progresses from
V1 to V6(height increases)
Dextrocardia- P wave downward in lead I & II and QRS
should be upright in aVR & V1, R wave regresses from
V1 to V6(height decreases)
63. STEP 2: VOLTAGE OR AMPLITUDE
Normal ECG paper- voltage or amplitude 10 mV
Half Voltage,5 mV used specially when severe LVH causes very
large QRS complex which merges with QRS complexes of above
or below leads
64. Electrical Alternans-Alternate beat variation in direction,
amplitude and duration of any component of ECG. It can be
found in-Pericardial Effusion, Pericardial Mesothelioma,
Pericardial TB, Myocarditis, Hypothermia
65. STEP 3:RHYTHM & RATE
Rhythm Assessment- By Paper & Pencil Method or
Caliper Method
Rate Measurement-By 300 times method/20 times
method
66. STEP 4: AXIS
Normal- QRS of lead I(+aVL) and QRS of lead II+(III &
aVF) is in the same direction
LAD- QRS of lead I(+aVL) upward and QRS of lead II+(III
& aVF) downward
RAD- QRS of lead I(+aVL) downward and QRS of lead
II+(III & aVF) upward
69. STEP 5: BUNDLE BRANCH BLOCK
(CLUE: WIDE QRS)
RBBB- M pattern in QRS in Lead V1( or V2/V3). May be
normal
LBBB-M pattern in QRS in Lead V6( or V4/V5). T inversion can
be found. New onset always Alarming
Bifascicular block-
RBBB+ Left posterior Hemiblock----›features of
RBBB+RAD(Ostium Secundum ASD)
RBBB+ Left anterior Hemiblock ----›features of
RBBB+LAD(Ostium Primum ASD)
71. STEP 6:CHAMBER ENLARGEMENT
Right Atrial Enlargement- Tall peaked P wave
Left Atrial Enlargement-Broad/M Pattern/Wide/Bifid or
notched P wave
Right Ventricular Enlargement-Tall R in V1 and deep S in
V5/V6
Left Ventricular Enlargement-Unusually tall R in V5/V6
and unusually deep S in V1(R+S>35 mm)
119. POSTERIOR MI
ST depression in V2-V3
Tall, Broad R wave in V2-V3
Dominant R wave in V2(R>S)
Upright T wave
120. Posterior MI confirmed by posterior lead V7, V8, V9
V7=Left Post. Axillary line, same plane to V6
V8=Tip of the scapula
V9=Left Paraspinal line
121. Same case with posterior lead
ST segment elevation in V7-V9
122. DIFFERENCE BETWEEN MI AND ACUTE
PERICARDITIS
ST shape-Convex Up
Location of ST change-
Territorial
Reciprocal ST change-
Present
Q wave change-May be
Present
ST shape-Concave up
Location of ST change-
Limb & Precordial
Reciprocal ST change-
Absent
Q wave change-Absent
Acute MI Acute Pericarditis
If the three limbs of triangle broken apart, collapsed and superimposed over the heart, then positive electrode for lead I=0º,lead II=60º,lead III=120º in relation to heart
Single positive electrode that is referenced against a combination of other limb electrodes. Positive electrodes for LA=aVL, RA=aVR, LL=aVF
V1-Right 4th ICS,V2-Left 4th ICS,V4-5th ICS in left MCL, V3-In between V2 & V4, V5-Left 5th ICS in AAL, V6-Left 5th ICS in MAL
V1-V2=Septal or Anteroseptal( Right Ventricular), V3-V4=Anterior or Anteroapical, V5-V6= Anterolateral or lateral( Left ventricular)