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Pharmacology B > Lecture 4 - Antiarrhythmics > Flashcards

Lecture 4 - Antiarrhythmics Flashcards

1
Q

In what type of patients is arrhythmia a frequent problem?

A
  • 25% of patients with digitalis (heart failure)
  • 50% of anesthetized patients
  • 80% of patients with MI
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2
Q

T or F: anti-arrhythmic drugs can produce arrhythmia

A

true

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3
Q

What is the normal pacemaker?

A

SA node

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4
Q

What are the conduction fibres??

A

AV node, bundle of His, Purkinje fibres

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5
Q

What is included in the term “healthy myocardium”?

A

atria and ventricles

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6
Q

Super briefly describe how atria and ventricles contract using SA and AV nodes

A
  • SA node causes atria to contract
  • AV node allows for a pause for ventricles to fill
  • Then ventricles contract
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7
Q

Normal cardiac rhythm = ?

A

sinus rhythm

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8
Q

Define arrhythmia

A

any rhythm that is not a normal sinus rhythm with normal AV conduction

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9
Q

What is the main pacemaker and initiator of heart beat?

A

SA node

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10
Q

SA node = ____bpm

A

60-100

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11
Q

AV node spontaneously discharges at ____ bpm (normally overridden)

A

40-60

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12
Q

What is the function of conduction fibres?

A

to excite the ventricular mass as near simultaneously as possible

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13
Q

Purkinje fibres spontaneously discharge at ___bpm (overridden)

A

20-40

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14
Q

P wave

A

atrial depolarization

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15
Q

QRS complex

A

ventricular depolarization

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16
Q

T wave

A

ventricular repolarization

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17
Q

PR interval

A

conduction time atria to ventricles

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18
Q

QRS interval

A

time for all ventricular cells to be activated

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19
Q

QT interval

A

duration of ventricular action potential

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20
Q

Most anti arrhythmic drugs act on ___ _____

A

ion channels

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21
Q

Class 1 Antiarrhythmic drugs block __ channels

A

Na

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22
Q

Class 2 Antiarrhythmic drugs block _______

A

B-receptors

**class 2 antiarrhythmics are B-blockers lol

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23
Q

Class 3 Antiarrhythmic drugs block __ channels

A

K

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24
Q

Class 4 Antiarrhythmic drugs block ___ channels

A

Ca

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25
Q

Class __ Antiarrhythmic drugs have other mechanisms

A

5

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26
Q

List some Class 1 Antiarrhythmic drugs

A

procainamide, lidocaine, flecanide

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27
Q

List some Class 2 Antiarrhythmic drugs

A

propranolol, metoprolol, esmolol (B blocker)

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28
Q

List some Class 3 Antiarrhythmic drugs

A

amiodarone, sotalol

29
Q

List some Class 4 Antiarrhythmic drugs

A

Verapamil

30
Q

List some Class 5 Antiarrhythmic drugs

A

magnesium, adenosine, digoxin

31
Q

Class 2 and 4 antiarrhythmic drugs act on _____ cells

A

pacemaking

32
Q

Class 1, 3, and 5 antiarrhythmic drugs act on _____ cells

A

non-pacemaking

33
Q

Na is higher _____

A

extracellular

34
Q

K is higher ______

A

intracellular

35
Q

Cl is higher ______

A

extracellular

36
Q

Ca is higher _____

A

extracellular

37
Q

The only ion higher intracellular is __

A

K+

38
Q

What causes depolarization?

A

positive charge in cell (Na+ and Ca2+ entering)

39
Q

What causes repolarization?

A

negative charge in cell (K+ leaving)

40
Q

What are the pacemaker cells?

A

SA node

AV node

41
Q

What are the non-pacemaker cells?

A

atria
ventricles
purkinje fibres

42
Q

Describe the electrophysiology of non-pacemaker cells:

Phase 0

A

Phase 0 - Depolarization:

  • voltage gated Na channels open
  • rapid depolarization
  • Na channels
43
Q

Describe the electrophysiology of non-pacemaker cells:

Phase 1

A

Phase 1 - Slight Repolarization:

  • Distinctive to non-pacemaker cells
  • Cl channels open briefly and chloride enters cell
44
Q

Describe the electrophysiology of non-pacemaker cells:

Phase 2

A

Phase 2 - Plateau:

  • Distinctive to non-pacemaker cells
  • Opening of Ca channels
  • Ca enters cell
  • Causes further release of Ca from SR
  • Ca dependent contraction
45
Q

