Basics of ecg

brief discussion on ECG for critical care 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

4. What is an ECG?
Recording of the electrical activity heart.
Graph of voltage versus time

5. Recording an ECG

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

10. Einthoven's triangle

11. 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.
V
1
In the fourth intercostal space (between ribs 4 and 5) just
to the right of the sternum (breastbone).
V
2
In the fourth intercostal space (between ribs 4 and 5) just
to the left of the sternum.
V
3
Between leads V
2
and V
4
.
V
4 5th Intercostal space at the midclavicular line
V
5 Anterior axillary line at the same level as V4
V
6 Midaxillary line at the same level as V4 and V5

13. Arrangement of Leads on the ECG

14. Arrangement on an ECG strip

15. Normal standardization
1 mV=10 mm
Will result in perfect right angles at each corner

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

17. Standard sites unavailableAmputation/
burns/
bandages
leads should
be placed as
closely as
possible to
the standard
sites

18. Specific cardiac abnormalities
dextrocardia right & left arm electrodes should be
reversed
pre-cordial leads should be recorded from V1R(V2)
to V6

19. Continuous monitoring
Bed side

20. Continuous monitoring
Holter monitoring

21. Continuous monitoring
TMT

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)

29. Determining the Heart Rate
Rule of 300
10 Second Rule

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

32. Rule of 300

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)

36. Determining the Axis
The Quadrant Approach
The Equiphasic Approach

37. Determining the Axis
Predominantly
Positive
Predominantly
Negative
Equiphasic

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
Pathological Pathological
Left AxisLeft Axis
UPRIGHTUPRIGHT NEGATIVENEGATIVE NEGATIVENEGATIVE
Right AxisRight Axis NEGATIVENEGATIVE
UPRIGHTUPRIGHT
BIPHASICBIPHASIC
NEGATIVENEGATIVE
UPRIGHTUPRIGHT
Extreme Extreme
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

44. QRS Complex

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

48. QT Interval

49. Reporting an ECG

50. “ WHOSE ECG IS IT ?!”
1. Patient Details

51. “IS IT PROPERLY TAKEN ?”
2. Standardisation and lead
placement

53. NORMAL OR ABNORMAL?
4. Segment and wave form
analysis

54. “ DOES THE ECG CORRELATE WITH
THE CLINICAL SCENARIO ?”
Final Impression

55. Thank you !