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Physiology Exam 2 > 15 and 16 - Electrocardiogram I and II > Flashcards

15 and 16 - Electrocardiogram I and II Flashcards

1
Q

While you are rounding in outpatient IM, a patient taking a beta blocker for high blood pressure is seen. Noting his slow heart rate, you know the mechanism of this effect is:

a, Increasing the rate of decline of K+ permeability during phase 4 of SA nodal cells.

b. Having a positive inotropic effect on myocardial cells.
c. Increasing the slope of the SA nodal cell (“pacemaker”) prepotential.
d. Decreasing the rate of influx of sodium and calcium during phase 4 of SA nodal cells.

A

d. Decreasing the rate of influx of sodium and calcium during phase 4 of SA nodal cells.

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2
Q

Fast sodium channel blockers would be expected to have the LEAST effect on which cells:

a. SA nodal cells
b. Atrial myocytes
c. Ventricular myocytes
d. Purkinje fiber cells

A

a. SA nodal cells

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3
Q

What is an ECG?

A

A body surface recording of a change in electrical potential which is a projection of the net potential changes occurring in the heart

The summation of all the depolarization and repolarization currents occurring in cardiac tissue

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4
Q

Describe the horizontal axis of ECG chart paper

A
  • It is divided into 1 mm sections

- One small square is equal to 1/24 of a second, or 0.04 seconds

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5
Q

Describe the vertical axis of ECG chart paper

A
  • A 10 mm deflection is equal to 1 mV

- At rest, the line will be at the vertical midpoint of the paper

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6
Q

How many small vertical lines will pass under the pen of an ECG machine in 2 second?

A

24

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7
Q

A 10 mm vertical deflection represents ____ mV

A

1

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8
Q

What is an isoelectric line?

A

The vertical midpoint of the ECG paper (0 mV)

  • If it goes up, it is a positive deflection
  • If it goes down, it is a negative deflection
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9
Q

What is a P-wave?

A

It represents atrial depolarization (sum of all phase 0’s in the atrial tissues)

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10
Q

What is the P-R interval?

A

The amount of time from the beginning of the P wave (beginning of atrial depolarization) to the beginning of the QRS complex (the beginning of ventricular depolarization)

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11
Q

What is the normal duration of the P-R interval?

A

0.12 to 0.20 seconds

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12
Q

What does a shorter than normal duration of the P-R interval suggest?

A

The existence of a bundle of Kent, which is an embryological pathway around the AV node that should no exist

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13
Q

What is a first degree block?

A

Conduction through the AV node is reduced, and the PR interval is excessively long, but all P waves still result in a QRS

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14
Q

What is a second degree block?

A

Not all P waves will result in a QRS complex because some did not go all the way through the AV node

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15
Q

What is a third degree block?

A

There are NO P waves conducted though the AV node because there is a complete block

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16
Q

What is the P-R segment?

A

When the recording returns to baseline after the P-wave

Depolarization is now slowly going through the AV node

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17
Q

What is the QRS complex?

A

A sequential depolarization of the ventricular cells (sum of all phase 0’s in the ventricular cells)

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18
Q

What is the duration of the QRS complex?

A

About 0.08 seconds

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19
Q

What happens if the QRS complex is over 120 ms (0.12 seconds)

A

There is a block in the right or left bundle

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20
Q

What is the Q-wave of the QRS complex?

A

Any negative deflection that precedes the R wave

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21
Q

What is the R-wave of the QRS complex?

A

Any positive deflection in the QRS complex

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22
Q

What is the S-wave of the QRS complex?

A

Any negative deflection that follows the R-wave

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23
Q

What is the S-T segment?

A

It represents the long time period through phase 2 (non-polar plateau)

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24
Q

What happens to the S-T segment with any acute injury?

A

Phase 2 will occur at some voltage (positive or negative) other than zero

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25
Q

What accounts for this voltage difference?

A

It is due to the lack of current flow between the normal areas and the abnormal areas of the myocardium

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26
Q

What is the T wave?

A

The ventricular re-polarization (summation of all phase 3’s in ventricular cells)

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27
Q

What is the U wave?

A

It may represent re-polarization of the papillary muscles or the purkinje conduction system

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28
Q

What represents all the phase 0’s of atrial muscle cells on an ECG?

A

The P wave

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29
Q

What represents all the phase 0’s of ventricular muscle cells on an ECG?

A

The QRS complex

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30
Q

What represents all the phase 3’s in ventricular muscle cells on an ECG?

