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CCRN > C2: Cardiovascular: Conduction System > Flashcards

C2: Cardiovascular: Conduction System Flashcards

0
Q

List three types of cardiac cells

A
  1. Pacemaker cells
  2. Electrical conducting cells
  3. Myocardial muscle cells
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1
Q

List the properties of cardiac cells

A
  1. Automaticity
  2. Excitability
  3. Conductivity
  4. Contractility
  5. Rhythmicity
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2
Q

Define automaticity

A

The ability of certain cardiac cells to initiate impulses regularly and spontaneously

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3
Q

Define excitability

A

The ability of cardiac cells to respond to stimulus

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4
Q

Define conductivity

A

The ability of cardiac cells to transmit impulses

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5
Q

Define contractility

A

The ability of cardiac cells to respond to an impulse with muscle contraction

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6
Q

Define rhythmicity

A

The ability of cardiac cells to generate an action potential at a regular rate

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7
Q

What section of EKG does Phase 4 correspond to?

A

the isoelectric line btwn T wave and QRS

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8
Q

What are the phases of the AP of myocardial cells?

A
  • Phase 4: Resting membrane potential
  • Phase 0: Rapid depolarization of the cell
  • Phase 1: Brief, partial repolarization
  • Phase 2: slowing of repolarization causing plateau
  • Phase 3: Sudden acceleration in rate of repolarization
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9
Q

What is the electrical charge within a cell?

A

-80 to -95 mV

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10
Q

Is the interior of a cell more negative or positive?

A

negative

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11
Q

How is negativity (and therefore resting membrane potential) maintained within a cell?

A

sodium potassium pump

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12
Q

Describe the ionic movement done by the Na-K pump

A

K pumped into cell

Na pumped out of cell

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13
Q

How does shock impact the resting membrane potential?

A

low supplies of ATP (energy) cannot maintain the Na-K pump .:. irritability occurs

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14
Q

Which part of the EKG coincides with phase 0?

A

QRS: rapid depolarization

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15
Q

When a stimulus is applied to the cell, cell membrane permeability INCREASES. How does this impact ionic movement during phase 0?

A

Na rushes into the cell (influx)

K begins to move out of the cell (efflux)

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16
Q

What is the threshold potential?

A

-60 to -70 mV

when the cell responds entirely and depolarization occurs

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17
Q

Phase 0 is defined by what ionic movement?

A

sodium (fast) channel

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18
Q

Which meds BLOCK depolarization and achievement of threshold potential?

A

Class I Antidysrhythmics

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19
Q

How do class I Antidysrhythmics act?

A

they block the influx of sodium into the cell .:. preventing threshold potential and depolarization

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20
Q

Examples of Class I Antidysrhythmics?

A
  1. procainamide
  2. quinidine
  3. lidocaine
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21
Q

Describe the ionic movement in Phase 1.

A

*brief, partial repolarization

Na channels close

K efflux continues

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22
Q

What part of the EKG does Phase 2 coincide with?

A

ST segment

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23
Q

Describe ionic movement during phase 2.

A

CALCIUM INFLUX keeps cell isoelectric but still depolarized as K efflux occurs at approximately the same rate

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24
Q

What is the significance of the plateau during phase 2?

A

allows for a sustained contraction

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25
Q

Phase 2 is defined by what ionic movement?

A

CALCIUM (SLOW) CHANNELS

26
Q

Which drugs are Rx for to impact phase 2?

A

Class IV antidysrhythmics (Ca channel blockers)

27
Q

MOA of Class IV antidysrhythmics (Ca channel blockers)?

A

block the movement of Ca and prolong repolarization and refractoriness

28
Q

Examples of Class IV Antidysrhythmics (Ca channel blockers)?

A
  1. verapamil

2. diltiazem

29
Q

Describe the ionic movement in Phase 3

A

K movement ACCELERATES in this phase

K efflux occurs at the beginning of phase 3 to exceed the influx of Ca

K influx occurs at the end of phase 3

30
Q

Which drugs target Phase 3?

