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Basics of ECG for Technicians
1. DR. PALLAB KANTI NATH
MBBS, MD (ANESTHESIOLOGY)
CONSULTANT PAIN MEDICINE, ANESTHESIOLOGIST,
INTENSIVIST
Basics of Electrocardiography for
Technicians
2. What will we learn?
1. Basics of the conduction system of heart
2. ECG leads and recording methodology
3. ECG waveforms and intervals
4. Normal ECG and its variants
5. Interpretation and reporting of an ECG
3.
4. What is an ECG?
Recording of the electrical activity heart.
Graph of voltage versus time
6. BasicsBasics
ECG graph:
1 mm Small squares
5 mm Large squares
Paper Speed:
25 mm/sec standard
Voltage Calibration:
10 mm/mV standard
7. ECG Paper: DimensionsECG Paper: Dimensions
5 mm
1 mm
0.1 mV
0.04 sec
0.2 sec
Speed = rate
Voltage
~Mass
8. ECG Leads
Leads are electrodes which measure the potential
difference between:
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)
9. ECG Leads
The standard ECG has 12 leads: 3 Standard Limb Leads
3 Augmented Limb Leads
6 Precordial Leads
12. Electrode name Electrode placement
RA On the right arm, avoiding thick muscle.
LA On the left arm, avoiding thick muscle.
RL On the right leg, lateral calf muscle.
LL On the left leg, lateral calf muscle.
V1
In the fourth intercostal space (between ribs 4 and 5) just
to the right of the sternum (breastbone).
V2
In the fourth intercostal space (between ribs 4 and 5) just
to the left of the sternum.
V3 Between leads V2 and V4.
V4 5th Intercostal space at the midclavicular line
V5 Anterior axillary line at the same level as V4
V6 Midaxillary line at the same level as V4 and V5
16. Overdamping and Underdamping
Overdamping: When the pressure of the stylus is too firm
on the paper so that it’s movements are retarded –
deflection fractionally wider and diminished amplitude
Unerdamping: When the writing stylus is not pressed
firmly enough against the paper - sharp spikes at the
corners
22. Artefacts on ECG
Distorted signals caused by secondary internal or external
sources, such as muscle movement or interference from an
electrical device.
23. ECG Artefacts
ECG tracing is affected by patient’s motion.
rhythmic motions (shivering or tremors) can create
the illusion of arrhythmia.
May lead to:
Altered diagnosis, treatment, outcome of
therapy and legal liabilities
24. Reducing Artefacts during an ECG
Patient Positioning
Supine or semi-Fowler’s position.
If patient can’t tolerate lying flat, do the ECG in a more upright
position.
Instruct patient to place arms down by his side and
to relax the shoulders.
Patient’s legs should be uncrossed.
Place electrical devices, such as cell phones, away
from the patient as they may interfere with the
machine.
25. Reducing Artefacts during an ECG
Skin Preparation
Dry the skin if it’s moist or diaphoretic.
Shave any hair that interferes with electrode
placement.
ensures a better electrode contact with the skin.
Rub an alcohol prep pad or benzoin tincture on the
skin to remove any oils and help with electrode
adhesion.
26. Reducing Artefacts during an ECG
Electrode Application
Check the electrodes to make sure the gel is still
moist.
Do not place the electrodes over bones.
Do not place the electrodes over areas where there is
a lot of muscle movement.
27. Interpretation of an ECG
Heart Rate
Rhythm
Axis
Wave morphology
Intervals and segments analysis
Specific changes (If any)
30. Rule of 300
Take the number of “big boxes” between neighboring
QRS complexes, and divide this into 300. The result
will be approximately equal to the rate
Although fast, this method only works for regular
rhythms.
31. The Rule of 300
It may be easiest to memorize the following table:
# of big# of big
boxesboxes
Rate (appx)Rate (appx)
11 300300
22 150150
33 100100
44 7575
55 6060
66 5050
33. 10 Second Rule
As most ECGs record 10 seconds of rhythm per
page, one can simply count the number of beats
present on the ECG and multiply by 6 to get the
number of beats per 60 seconds.
