Resting ECG

An overview

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

Generally standard procedure to monitor and record the ECG during a graded exercise test (GXT)

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)

PHASES OF THE RESTING ECG

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

Time and Voltage

Duration - seconds Amplitude - millivolts Configuration - shape and appearance

EKG Paper

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