A

Class III Antidysrhythmics

31
Q

MOA of Class III Antidysrhythmics

A

Block the movement of K during this phase (prolongs refractoriness)

32
Q

Examples of Class III Antidysrhythmics

A
  1. amiodarone
  2. ibutilide
  3. dofetilide
33
Q

What is phase 4?

A

resting membrane potential

34
Q

What is a unique property of pacemaker cells?

A

automaticity

35
Q

Describe the depolarization process of pacemaker cells

A

Slow diastolic depolarization d/t a time-dependent leak of Na into the cell. When enough Na has entered the cell, the threshold potential is reached, and SPONTANEOUS depolarization occurs

36
Q

What does the rate of diastolic depolarization determine?

A

the intrinsic rate of pacemakers

37
Q

PM cells and their rates?

A
  1. SA node: 60-100 BPM
  2. AV jxn: 40-60 BPM
  3. Purkinje fibers: 20-40 BPM
38
Q

When does the absolute refractory period occur?

A

Phase 0 through midphase 3 aka from the QRS complex to the peak of the T wave

39
Q

What can an R-on-T lead to?

A

Vtach or Vfib

40
Q

If the impact is strong enough, at which point can the cell abnormally respond?

A

relative refractory period

41
Q

When does the relative refractory period occur?

A

late phase 3 of the AP aka the descending limb on the T wave

42
Q

What is the effective refractory period?

A

absolute + relative refractory period

43
Q

What is the function of the SA node?

A

the natural PM of the heart because it has the fastest intrinsic rate (60-100 bpm)

44
Q

List the 3 internodal pathways btwn the SA node and the AV node

A
  1. Anterior tract (Bachmann’s)
  2. Middle tract (Wenckebach’s)
  3. Posterior tract (Thorel’s)
45
Q

Describe the pathway of Bachmann’s bundle

A

the INTERATRIAL pathway: from RA to LA

46
Q

Does the AV node contain PM cells?

A

no–primary fxn is to SLOW the impulse down

47
Q

What physiologic impact does the AV node have?

A

Accounts for the 0.08-0.12 s delay, which allows the atria to depolarize completely, contract, and finish filling the ventricles BEFORE the ventricles are stimulated

48
Q

Define AV junction

A

the tissue that surrounds the AV node and bundle of His that contains PM cells

49
Q

AV junction fxn?

A

A secondary pacemaker w/ intrinsic rate of 40-60 bpm

50
Q

In the intraventricular conduction system, the bundle of His branches into what?

A
  1. RBB

2. LBB

51
Q

Which BB divides into 3 hemibundles?

A

LBB

52
Q

What are the 3 hemibundles a/w the LBB and what do they depolarize?

A
  1. Septal hemibundle: depolarizes IVS in L to R direction
  2. Left anterior hemibundle (LAH): depolarizes the anterior and superior LV
  3. L posterior hemibundle (LPH): depolarizes the posterior and inferior LV
53
Q

Which hemibundle is most susceptible to block?

A

the anterior hemibundle

54
Q

Why is the posterior hemibundle less susceptible to block?

A

thicker & has a dual blood supply

55
Q

What is the clinical outcome of block at the septal hemibundle?

A

not significant

56
Q

What are the fascicles?

A
  1. RBB
  2. LAH
  3. LPH

*unifasicular, bifasicular, and trifasiclular block

57
Q

What do the fascicles further divide into?

A

Purkinje fibers

58
Q

Where do the Purkinje fibers carry the impulses

A

Through the ventricular walls

59
Q

What is an important fxn of the Purkinje fibers?

A

Acts as final pacemaker if upper pacemakers fail

60
Q

What is the functional syncytium?

A

capability of mycardium to respond as if it were one muscle d/t intercalated discs

61
Q

Direction of depolarization of cardiac chambers?

A

from endocardium to epicardium

62
Q

Direction of repolarization of cardiac chambers?

A

from epicardium to endocardium

CCRN (2 decks)

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