ECG LEADS. introduction The heart produces electrical currents The body acts as a conductor of...
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Transcript of ECG LEADS. introduction The heart produces electrical currents The body acts as a conductor of...
ECG LEADS
introduction
The heart produces electrical currents
The body acts as a conductor of electricity
Electrodes are able to measure the voltages of the cardiac current
introduction
An ECG is a recording of the electrical activity of the heart
Different “views” of the heart can be recorded with different electrodes
Inroduction
12 possible leads
Six limb (extremity) leads
Bipolar leads: I, II, and III
Unipolar leads: aVR, aVL, aVF
Six chest (precordial) leads
Limb leads
I + III = ?
limb leads
Electrodes
Right arm
Left arm
Left leg
Right leg (ground)
Einthoven’s triangle
Lead I
= Difference in voltage between LA and RA
Lead II
= LL minus RA
Lead III
= LL minus LA
RA LA
LL
lead i
The LA electrode detects electrical voltages of the heart that are transmitted to the left arm
The RA electrode detects electrical voltages of the heart that are transmitted to the right arm
The electrocardiograph sustracts RA from LA and the difference appears as lead I.
lead i
Lead one points horizontally.
Its left pole (LA) is postive and its right pole (RA) is negative.
Therefore, lead I = LA minus RA
Lead II
Lead II points downward diagonally
Lower pole (LL) is positive and upper pole (RA) is negative.
Lead II = LL minus RA
Lead III
Lead III points downward diagonally
Lower pole (LL) is positive and upper pole (LA) is negative.
Lead III = LL minus LA
Limb leads
Add the voltage in lead I to that in lead III and you get the volatage in lead II.
I = +2
III = +5
II = +7
Augmented limb (extremity) leads
Record the electrical voltages at one location rather than relative to the voltage at another electrode
Augmented limb leads
aVR + aVL + aVF = 0
Limb leads
Frontal plane
Limb leads
Electrode and Lead are not the same thing.
chest leads
V1 to V6
unipolar
horizontal plane
Electrode placement
V1: Fourth intercostal space to the right of the sternum.
V2: Fourth intercostal space to the Left of the sternum.
V3: Directly between leads V2 and V4.
V4: Fifth intercostal space at midclavicular line.
V5: Level with V4 at left anterior axillary line.
V6: Level with V5 at left midaxillary line.
Chest leads
Frontal Plane
Horizontal Plane
Monitor leads
12 leads are not always necessary
Sample of a monitor lead
V1 (positive)
Right shoulder (negative)
Left shoulder (ground)
Holter Monitors