Electrocardiogram (ECG)
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
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
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
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
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
V1 – right of sternum V2 – left of sternum V3 - midway between positions for V2
and V4 V4 - left midclavicular line
Anatomical Locations
V5 - Horizontal level of V4 at left anterior axillary line
V6 – horizontal level of V4 at left midaxillary line
Standard Limb Leads
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
Augmented – need to amplify the voltage to get a tracing of the same magnitude as Leads 1,2,3
Augmented
aVR - Augmented Voltage Right Arm– *RA and (LA-LL) angle -150
aVL - Augmented Voltage Left Arm– *LA and (RA-LL) angle -30
aVF - Augmented Voltage Left Foot– *LL and (RA-LA) angle +90
Leads
II, III, and AVF - inferior lead– view of inferior surface of heart
I and AVL - left lateral leads– view of left lateral wall of heart
AVR - loner
Structures of the Heart
SA Node Atria AV Node Common Bundle Right and Left Bundle Branches Purkinje fibers Ventricles
Electrical Events
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
6. Impulse crosses the intraventricular septum from left to right
7. Depolarization of ventricles simultaneously
ECG Waverforms
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
QRS - ventricular depolarization– first deflection down is Q– first deflection up is R– first downward deflection following an
upward deflection is S
Waves
ST segment - a straight line connecting two waves– ventricular isoelectric period– time from end of ventricular depolarization
to the start of ventricular repolarization T wave - ventricular repolarization
Depolarization
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
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)
Leads and the P wave
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 Minor and significant changes in P-
wave 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
Minimal shortening of the QRS duration Depression of the J point Rate-related shortening of the QT
interval
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