Electocardiogram presentation

1. The Electrocardiogram
Sanju Sah
St. Xavier’s college, Maitighar
1

2. Electrocardiogram
• An electrocardiogram is a tracing of the
heart’s electrical activity
• An electrocardiograph is the machine that
produces it

3. Electrocardiograph
• Also called the ECG
machine, it detects
heart’s electrical activity
through electrodes
positioned on patient’s
skin
• Lead wires transfer
electrical activity back to
ECG machine where it is
displayed or printed onto
graph paper.

6. Lead wire and electrodes
• Lead wires and cables
transfer the ECG signal
detected through the
electrodes to the ECG
machine
– There may be 3, 4, or 5
lead wires for monitoring
purposes and up to 10 lead
wires for 12-lead ECGs
– Each lead wire has a
labeled clip, snap, or pin-
type connector on the
distal end which attaches
to the electrode

7. ECG Leads
• Are a combination of electrodes that form an
imaginary line in the body along which the
electrical signals, detectable during the time
course of the heartbeat, are measured
• Each lead provides a different view of the heart:
– Electrodes are placed on chest, arms and legs
– Sites vary depending on which view of the heart's
electrical activity is being assessed
• ECG leads are either bipolar or unipolar

8. Bipolar Leads
• Record the flow of
the electrical
impulse between
two (one is positive,
the other is
negative) selected
electrodes
• Includes I, II and III

10. Unipolar Leads
• Use only one
positive electrode
and a reference
point calculated by
the ECG machine
• Includes leads aVR,
aVL, aVF, and V1
through V6

11. • Electrodes are placed
on the extremities and
chest wall to view the
heart’s electrical
activity from the
frontal and horizontal
planes
– Provides a cross-
sectional view of the
heart

14. Graphical representation of Einthoven's triangle

15. » RA (Right Arm) -
Anywhere between the
right shoulder and right
elbow
» RL (Right Leg) - Anywhere
below the right torso and
above the right ankle
» LA(Left Arm) - Anywhere
between the left shoulder
and the left elbow
» LL (Left Leg) - Anywhere
below the left torso and
above the left ankle

16. • » V1 - Fourth intercostal
space on the right
sternum
» V2 - Fourth intercostal
space at the left sternum
» V3 - Midway between
placement of V2 and V4
» V4 - Fifth intercostal
space at the
midclavicular line
» V5 - Anterior axillary
line on the same
horizontal level as V4
» V6 - Mid-axillary line
on the same horizontal
level as V4 and V5

17. Effects of artifact on ECG recording
• Interference from the power line
• Shifting of baseline
• Muscle Tremor

19. Type of ECG recorders
• Single/ Three/ Six/ Twelve channel ECG
recorder
• channel ECG recorder
• ECG system for Stress Testing
• Holter recording

21. ELECTROENCEPHALOGRAPHY
(EEG)

22. Introduction
• Electroencephalography is a technique that
records the electrical activity of the brain
• The recording of the brains spontaneous
electrical activity is done over a short period
of time, usually 20–40 minutes, as recorded
from multiple electrodes placed on the scalp.

23. • Electroencephalograph is an instrument used for
recording of electrical activity of brain.
• The activity measured by EEG are electrical
potential created by the post-synaptic currents.
• Its an effective method for diagnosing many
neurological disorder such as epilepsy,
tumour,etc.

24. Principle
• The brains electrical charge is maintained by
billions of neurons.
• Neurons pass signals via action potential created
by exchange between sodium and potassium ions
in and out of the cell - Volume conduction.
• When the wave of ions reaches the electrodes on
the scalp, they can push or pull electrons on the
metal on the electrodes, the difference in push,
or voltage, between any two electrodes can be
measured by a voltmeter. Recording these
voltages over time gives us the EEG.

25. • Scalp EEG activity shows oscillations at a variety
of frequencies. Several of these oscillations have
characteristic frequency ranges, spatial
distributions and are associated with different
states of brain functioning.