A

The T wave

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31
Q

What is a normal duration of the P-R interval?

A

About 140 ms or 0.14 seconds

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32
Q

What is a normal duration of the QRS complex?

A

80-120 ms or 0.08 to 0.12 seconds

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33
Q

What are the three unipolar limb leads?

A
  • AVR
  • AVL
  • AVF
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34
Q

What do the unipolar limb leads do?

A

They allow us to compare voltage differentials between a single point on the body and a grounded reference point

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35
Q

Give an example of how the unipolar limb leads work, using AVR as an example

A
  • Place a positive lead on the right arm (AVR) and a negative lead on the left arm (AVL) and left leg (AVF)
  • The right lead (AVR) will then BISECT the angle created by the intersection of leads I and II… It will be perpendicular to lead III
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36
Q

Is it the same for AVF and AVL?

A

Yes…

When AVF is the positive lead, it will bisect lead II and III

When AVL is the positive lead, it will bisect lead I and III

37
Q

What are the three sets of bipolar limb leads?

A
  • Lead I: LA (+) and RA (-)
  • Lead II: RA (-) and LL (+)
  • Lead III LA (-) and LL (+)
38
Q

What do bipolar limb leads do?

A

They measure the potential differences between two points on the ody

39
Q

What do the three bipolar limb leads form?

A

They form an equilateral triangle called Einthoven’s triangle

40
Q

What plane do all of these leads measure?

A

These all measure ECG in the frontal plane

41
Q

How may unipolar chest leads are there?

A

Six

42
Q

What are the names of the unipolar chest leads?

A 
V1
V2
V3
V4
V5
V6
43
Q

Where do we place V1?

A

At the 4th intercostal space on the right sternal border

44
Q

Where do we place V2?

A

At the 4th intercostal space on the left sternal border

45
Q

Where do we place V3?

A

Midway between V2 and V4 on the line joining the two points

46
Q

Where do we place V4?

A

At the 5th intercostal space, midclavicular line on the left side

47
Q

Where do we place V5?

A

At the anterior axillary line at the same level as V4

48
Q

Where do we place V6?

A

At the midaxillary line at the same level as V4 and V5

49
Q

What is the purpose of the unipolar chest leads?

A

They allow us to analyze ECGs in the horizontal plane

50
Q

How can you predict if the P-wave and QRS complex will be positive or negative in the limb leads?

A

You can look at the average vector of ATRIAL depolarization and the average vector for VENTRICULAR depolarization

51
Q

Describe the process of predicting the direction of the P-wave and QRS complex

A
  • Look a the direction that the vector points
  • If it points towards the positive pole, the deflection of the P-wave and QRS complex will be positive (and vice versa for negative)
  • If the vector is parallel to the lead, the resultant vector will be large
52
Q

There are three ways to determine the heart rate from an ECG. What are they?

A

1 - Formula
3 - Division by 300
4 - Marked paper

53
Q

What is the formula method of determining the heart rate from an ECG?

A
  • Select two points of consecutive R waves
  • Count the number of large boxes (this is n)

Heart rate = 1/n x chart speed

54
Q

What is the division by 300 method of determining the heart rate from an ECG?

A
  • Memorize the numbers… 300, 150, 100, 75, 60, 50
  • Each number corresponds to the number of large boxes between R waves
  • If there is just one box between the waves, it is 300 bpm
  • If there are four boxes between them, it is 75 bpm
55
Q

What is the marked paper method of determining the heart rate from an ECG?

A
  • Most hospitals use paper marked at three second intervals

- Count the QRS complexes in a 6 second interval and multiply by 10

56
Q

What would a normal sinus rhythm look like (bpm)?

A

The resting heart rate would be between 60-100 bpm

57
Q

What is tachycardia?

A

When the resting heart rate is greater than 100 bpm

58
Q

What is bradycardia?

A

When the resting heart rate is lower than 60 bpm

59
Q

What is the hexaxial reference system in the frontal plane?

A
  • It is a tool that utilizes the equilateral triangle formed by leads I, II and III and the unipolar chest leads
  • The center point of this reference tool is the AV node
  • The axis of each lead is moved so that it intersects with the AV node at its midpoint
60
Q

What degrees of the circle will you find each of the leads included?

