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48 Cards in this Set

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