Describe the electrophysiology of non-pacemaker cells:

Phase 3

A

Phase 3 - Repolarization:

  • K channels open
  • movement of K out of the cell repolarizes the membrane
  • returns to resting membrane potential
  • Ca is removed from the cytoplasm and tissue relaxes
46
Q

Describe the electrophysiology of non-pacemaker cells:

Phase 4

A

Phase 4 - Diastolic (resting) potential:

  • no time-dependent currents during phase 4
  • as a result, resting potential, is substantially more negative (-80mV) than SA/AV nodes
47
Q

Describe the electrophysiology of non-pacemaker cells:

Absolute/Relative Refractory Period

A

Phase 3:

  • Na channels recover from inactive to resting state
  • Repolarization switches sodium channels from inactive to resting
  • If the Na channels are in the inactive state the myocyte cannot be depolarized = absolute refractory period
  • If only a portion of the Na channels are in the inactive state the myocyte may depolarize but a less rapid depolarization = relative refractory period
48
Q

What does Depolarization of the resting membrane potential in non-pacemaker (fast) cells cause?

A
  • decreases the number of sodium channels available
  • decreases the rate of depolarization
  • decreases the strength and speed of the impulse

*slow depolarization of the resting membrane potential caused by hyperkalemia, schema, drugs blocking sodium channels will decrease the upstroke of eliminate it all together

49
Q

So, need completely ____ membrane and “resting” sodium channels

A

repolarized

50
Q

Describe the sodium channel gates in resting conformation

A
  • m gate closed

- h gate open

51
Q

Describe the sodium channel gates in activated conformation

A
  • m gate open

- h gate open

52
Q

Describe the sodium channel gates in inactivated conformation

A
  • m gate closed
  • h gate closed

*absolute refractory period

53
Q

How do Class 1 Antiarrhythmics alter the appearance of the action potential in non-pacemaking (fast) cells?

A

Class 1 are the Na channel blockers

  • so they would prevent the rising phase of depolarization (phase 0)
  • only affects non-pacemaking cells
54
Q

How do Class 3 Antiarrhythmics alter the appearance of the action potential in non-pacemaking (fast) cells?

A

Class 3 are K channel blockers

-so they would prevent K+ efflux and delay repolarization

55
Q

Describe the electrophysiology of pacemaker cells:

Phase 0

A
  • threshold reached - Ca channels open
  • rapid depolarization
  • then Ca channels close
56
Q

Describe the electrophysiology of pacemaker cells:

Phase 3

A

-voltage gated K channels open and membrane repolarizes

57
Q

Describe the electrophysiology of pacemaker cells:

Phase 4

A
  • spontaneous depolarization
    • pacemaker current - I f (funny current) = increased Na+ influx
    • increased Ca influx
    • decreased K efflux
  • intrinsic firing rate: SA > AV > bundle of his > purkinje fibres
  • *note: bundle of his and purkinje fibres are “fast” cells but have very slow Phase 4 depolarization
58
Q

How do Class 4 Antiarrhythmics alter the appearance of the action potential in pacemaking (slow) cells?

A

Class 4 block Ca channels

-so this would prevent Ca influx and slow the depolarization phase

59
Q

How do Class 2 Antiarrhythmics alter the appearance of the action potential in pacemaking (slow) cells?

A

Class 2 are Beta blockers

  • prevent increased Na+ influx (If)
  • prevent increased Ca2+ influx (ICa)

**don’t really understand this right now…look into it

60
Q

Non-pacemaker (fast) cells:

RMP = ?

A

-80 to -95 mV

61
Q

Non-pacemaker (fast) cells:

Phase 0 current = ?

A

sodium

62
Q

Non-pacemaker (fast) cells:

Phase 0 kinetics = ?

A

fast

63
Q

Non-pacemaker (fast) cells:

Conduction velocity = ?

A

0.5 - 5 m/sec

64
Q

Non-pacemaker (fast) cells:

Automaticity = ?

A

yes ??

65
Q

Pacemaker (slow) cells:

RMP = ?

A

-40 to -65 mV

66
Q

Pacemaker (slow) cells:

Phase 0 current = ?

A

calcium

67
Q

Pacemaker (slow) cells:

Phase 0 kinetics = ?

A

slow

68
Q

Pacemaker (slow) cells:

Conduction velocity = ?

A

0.01 to 0.1 m/sec

69
Q

Pacemaker (slow) cells:

Automaticity = ?

A

yes

Pharmacology B (21 decks)

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