26. Brain Wave Classification
• Brain patterns form wave shapes that are commonly
sinusoidal.
• Measured from peak to peak and normally range from
0.5 to 100 μV in amplitude.
• Signal is derived by means of Fourier transform power
spectrum from the raw.
• Brain waves have been categorized into four basic
groups;
- Beta (>13 hz)
- Alpha (8-13 hz)
- Theta (4-8 hz)
-Delta (0.5-4 Hz)

27. Applications
• Monitor alertness, coma and brain death
• Locate areas of damage following head injury,
stroke, tumor, etc.
• Test afferent pathways (by evoked potentials)
• Control anesthesia depth
• Investigate epilepsy and locate seizure origin
• Test epilepsy drug effects

28. Methodology
• Non-invasive and painless
• Major components;
– 1. Electrodes with conductive media
– 2. Amplifiers with filters
– 3. A/D converter
– 4. Recording device
• Electrodes read the signal from the head surface,
amplifiers bring the microvolt signals into the range
where they can be digitalized accurately, converter
changes signals from analog to digital form and
computer stores and displays obtained data.

29. Recording electrodes
• Types of electrodes:
1. Disposable (gel-less, and pre-gelled types)
2. Reusable disc electrodes (gold, silver, s.s. or tin)
3. Headbands and electrode caps
4. Saline-based electrodes
5. Needle electrodes
• Electrode caps are preferred, with certain number of
electrodes installed on its surface.
• Commonly used scalp electrodes consist of Ag-AgCl disks, 1 to
3 mm in diameter, with long flexible leads that can be plugged
into an amplifier.
• Needle electrodes are used for long recordings and are
invasively inserted under the scalp.

30. • Electrode locations and names are specified by the
International 10–20 system for most clinical and research
application
• Label 10-20 designates proportional distance in percents
between ears and nose where points for electrodes are
chosen.
• Electrode placements are labeled according adjacent brain
areas: F (frontal), C (central), T (temporal), P (posterior),
and O (occipital).
• The letters are accompanied by odd numbers at the left
side of the head and with even numbers on the right side.
• In general 25 electrodes are used in general EEG test but no
of electrode may vary as per the EEG requirement and area
of investigation In 25 electrode EEG system
– 23 electrode are active electrodes
– 1 is ground electrode
– 1 is ref electrode

31. Labels for points according to 10-20
electrode placement system

33. • Display of the EEG may be set up in one of
several ways. The representation of the EEG
channels is referred to as a montage.
1. Bipolar montage: Each channel (i.e., waveform)
represents the difference between two adjacent
electrodes. The entire montage consists of a series of
these channels.
2. Referential montage: Each channel represents the
difference between a certain electrode and a
designated reference electrode.
3. Average reference montage: The outputs of all of
the amplifiers are summed and averaged, and this
averaged signal is used as the common reference for
each channel.
4. Laplacian montage: Each channel represents the
difference between an electrode and a weighted
average of the surrounding electrodes.

34. Amplifiers and filters
• The input signal to the amplifier consists of five
components:
1.Desired biopotential
2.Undesired biopotential
3.A power line interference signal of 50/60 Hz and its harmonics
4.Interference signals generated by the tissue/electrode interface
5.Noise
• The A/D converter is interfaced to a computer system so
that channels of analog signal are converted into a digital
representation.
• Analog low-pass filters prevent distortion of the signal by
interference effects with sampling rate, called aliasing,
which would occur if frequencies greater than one half of
the sampling rate survive.

35. Artifacts
• Among basic evaluation of the EEG traces belongs
scanning for signal distortions called Artefacts.
• The Artefact in the recorded EEG may be either patient-
related or technical.
• Patient related: Technical:
– Any minor body movements - 50/60 hz
– EMG - Impedance fluctuation
– ECG (pulse, pace-maker) - Cable movements
– Eye movements - Broken wire contacts
– Sweating - Too much electrode paste/jelly
- Low battery

36. Evoked potentials
• Evoked potentials are used to measure the electrical
activity in certain areas of the brain and spinal cord.
Electrical activity is produced by stimulation of specific
sensory nerve pathways.
• Types of evoked potentials
– Visual Evoked Potentials (VEP): the patient sits before a
screen in which alternating patterns are displayed.
– Auditory Evoked Potentials (AEP): the patient listens to a
series of clicks in each ear.
– Sensory Evoked Potentials (SEP): short electrical impulses
are administered on the arm or leg.
– Motor Evoked Potentials: these can detect disruption on a
motor pathway of the brain or spinal cord.

