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Elec 331 - EKG, EEG & EMG
Definitions
• Electro – Kardio / Cardio – Gram
– Graphic record (gram) of electrical (electro) heart activity (cardio)
– EKG
• Germanic
– ECG
• Romantic
• Lead
– Voltage measurement (not a physical probe)
– Unipolar (PD between electrode & physical or virtual ground)
– Bipolar (PD between two electrodes)
Einthoven’s Triangle
• Electrodes
– RA, LA, LL
– RL, C = reference
RA
LA
• 3 Bipolar Leads
C
– I, II, III
• 3 Unipolar Leads
– aVR, aVL, aVF
• Approximated by an
EQUILATERAL
triangle
RL
LL
SRC: PNP, p.408
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Elec 331 - EKG, EEG & EMG
Lead = Projection of Cardiac Vector
(unit vector)
r
r
VI  VI u I
RA
r
M
LA

ur
r
r
V I  Projection of M onto uI
r r
r
VI  M  uI  M cos 
ur
r
V I  VI uI
Y-axis of EKG
(X-axis = time)
LL
Wilson’s Central Terminal
I
RA
VR
LA
VL
CT
II
VF
III
LL
CT = Measured (direct) or Average of RA, LA & LL (indirect)
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Elec 331 - EKG, EEG & EMG
6-Lead EKG (5 Electrodes)
• Bipolar
• Unipolar
– Convention makes signal
positive for cardiac vector
pointed toward apex (LL) or
left ventricle (LA)
– Reference is augmented
version of Wilson’s Central
Terminal
– aVR
– Lead I
• Augmented Voltage at
Right arm
• V(LA) – V(RA)
– aVL
– Lead II
• Augmented Voltage at Left
arm
• V(LL) – V(RA)
– Lead III
– aVF
• V(LL) – V(LA)
• Augmented Voltage at left
Foot
Augmented Unipolar Leads
(same direction – larger magnitude)
RA
VL
LA
RA
LA
aVL
LL
LL
VL  LA  mean( RA, LA, LL)
aVL  LA  mean( RA, LL)
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Elec 331 - EKG, EEG & EMG
Limb Leads (Coronal Plane)
LA
RA
≈30° between
lead vectors
LL
12-Lead EKG
Precordial Leads (Transverse Plane)
≈15° between
lead vectors
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Elec 331 - EKG, EEG & EMG
6-Lead EKG
• P Wave
– Firing of SA node
– Atrial depolarization
• QRS Complex
– Firing of AV node
– Ventricular depolarization
• T Wave
– Ventricular repolarization
• Bandwidth ≈ 150Hz (American Heart Assoc.)
Electroencephalogram (EEG)
Abilities
Thought Processes
Scientific Skills
Number Skills
Reasoning
Language
Right Hand
Left Brain
Art & Music
Imagination
3-D Forms
Insight
Left Hand
Right Brain
5
Elec 331 - EKG, EEG & EMG
Organs
Sensory
Motor
SRC: PNP, p.114, 116
EEG Electrodes
75 Electrodes
6
Elec 331 - EKG, EEG & EMG
EEG Frequency Spectrum




Relaxed
(eyes closed)
Amplitude
Asleep

Drowsy
6 Seconds
 

Active
Motion

Concentrating
Frequency (Hz)
Epileptic Seizure
Partial
General
7
Elec 331 - EKG, EEG & EMG
Electromyogram (EMG)
• Muscle Cell
Depolarization
• Excitation / Contraction
Coupling
SRC: PNP, p.278
EMG Data Processing
Bandwidth ≈ 20 Hz
Raw Data (Lifting Exercise)
DC Offset Removed
Rectified
LP Filtered
Integrated (Effort / Motion)
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