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+ CAPS 301: Muscle, Bodily Fluid, Cardio > Cardiac Electrophysiology > Flashcards

Cardiac Electrophysiology Flashcards

1
Q

What is excitable tissue?

A

nerves and muscle

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2
Q

How do excitable tissue communicate?

A

through AP

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3
Q

What is an action potential?

A

brief, rapid, large change in membrane potential

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4
Q

What are the 2 types of APs in heart muscle?

A
  • pacemaker cell AP

- contractile cell AP

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5
Q

What is pacemaker cell AP?

A

cells can fire AP on their own

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6
Q

What is contractile cell AP?

A

cells cannot fire AP on their own

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7
Q

What is a contractile cell?

A

ventricular myocyte

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8
Q

What is EK?

A

-90 mV

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9
Q

What is ENa?

A

+60 mV

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10
Q

What is ECa?

A

~ +60 mV, or more positive

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11
Q

What heart cells have contractile cell AP?

A

99% of heart cells

  • most cells are contractile – in ventricles especially (but atrium also has them)
  • much lower amount of conduction tissue
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12
Q

What does the stable resting membrane potential depend on?

A

K+

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13
Q

What does the sharp fast rising phase of AP depend on?

A

Na+

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14
Q

What does the plateau phase of AP depend on?

A

Ca2+ and K+

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15
Q

What is the absolute refractory period?

A

second AP can’t be fired while membrane potential is changed (during previous AP) – must wait until membrane potential returns to resting

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16
Q

What regulates the absolute refractory period?

A

Na+ state

  • Na+ channels inactivate when AP reaches peak
  • as long as Na+ cannot be fired, next AP cannot be fired
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17
Q

What is a muscle twitch?

A

muscle contraction when Ca2+ enters

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18
Q

What is tetanus?

A

sustained muscle contraction evoked when APs are emitted at very high rate

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19
Q

Compare the duration of a muscle twitch to duration of AP.

A

equal duration

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20
Q

Can twitches in skeletal muscles be summated?

A

yes

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21
Q

Can twitches in cardiac muscles be summated?

A

no – therefore, cannot tetanize heart

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22
Q

Why is tetanization of the heart bad?

A

if muscle contracted and was able to fire more APs, muscle will be constantly contracted

heart needs to beat regularly to fill and pump

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23
Q

What is the SA node?

A

(tissue) cells that can contract/fire on their own

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24
Q

Pacemaker Cell Action Potential – SA Node

A
  1. slight depolarization
    - Na+ enters slowly (first rise)
    - few different channels potentially responsible for allowing Na+ entry
  2. depolarization
    - Ca2+ enters through Ca2+ channels
    - don’t open as quickly
  3. hyperpolarization
    - K+ enters through open K+ channels
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25
Q

What are cells in the heart connected by?

A

gap junctions (ion channels)

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26
Q

What happens once AP is initiated?

A

current produced moves across heart, causing contraction of atria and then ventricles

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27
Q

What determines heart rate?

A

rate of pacemaker APs (SA node)

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28
Q

What happens to HR when slope of pacemaker potential is increased?

A

increase rate

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29
Q

What happens to HR when slope of pacemaker potential is decreased?

A

decrease rate

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30
Q

What is the primary way to increase/decrease heart rate?

A

ANS release of:

  • noradrenaline/adrenaline from SNS
  • acetylcholine from PSNS
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31
Q

What do sympathetic nerves do?

A

increase slope of pacemaker potential to speed up heart rate

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32
Q

SNS

What does noradrenaline and adrenaline do?

A

increases slope of pacemaker depolarization

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33
Q

Where is noradrenaline from?

A

nerve

34
Q

Where is adrenaline from?

A

adrenal gland

35
Q

What does PSNS do?

A

decreases slope of pacemaker potential to slow down heart rate

36
Q

PSNS

What does acetylcholine do?

A
  • decreases slope of pacemaker depolarization (takes longer to reach threshold before Ca2+ channels open and AP fires)
37
Q

PSNS

What receptors does acetylcholine act on?

A

muscarinic (M2) receptor on SA node cells

38
Q

SNS

What receptor does noradrenaline and adrenaline act on?

A

𝛽1-adrenergic receptor on SA node cells

39
Q

SNS
Noradrenaline and Adrenaline in Nodal Cells

  • receptor
  • result
A

receptor:
- 𝜷1 receptors

result:
- increase phase 4 slope
- increase heart rate

40
Q

PSNS
Acetylcholine in Nodal Cells

  • receptor
  • result
A

receptor:
- muscarinic M2 receptors

result:
- decreases phase 4 slope
- decreases heart rate

41
Q

SNS
Noradrenaline and Adrenaline in Ventricular Muscle Cells

  • receptor
  • result
A

receptor:
- 𝜷1 receptors

result:

  • increase Ca2+
  • increase stroke volume
42
Q

PSNS
Acetylcholine in Ventricular Muscle Cells

  • receptor
  • result
A

no direction action

43
Q

SNS
Noradrenaline in Vascular Smooth Muscle Cells

  • receptor
  • result
A

receptor:
- 𝛼1 receptors

result:

  • increase Ca2+
  • vasoconstriction
44
Q

SNS
Adrenaline in Vascular Smooth Muscle Cells

  • receptor
  • result
A

receptor
- 𝜷2 receptors

result:

  • decrease MLCK activity
  • vasodilation
45
Q

PSNS
Acetylcholine in Vascular Smooth Muscle Cells

  • receptor
  • result
A

limited direct action

46
Q

What is phase 4?