This method works well for irregular rhythms.
34. 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)
35. 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)
38. The Quadrant Approach
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.
39. Using leads I, II, III
LEAD 1LEAD 1 LEAD 2LEAD 2 LEAD 3LEAD 3
NormalNormal UPRIGHTUPRIGHT UPRIGHTUPRIGHT UPRIGHTUPRIGHT
PhysiologicaPhysiologica
l Left Axisl Left Axis
UPRIGHTUPRIGHT
UPRIGHT /UPRIGHT /
BIPHASICBIPHASIC
NEGATIVENEGATIVE
PathologicalPathological
Left AxisLeft Axis
UPRIGHTUPRIGHT NEGATIVENEGATIVE NEGATIVENEGATIVE
Right AxisRight Axis NEGATIVENEGATIVE
UPRIGHTUPRIGHT
BIPHASICBIPHASIC
NEGATIVENEGATIVE
UPRIGHTUPRIGHT
ExtremeExtreme
Right AxisRight Axis
NEGATIVENEGATIVE NEGATIVENEGATIVE NEGATIVENEGATIVE
40. Common causes of LAD
May be normal in the elderly and very obese
High diaphragm during pregnancy, ascites, or Abdominal
tumors
Inferior wall MI
Left Anterior Hemiblock
Left Bundle Branch Block
WPW Syndrome
Emphysema
41. Common causes of RAD
Normal variant
Right Ventricular Hypertrophy
Anterior MI
Right Bundle Branch Block
Left Posterior Hemiblock
WPW Syndrome
42. Normal Sinus Rhythm
Originates in the SA node
Rate between 60 and 100 beats per min
Tallest p waves in Lead II
Monomorphic P waves
Normal PR interval of 120 to 200 msec
Normal relationship between P and QRS
Some sinus arrhythmia is normal
43. Normal QRS complex
Completely negative in lead aVR , maximum positivity in
lead II
rS in right oriented leads and qR in left oriented leads
(septal vector)
Transition zone commonly in V3-V4
RV5 > RV6 normally
Normal duration 50-110 msec, not more than 120 msec
Physiological q wave not > 0.03 sec
45. Amplitude of QRS
Formed by electrical force generated by the
ventricular myocardium
Depends on:
distance of the sensing electrode from the
ventricles
Body build - a thin individual has larger
complexes when compared to obese individuals
46. Normal T wave
Same direction as the preceding QRS complex
Blunt apex with asymmetric limbs
Height < 5mm in limb leads and <10 mm in
precordial leads
Smooth contours
May be tall in athletes
47. QT interval
The beginning of the QRS complex is best determined in a
lead with an initial q wave
leads I,II, avL ,V5 or V6
QT interval shortens with tachycardia and lengthens with
bradycardia
Normal 350 to 430 msec
With a normal heart rate (60 to 100), the QT interval
should not exceed half of the R-R interval roughly
Limb leads: Leads I, II and III are called the limb leads. The electrodes that form these signals are located on the limbs—one on each arm and one on the left leg. The limb leads form the points of what is known as Einthoven&apos;s triangle.
Augmented limb leads: Leads aVR, aVL, and aVF are the augmented limb leads. They are derived from the same three electrodes as leads I, II, and III, but they use Goldberger&apos;s central terminal as their negative pole which is a combination of inputs from other two limb electrodes.
Precordial leads: The precordial leads lie in the transverse (horizontal) plane, perpendicular to the other six leads. The six precordial electrodes act as the positive poles for the six corresponding precordial leads: (V1, V2, V3, V4, V5 and V6). Wilson&apos;s central terminal is used as the negative pole.
Einthoven&apos;s triangle is an imaginary formation of three limb leads in a triangle
It is formed by the two shoulders and the pubis.
The shape forms an inverted equilateral triangle with the heart at the center that produces zero potential when the voltages are summed
It is named after Willem Einthoven who theorized its existence