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CCRN > C2: Cardiovascular: Conduction System > Flashcards

C2: Cardiovascular: Conduction System Flashcards

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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
What is the significance of the plateau during phase 2?
allows for a sustained contraction
25
Phase 2 is defined by what ionic movement?
CALCIUM (SLOW) CHANNELS
26
Which drugs are Rx for to impact phase 2?
Class IV antidysrhythmics (Ca channel blockers)
27
MOA of Class IV antidysrhythmics (Ca channel blockers)?
block the movement of Ca and prolong repolarization and refractoriness
28
Examples of Class IV Antidysrhythmics (Ca channel blockers)?
1. verapamil | 2. diltiazem
29
Describe the ionic movement in Phase 3
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
Which drugs target Phase 3?
Class III Antidysrhythmics
31
MOA of Class III Antidysrhythmics
Block the movement of K during this phase (prolongs refractoriness)
32
Examples of Class III Antidysrhythmics
1. amiodarone 2. ibutilide 3. dofetilide
33
What is phase 4?
resting membrane potential
34
What is a unique property of pacemaker cells?
automaticity
35
Describe the depolarization process of pacemaker cells
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
What does the rate of diastolic depolarization determine?
the intrinsic rate of pacemakers
37
PM cells and their rates?
1. SA node: 60-100 BPM 2. AV jxn: 40-60 BPM 3. Purkinje fibers: 20-40 BPM
38
When does the absolute refractory period occur?
Phase 0 through midphase 3 aka from the QRS complex to the peak of the T wave
39
What can an R-on-T lead to?
Vtach or Vfib
40
If the impact is strong enough, at which point can the cell abnormally respond?
relative refractory period
41
When does the relative refractory period occur?
late phase 3 of the AP aka the descending limb on the T wave
42
What is the effective refractory period?
absolute + relative refractory period
43
What is the function of the SA node?
the natural PM of the heart because it has the fastest intrinsic rate (60-100 bpm)
44
List the 3 internodal pathways btwn the SA node and the AV node
1. Anterior tract (Bachmann's) 2. Middle tract (Wenckebach's) 3. Posterior tract (Thorel's)
45
Describe the pathway of Bachmann's bundle
the INTERATRIAL pathway: from RA to LA
46
Does the AV node contain PM cells?
no--primary fxn is to SLOW the impulse down
47
What physiologic impact does the AV node have?
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
Define AV junction
the tissue that surrounds the AV node and bundle of His that contains PM cells
49
AV junction fxn?
A secondary pacemaker w/ intrinsic rate of 40-60 bpm
50
In the intraventricular conduction system, the bundle of His branches into what?
1. RBB | 2. LBB
51
Which BB divides into 3 hemibundles?
LBB
52
What are the 3 hemibundles a/w the LBB and what do they depolarize?
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
Which hemibundle is most susceptible to block?
the anterior hemibundle
54
Why is the posterior hemibundle less susceptible to block?
thicker & has a dual blood supply
55
What is the clinical outcome of block at the septal hemibundle?
not significant
56
What are the fascicles?
1. RBB 2. LAH 3. LPH *unifasicular, bifasicular, and trifasiclular block
57
What do the fascicles further divide into?
Purkinje fibers
58
Where do the Purkinje fibers carry the impulses
Through the ventricular walls
59
What is an important fxn of the Purkinje fibers?
Acts as final pacemaker if upper pacemakers fail
60
What is the functional syncytium?
capability of mycardium to respond as if it were one muscle d/t intercalated discs
61
Direction of depolarization of cardiac chambers?
from endocardium to epicardium
62
Direction of repolarization of cardiac chambers?
from epicardium to endocardium

CCRN (2 decks)

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