A

diastolic depolarization / slow depolarization / pacemaker potential

47
Q

When does phase 4 occur?

A

occurs once heart relaxes… eventually leads to next contraction

48
Q

What are the conduction tissues of the heart? (5)

A
  • SA node
  • AV node
  • bundle of His
  • left and right bundle branches
  • Purkinje fibres
49
Q

Pathway of AP

A
  1. Starts at SA node
  2. Passes through AV node
  3. Passes through Bundle of His
    - slows down when travelling here to regulate timing of contraction – allows atria to contract before ventricles
  4. Passes through left and right bundle branches (large pieces of conduction tissue)
  5. Passes through Purkinje fibres in right and left ventricles
    - moves from cell to cell via gap junctions
  6. Ventricle contracts
50
Q

How can AV node cells produce AP?

A
  • AP arrives from SA node (60-100 beats/min)

- if not, it self-depolarizes (40-50 beats/min)

51
Q

How does the AV node compare to SA node?

A

has similar properties to SA node

beats on its own

52
Q

Does AV node or SA node beat faster?

A

on their own: AV node beats slower

in the heart: both beat at same rate

53
Q

How does the SA node and AV node beat at same rate (60 bpm) in the heart?

A
  • SA node fires before AV node

- AV node becomes stimulated to fire before it would normally fire itself

54
Q

When is the only time AV node would beat on its own?

A

if something happens to SA node (ie. in disease) – would be acting as pacemaker

55
Q

What is an electrocardiogram (ECG)?

A

using recording electrodes placed on body surface to produce tangible record of electrical changes

method of measuring wave of depolarization and repolarization occurring in heart (starting from SA node)
- pattern of electrical depolarization (and repolarization) repeats itself over and over again

56
Q

What do bipolar limb leads do?

A

measure wave of depolarization

57
Q

What is Lead I?

A

right arm (-) to left arm (+)

58
Q

What is Lead II?

A

right arm (-) to left leg (+)

59
Q

What is Lead III?

A

left arm (-) to left leg (+)

60
Q

Einthoven’s Triangle

A

–

61
Q

When does ECG pen deflect upwards?

A

when depolarization moves to positive end of lead

62
Q

When does ECG pen deflect downwards?

A

when depolarization moves away from positive end of lead

63
Q

What is the P wave?

A

atrial depolarization

  • wave of atrial depolarization travels downward and left
  • as it moves down, leads pick it up as upward deflection (atrial depolarization)
64
Q

What is the QRS wave?

A

ventricular depolarization

  • more complex than atria (takes place in several stages)
65
Q

In ventricle, which cells repolarize first?

A

last cells to depolarize are first to repolarize

wave of repolarization is in opposite direction of depolarization

66
Q

What is depolarization?

A

upstroke of AP in ventricle

picked up outside of heart by leads

67
Q

What is repolarization?

A

down phase of ventricular AP

when it’s going back down to RMP

68
Q

What is the T wave?

A

ventricular repolarization

  • wave of depolarization moves away from positive end of lead
  • ECG pen deflects upward
  • produces relatively simple waveform on ECG
69
Q

What are the 2 things that have changed when repolarization begins?

A
  • direction of change in membrane voltage (depolarization → repolarization) that’s picked up from outside
  • changed direction – depolarization towards positive end = positive deflection

**if repolarization and direction changes, it’s still in upwards direction

70
Q

What is a positive deflection?

A

depolarization towards positive end

71
Q

3 Frontal Leads – Perspectives

A

–

72
Q

What is a regular (normal) heart rate?

A

60-100 beats/min

73
Q

What is paper speed?

A

25 mm/s

74
Q

What is the time that each large sqaure represents?

A

0.2 seconds

75
Q

What is the rate of normal sinus rhythm?

A

~75 beats/min [300/4 on paper]

between 60-100 beats/min

76
Q

What is the rhythm of normal sinus rhythm?

A

regular

77
Q

Are there P waves in normal sinus rhythm?

A

yes

  • all facing upwards
  • 1:1 with QRS (every QRS is preceded by P wave)
78
Q

What is sinus bradycardia?

A

elongated period between beats

79
Q

What is sinus tachycardia?

A

fast beating, not much time between beats

80
Q

What is paroxysmal atrial fibrillation?

A
  • atrial depolarization and repolarization are disorganized
  • AV node is receiving random rapid volleys of APs
  • APs proceed to ventricle depending on whether AV node is refractory or not
81
Q

What is the danger of paroxysmal atrial fibrillation?

A
  • hypotension: high irregular ventricular rate will decrease heart’s cardiac output
  • embolisms: blood flow within atria becomes stagnant and can produce clots

+ CAPS 301: Muscle, Bodily Fluid, Cardio (13 decks)

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