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