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38 Cards in this Set

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What does the EKG tell us about?
The electrical and mechanical events that are occuring in the heart.
On the electrocardiogram, what does the P wave represent?
Depolarization of the atria
On the electrocardiogram, what does the QRS wave represent?
Depolarization of the ventricles
What does the deviation of the QRS wave show?
The magnitude of the depolarization of the ventricles
What does the interval between the P wave and the QRS wave represent?
The time that it takes for depolarization to move from the atria across the AV node to the ventricles.
What does the T wave represent?
The repolarization of the ventricles
Where is the atrial repolarization on the EKG?
Buried in the QRS wave - it is masked.
What is the RR interval an indication of?
Heartrate
What does the deviation of the EKG waves indicate?
The voltage across the heart
What does the voltage across the heart depend upon when measuring an EKG?
The placement of the electrodes
What is not changed by the placement of electrodes?
The Timing of events
What does an EKG measure?
The flow of current through the heart - both its magnitude and its direction.
As a cell becomes depolarized, what does the charge of its surface become?
Negative
In what direction does the spread of depolarization move as the heart depolarizes?
From the base to the apex
What is Einthoven's Triangle?
The conventional arrangement of electrodes for recording standard ECG leads
Where are the electrodes placed for Lead 1?
Neg = right arm
Pos = Left arm
Where are the electrodes placed for lead 2?
Neg = right arm
Pos = left leg
Where are the electrodes placed for lead 3?
Neg = Left arm
Pos = Left leg
What is Einthoven's law?
The rule that if you know 2 of the 3 leads at any given instant the third can be determined by summing the first two.
How do you calculate the voltage across a lead?
Positive - Negative
Because we measure the conduction paths of the heart, what does that allow us to use?
Vectors
When using Vectors to represent electrical potentials, what does the LENGTH represent?
The magnitude of the voltage
When using Vectors to represent electrical potentials, in what direction does the arrowhead point??
Positive
Why do we represent the heart's electrical activity with vectors?
Because it gives us a multi-dimensional look at the activities in the heart.
When is there a mean vector through the ventricles?
When they are partially depolarized
What is the vector when the ventricle is completely depolarized?
Zero
What is the NORMAL mean vector in the heart?
+59
What are the quadrants of the heart vectors?
Opposite what's normal
Go clockwise from the right x axis in a circle.
Why does the repolarization of the ventricles indicated by the T wave make another positive deflection instead of a dip on the EKG?
Because Repolarization occurs in the OPPOSITE direction to DEPOLARIZATION and since this is now pos charge replacing negative, it ends up the same.
Do the atria repolarize in the same manner as the T wave?
No, actually they repolarize in the same direction as they depolarize.
So how does the repolarization wave for the atria compare to that for the depolarization of it?
It is a negative deflection
Why don't you see the repolarization wave of the atria?
Because it's buried in the QRS wave.
When you have left heart hypertrophy what direction does the mean axis of the heart point?
Toward the left
What quadrant is the mean axis in when there is left heart hypertrophy?
To the upper right quadrant - left axis deviation
Why does the mean axis point toward the side of hypertrophy?
Because there is more muscle mass, so more positive charge as the wave of depolarization spreads across the heart.
Does the left axis deviation occur only because of increased muscle mass?
No; it is also due to the increased time that it takes for the depolarization to spread across all that mass.
What direction do the vectors point in when you project them onto their leads for the EKG?
Always in the positive direction
So where does the axis of deviation usually point?
in the direction of the abnormality in the heart.