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48 Cards in this Set
- Front
- Back
How do cellular electro-physiologists measure potentials of a cell?
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by measuring the INSIDE of the cell with respect to the OUTSIDE
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How do electrocardiographers measure potentials of a cell?
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the electrodes "see" the potential on the OUTSIDE of the cell; measurements are recorded as the potential difference between 2 electrodes
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What is an isoelectric potential? When does this occur?
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A flat line recorded, when there is no potential difference between 2 electrodes; occurs when region is depolarized or fully repolarized
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when is an upward deflection recorded?
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when depolarization heads toward the positive electrode
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when is a downward deflection recorded?
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when a depolarizing wave moves away from the positive electrode
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What is occurring during the PQ Segment?
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Atria contract
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What happens during the ST segment?
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Ventricles contract
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What can lead to long QT?
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cardiac ion channelopathies: gain-of-function for Na or loss of function K+ channels can result in prolonged QT interval
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diagram how electrical depolarization of the ventricle proceeds
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from septum, toward apex, back up the walls, then the base
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Where are leads V1 and V2 located?
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over the right heart
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Where are leads V5 and V6 located?
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over the left side of the heart
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Where are the V3 and V4 leads located
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over the interventricular septum; they are transitional leads
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How can HR be determined from the ECG?
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by the R-R interval (aka the number of "large boxes" [aka 5 small boxes]) of .2 seconds
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1 large box equals what heart rate?
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300 beats/min
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2 large boxes equals what heart rate?
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150
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3 large boxes equals what heart rate?
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100
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4 large boxes equals what heart rate?
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75
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5 large boxes equals what heart rate?
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60
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6 large boxes equals what heart rate?
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50
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How are the electrodes arranged in AVR?
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Right arm is positive; left arm/leg act as negative
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How are the electrodes arranged in AVL?
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left arm is positive electrode; right arm/left leg are negative
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How are the electrodes arranged in AVF?
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foot is positive electrode; left and right arms act as negative
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What do V1-V6 measure for an EKG?
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measure electrical depolarization in the horizontal plan
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Why is repolarization causing an upstroke (aka going in the same direction as the depolarization on the EKG)
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as repolarization occurs, the positive electrode will start to see a positive charge building up outside the cell because that portion is becoming negative inside the cell first. (remember the whole repolarization occurring in the opposite direction as depolarization)
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for lead III, what will the EKG look like
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atrial: up
ventricular: up repolarization: up |
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for lead II, what will the EKG look like
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atrial: up
ventricular: up repolarization: up |
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For lead I what direction will the drawing be for atrial, ventricular and repolarization
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atrial: up
ventricular: up repolarization: up |
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in Einthoven’s triangle what is the configuration of positive and negative leads
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I: left arm positive, right arm negative
II: right arm negative, left leg positive III: left arm negative, left leg positive |
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What are the bipolar leads?
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I, II, III
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if conduction is slowed through the bundle of his, or purkinje fibers, what happens to the PR interval?
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you will not see prolongation of PR interval, but a widening of the QRS
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if conduction is slowed through the AV node, what happens to the PR interval?
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it becomes prolonged
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What is assumed to be the zero baseline?
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the T-P segment
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What is the U wave?
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repolarization of myocardial m cells
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What is the T-P segment
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end of one cycle to the beginning of the other cycle; assumed to be zero baseline
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What is clinically important about the Q-T interval
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see arrhythmia there often, since it covers all of systole
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Q-T interval
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duration of ventricular systole (includes depolarization of ventricle, plus repolarization of ventricle; starts at QRS and ends at T)
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S-T interval
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all of repolarization of the ventricles
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T- wave
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rapid ventricular repolarization
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What is occurring during the S-T segment tell you?
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ventricle is fully depolarized, represents plateau phase (this is isoelectric because the electrodes aren't seeing a difference btw. one another)
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What does the QRS interval tell you on an ECG?
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activation of the ventricles, all about ventricular depolarization
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What does the P wave show us on an ECG
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atrial depolarization
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What does the P-R interval tell you on an ECG?
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P wave plus P-R segment
conduction through the atria and the AV node |
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What is seen in the P-R segment of an ECG
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AV node
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what can the horizontal portion of an ECG tell you?
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1) time btw events
2) breadth of the wave (how long it takes depol/repol to spread; size and/or speed of conduction) |
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what can the magnitude of the deflection tell you on an ECG
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the amplitude of the wave
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What is an interval on an ECG
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it includes AT LEAST one wave
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On an ECG, how many seconds are the equivalent of 5mm (or 5 boxes)
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0.2 seconds
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How does repolarization occur in the heart, in what order?
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The last to depolarize is the first to repolarize (remember order of depolarization is endo to epi, apex to base)
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