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Flashcards in ECG Deck (21)
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Electrical activity causes...

Mechanical activity SO electrical activity happens first


2 speeds

1mm=0.02 sec


1 or the other



Monitoring heart at different angles

Each different angle/pair of electrodes = LEAD

Each lead = + & - electrode

3 lead systems


How to place leads

Place patient in right lateral recumbancy = put on right side

Attach electrodes to skin proximal to elbows and stifles

Wet electrodes with alcohol

Check speed, amplitude and other setting and calibration

Attach negative electrode to one limb and positive to the other limb


3 bipolar Bipolar limb heads

Measure current from negative to positive electrode

Measuring same electrical activity but from different angles

Lead I = RA to LA
Lead II = RA to LL
Lead III = LA to LL
Grounding Lead = RL


Unipolar Limb Leads

Same leads at bipolar limb leads
3 new angles

Lead aVR = + on RA
Lead aVL = + on LA
Lead aVF = + on LL


Chest leads...

Record electrical activity from dorsal and ventral surface of the heart

RA, LA, and LL are connected to form a 0 reference at the center of the heart

ECG records voltage from heart to selected electrode on chest


Axis of leads

Direction (degree) from negative to positive


Einthoven's Triangle

Tells you direction of the bipolar leads


Axis of Leads

- to +

Lead I = 0 degrees b/c horizontal impulse
Lead II = 60 degrees
Lead III = 120 degrees

Lead aVR = 210 or -150
Lead aVL = -30
Lead aVF = 90


Why are some waves positive and others negative?



Reading ECG

Impulses toward + electrode = upward deflection on ECG

Impulses from - electrode = downward deflection

Impulse traveling perpendicular to lead = ISOELECTRIC TRACING = electrical forces are equal

no electrical activity = BASELINE TRACING = tissue is fully depolarized or repolarized


P Wave
QRS Wave
T Wave

Atrial Dep
Ventricular Dep
Ventricular Rep


P wave

Atrial Depolarization
SA Node to atria = impulse that is downward and to the left
Upward + deflection in Lead I (horizontal to the left) and Lead aVF (vertical downward)


After P wave

Baseline Tracing bc atria dep and ventricals are still rep as impulse moves through AV node


QRS Wave

Ventricular Depolarization

wave goes in 3 diff direction bc amount of tissue depolarizing changes as electrical impulse moves through the heart

Septal Dep
Apical Dep
Late Ventrical Dep


Septum Depolarization

Right and Downward

Small downward deflection in Lead I (Q wave) and positive deflection in Lead aVF (R wave)

not a lot of current bc not a lot of tissue


Apical Depolarization

apical ventricular myocardium

Downward and to the left

Large positive upward deflection (R wave) in Lead I
extend R wave in lead aVF


Late Ventricular Depolarization

Upward and to the left

Extends r wave in Lead I
downward deflection in Lead aVF (S wave)


ST Segment

End of S wave to the beginning of T wave

when vents completely dep = no current bc atria rep and vent dep


Ventricualr depolarization

Cells rep based on length of action potential

Epicardium rep first and creates a current in the same direction as dep
Endocardium rep after

T wave in same direction as major wave of QRS

Pos in Lead I