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Resting ECG
An overview
Electrocardiogram (ECG)
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Graphic recording of the electrical
activity (impulses) generated by the
heart
Placement of electrodes on the body
will allow for detection of these impulses
ECG
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Generally standard procedure to
monitor and record the ECG during a
graded exercise test (GXT)
ECG
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Equipment
– adhesive silver-silver chloride electrodes
with electrolyte gel or paste
– electrical wires
– amplifier
– monitor
– recording apparatus
– computer to program the treadmill
Twelve views of the heart
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Lead - two or more electrodes placed
on the body in designated anatomical
locations
1. Standard Limb Leads (3)
2. Augmented Limb Leads (3)
3. Chest Leads (6)
Use 10 electrodes
Anatomical Locations of Leads
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Right Arm (RA) - right shoulder below
the clavicle but above the border of
pectoralis
Left Arm (LA) - left shoulder below the
clavicle but above the border of
pectoralis (in deltoid fossa)
Anatomical Locations
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Right Leg (RL) - halfway between the
costal margin (ribs) and the iliac crest
(hip bone)
Left Leg (LL) - halfway between the
costal margin and the iliac crest
Anatomical Locations
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V1 – right of sternum
V2 – left of sternum
V3 - midway between positions for V2
and V4
V4 - left midclavicular line
Anatomical Locations
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V5 - Horizontal level of V4 at left
anterior axillary line
V6 – horizontal level of V4 at left
midaxillary line
Standard Limb Leads
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Lead 1 - *Left Arm (LA) - Right Arm (RA)
angle 0
Lead 2 - *Left Leg (LL) - Right Arm (RA)
angle 60
Lead 3 - *Left Leg (LL) - Left Arm (LA)
angle 120
– * indicates positive electrode
Augmented Limb Leads
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Augmented – need to amplify the
voltage to get a tracing of the same
magnitude as Leads 1,2,3
Augmented
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aVR - Augmented Voltage Right Arm
– *RA and (LA-LL) angle -150
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aVL - Augmented Voltage Left Arm
– *LA and (RA-LL) angle -30
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aVF - Augmented Voltage Left Foot
– *LL and (RA-LA) angle +90
Leads
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II, III, and AVF - inferior lead
– view of inferior surface of heart
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I and AVL - left lateral leads
– view of left lateral wall of heart
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AVR - loner
Structures of the Heart
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SA Node
Atria
AV Node
Common Bundle
Right and Left Bundle Branches
Purkinje fibers
Ventricles
Electrical Events
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1. Sinus Node in the atrium
2. Depolarization left, inferior, and
anterior through right atrium
3. Spreads through left atrium
4. AV node and Bundle of His
5. Left and Right Bundle Branches
Electrical Events
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6. Impulse crosses the intraventricular
septum from left to right
7. Depolarization of ventricles
simultaneously
ECG Waverforms
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P - atrial depolarization
PR interval - an interval encompasses
at least one wave plus the connecting
line
– time from start of P wave to beginning of
QRS
– time for depolarization of the atria to
beginning of ventricular depolarization
Waves
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QRS - ventricular depolarization
– first deflection down is Q
– first deflection up is R
– first downward deflection following an
upward deflection is S
Waves
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ST segment - a straight line connecting
two waves
– ventricular isoelectric period
– time from end of ventricular depolarization
to the start of ventricular repolarization
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T wave - ventricular repolarization
Depolarization
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Positive deflection - a wave of
depolarization moving toward a positive
electrode
Negative deflection - a wave of
depolarization moving away from a
positive electrode
biphasic - wave moving perpendicularly
to the positive electrode (positive
deflection precedes negative)
Repolarization
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Positive deflection - a wave of
repolarization moving away from a
positive electrode
Negative deflection - a wave of
repolarization moving toward a positive
electrode
biphasic - wave moving perpendicularly
to the positive electrode (negative
deflection precedes positive)
PHASES OF THE RESTING ECG
Leads and the P wave
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Atrial Depol wave moving toward leads
I, AVL, II, and AVF  positive deflection
Lead III biphasic
Lead AVR  negative deflection
Normal ECG Responses to
Exercise
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Minor and significant changes in Pwave
Superimposition of the P and T waves
of successive beats
Increases in Q wave amplitude
Slight decreases in R wave amplitude
Increases in T wave amplitude
Normal Responses
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Minimal shortening of the QRS duration
Depression of the J point
Rate-related shortening of the QT
interval
Time and Voltage
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Duration - seconds
Amplitude - millivolts
Configuration - shape and appearance
EKG Paper
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Light Lines (small squares)- 1mm x
1mm
Dark Lines (large squares) - 5mm x
5mm
Small square - .04 s and/or .1 mV
Large Square - .2 s and/or .5 mV