A
  • AVF: +90 (bottom of circle)
  • Lead I: +180 (left of circle)
  • AVR: -150 (left upper)
  • Lead II: -120 (left upper)
  • Lead III: -60 (right upper)
  • AVL: -30 (right upper)
61
Q

What is meant by a “normal axis”?

A

The vector lies between 0 and 90 degrees (bottom right)

62
Q

What is meant by “right axis deviation”?

A

The vector lies between 90 and 180 degrees (bottom left)

63
Q

What is meant by “left axis deviation”?

A

The vector lies between 0 and -90 degrees (top right)

64
Q

There are four steps in the process of determining the approximate mean electrical axis in the frontal plane. What is the first step?

A

First, you need to select any two leads that are 90 degrees apart from each other

Example: Lead I and AVF are convenient because they are horizontal and vertical, respectively

65
Q

What do you do after you have selected two leads that are 90 degrees apart from each other?

A

For this example (Lead I and AVF), you would evaluate the QRS in lead I

If the QRS in lead I is deflected in the positive direction, the vector will point to the left because that is the positive pole

66
Q

After you have ealuated the QRS in lead I, what do you do?

A

Evaluate the QRS in AVF

If the QRS in AVF is deflected in the positive direction, the vector will point down because that is the positive pole

67
Q

What do you do after you have determined the direction of both vectors?

A

Use vector addition to determine the resultant mean axis

68
Q

What is a possible pathological reason that the PR interval would be shorter than normal?

A

A first degree block in the conduction through the AV node

69
Q

What is a possible pathological reason that the PR interval would be shorter than normal?

A

It can be a normal, harmless variant, but it can also indicate…

  • Wolff–Parkinson–White syndrome
  • Lown–Ganong–Levine syndrome
70
Q

What is a possible pathological reason that you would see a very large and wide QRS complex appearing in a lead with mostly normal QRS complexes?

A

Uhhh… Ask Leslie?

71
Q

What is a possible pathological reason that the QRS complex would consistently appear large and wide?

A

1 - A bundle branch block (conduction block)

2 - Hyperkalemia

72
Q

What happens to the heart rate in the case of increased sympathetic tone?

A

Increased heart rate

fight or flight = fast HR

73
Q

What happens to the heart rate in the case of increased activation of beta-one receptors on the SA node?

A

Increase heart rate in SA node

chronotropic effect

74
Q

What happens to the heart rate in the case of decreased sympathetic tone?

A

Decreased heart rate

75
Q

What happens to the heart rate in the case of decreased activation of beta-1 receptors on the SA node

A

Decrease heart rate in the SA node

works against the chronotropic effect

76
Q

What happens to the heart rate in the case of increased vagal tone

A

Decreased heart rate

Vagus works with parasympathetics

77
Q

What happens to the heart rate in the case of increased activation of muscarinic receptors on the SA node?

A

Decreased heart rate (M2 receptors)

opposite for M3 receptors

78
Q

What happens to the heart rate in the case of decreased vegal tone?

A

Increased heart rate

Less parasympathetics at work

79
Q

What happens to the heart rate in the case of decreased activation of muscarinic receptors on the SA node?

A

Increased heart rate (M2 receptors)

opposite for M3 receptors

80
Q

What happens to the conduction velocity through the AV node in the case of increased sympathetic tone?

A

Conduction velocity increases

81
Q

What happens to the conduction velocity through the AV node in the case of increased activation of beta-1 receptors on the SA node?

A

Conduction velocity increases

82
Q

What happens to the conduction velocity through the AV node in the case of decreased sympathetic tone?

A

Conduction velocity decreases

83
Q

What happens to the conduction velocity through the AV node in the case of decreased activation of beta-1 receptors on the SA node?

A

Conduction velocity decreases

84
Q

What happens to the conduction velocity through the AV node in the case of increased vagal tone?

A

Decreased conduction velocity (could even lead to a conduction block)

85
Q

What happens to the conduction velocity through the AV node in the case of increased activation of muscarinic receptors on the SA node?

A

Reduced conduction velocity

86
Q

What happens to the conduction velocity through the AV node in the case of decreased vagal tone?

A

Increased conduction velocity

87
Q

What happens to the conduction velocity through the AV node in the case of decreased activation of muscarinic receptors on the SA node?

A

Increased conduction velocity

88
Q

What is the definition of an agonist and an antagonist?

A

Agonist: a chemical that binds to a receptor and activates the receptor to produce a biological response

Antagonist: a substance that interferes with or inhibits the physiological action of another

Physiology Exam 2 (11 decks)

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