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What is an electric dipole?
Charge separation (pos and neg)
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How do dipoles generated by the heart produce the waves on ECG?
- Depolarizing current that begins near negative electrode creates an upward deflection
- Repolarizing current that begins near positive electrode creates a downward deflection
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If you have a negative electrode where the depolarization begins, what kind of deflection will you get on ECG?
Upward
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If you have a positive electrode where the depolarization begins, what kind of deflection will you get on ECG?
Downward
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What is the placement of the negative and positive electrodes for lead I?
- Negative electrode on right arm
- Positive electrode on left arm
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What is the placement of the negative and positive electrodes for lead II?
- Negative electrode on right arm
- Positive electrode on left leg
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What is the placement of the negative and positive electrodes for lead III?
- Negative electrode on left arm
- Positive electrode on left leg
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What is the mean electrical vector?
The average of all the individual wave fronts (average direction of the wave)
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ECG uses 6 limb leads, some are unipolar and some bipolar. Which ones?
- Leads I, II, III are bipolar
- aVF, aVL, aVR are unipolar
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What is Einthenhoven’s Law?
Lead I potential + lead III potential = lead II potential
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The magnitude of deflection is greatest when the mean vector of the current is ___________________ to the lead
Parallel
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What does P wave represent?
Atrial depolarization
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What does QRS complex represent?
Ventricular depolarization
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What does T wave represent?
Ventricular repolarization
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What does PR interval represent?
Time between atrial and ventricular depolarization
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What does QT interval represent?
Time between start of ventricular depolarization and end of ventricular repolarization
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What does ST segment represent?
Time between end of ventricular depolarization and beginning of ventricular repolarization
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In what direction is the depolarization traveling in the heart during Q wave?
From left ventricle to right, slight upwards left axis
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In what direction is the depolarization traveling in the heart during R wave?
Down towards apex, parallel to lead II
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In what direction is the depolarization traveling in the heart during S wave?
Upwards toward lead I
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The unipolar limb leads are all positive/negative, meaning any depolarization traveling toward the electrode will show a upward/downward wave
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What is the normal mean electrical vector (axis) for ventricular depolarization?
-30 to 90 degrees
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