38. ELECTROMYOGRAM

39. INTRODUCTION
• Electromyogram (EMG) is a technique for
evaluating and recording the electrical activation
signal of muscles.
• EMG is performed by an electromyograph, which
records an electromyogram.
• Electromyograph detects the electrical potential
generated by muscle cells when these cells contract
and relax.

40. EMG Apparatus Muscle Structure/EMG

41. EMG PROCEDURE
• Clean the site of application
of electrode;
• Insert needle/place surface
electrodes at muscle belly;
• Record muscle activity at rest;
• Record muscle activity upon
voluntary contraction of the
muscle.

42. EMG Contd.
• Muscle Signals are
Analog in nature.
• EMG signals are also
collected over a
specific period of
time.
Analog Signal

43. EMG Contd.
EMG processing:
Amplification
& Filtering
Signal pick up
Conversion of Analog
signals to Digital signals
Computer

44. Types of EMG
• Electrode Categories
– Inserted
• Fine-wire (Intra-muscular)
• Needle
– Surface

45. EMG Electrodes
Fine wire
Surface
Electrodes
Needle
electrode

46. Fine-wire Electrodes
• Advantages
– Extremely sensitive
– Record single muscle activity
– Access to deep musculature
– Little cross-talk concern
• Disadvantages
– Extremely sensitive
– Requires medical personnel, certification
– Repositioning nearly impossible
– Detection area may not be representative of entire muscle

47. Surface Electrodes
• Advantages
– Quick, easy to apply
– No medical supervision, required certification
– Minimal discomfort
• Disadvantages
– Generally used only for superficial muscles
– Cross-talk concerns
– No standard electrode placement
– May affect movement patterns of subject
– Limitations with recording dynamic muscle activity

48. General Concerns
• Signal-to-noise ratio
– Ratio of energy of EMG signal divided by energy of
noise signal
• Distortion of the signal
– EMG signal should be altered as minimally as
possible for accurate representation

49. Characteristics of EMG Signal
• Amplitude range: 0–10
mV (+5 to -5) prior to
amplification
• Useable energy: Range
of 0 - 500 Hz
• Dominant energy: 50 –
150 Hz

50. Characteristics of Electrical Noise
• Inherent noise in electronics equipment
• Ambient noise
• Motion artifact
• Inherent instability of signal

51. Inherent Noise in Electronics
Equipment
• Generated by all electronics equipment
• Frequency range: 0 – several thousand Hz
• Cannot be eliminated
• Reduced by using high quality components

52. Ambient Noise
• Electromagnetic radiation sources
– Radio transmission
– Electrical wires
– Fluorescent lights
• Essentially impossible to avoid
• Dominant frequency: 60 Hz
• Amplitude: 1 – 3x EMG signal

53. Motion Artifact
• Two main sources
– Electrode/skin interface
– Electrode cable
• Reducible by proper circuitry and set-up
• Frequency range: 0 – 20 Hz

54. Inherent Instability of Signal
• Amplitude is somewhat random in nature
• Frequency range of 0 – 20 Hz is especially
unstable
• Therefore, removal of this range is
recommended

55. Solutions for Signal Interruption Related to
Electrode and Amplifier Design
• Differential amplification
– Reduces electromagnetic radiation noise
– Dual electrodes
• Electrode stability
– Time for chemical reaction to stabilize
– Important factors: electrode movement, perspiration,
humidity changes
• Improved quality of electrodes
– Less need for skin abrasion, hair removal

56. Differential Amplification
• Ambient
(electromagnetic) noise
is constant
• System subtracts two
signals
• Resultant difference is
amplified
• Double differential
technique

57. Electrode Placement
• Away from tendon
– Fewer, thinner muscle fibers
– Closer to other muscle origins, insertions
• More susceptible to cross-talk
• Away from outer edge of muscle
– Closer to other musculature
• Orientation parallel to muscle fibers
– More accurate conduction velocity
– Increased probability of detecting same signal

58. EMG Electrode Placement

59. Surface Electrode Placement

60. Reference Electrode Placement
(Ground)
• As far away as possible from recording
electrodes
• Electrically neutral tissue
– Bony prominence

61. APPLICATION OF EMG
• EMG can be used for diagnosis of Neurogenic
or Myogenic Diseases.