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Drug Action I > Block 3 - Conduction and Rhythm > Flashcards

Block 3 - Conduction and Rhythm Flashcards

1
Q

What is intrinsic control?

A

Heart depolarizes and contracts w/o NS stimulation

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2
Q

What is extrinsic control

A

Rhythm can be altered by ANS

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3
Q

What factors coordinate heart beat?

A
  1. Gap junctions
  2. Intrinsic cardiac conduction system
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4
Q

What are the components of intrinsic cardiac conduction system?

A
  1. Network of non contractile (auto rhythmic cells)
  2. Initiate and distribute impulses → coordinated depolarization and contraction of heart
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5
Q

Describe the activity of pacemaker cells (action potential)?

A
  1. Pacemaker potential: Repolarization closes K+ channels and opens slow Na+ channels → ion imbalance →
  2. Depolarization:
    Ca2+ channels open → huge influx → rising phase of action potential
  3. Repolarization
    K+ channels open → efflux of K+
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6
Q

Unstable resting membrane potential is caused by?

A

Opening of slow Na+ channels

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7
Q

At threshold, ___ channels open?

A

Ca2+

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8
Q

Explosive Ca2+ influx produces ___

A

Rising phase of action potential

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9
Q

Describe the action potential initiation by contractile cardiomyocytes?

A
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10
Q

Describe the sequence of excitation?

A

SA node → Av node → V bundles → right and left bundle branches → Purkinje fibers (subendocardial conducting network)

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11
Q

What is the purpose of the SA node?

A
  1. Pacemaker of heart in right atrial wall
  2. Depolarizes faster than the rest of the heart
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12
Q

SA node impulse? Inherent rate?

A

75x/min (sinus rhythm)

100X/min

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13
Q

How does AV node differ from SA?

A
  1. Delays impulse 0.1 sec
  2. Smaller fibers → fewer gap junctions
  3. Atrial contraction
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14
Q

Inherent rate of AV nodes?

A

50x/min without SA node input

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15
Q

What is the function of AV bundles?

A

Only electrical connection between atria and ventricles

(not connected by gap junctions)

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16
Q

What is the function of the right and left bundle branches?

A

Carry impulses toward apex of heart

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17
Q

What is the function of subendocardial conducting network?

A
  1. Complete pathway through inter ventricular septum into apex and ventricular wall
  2. More elaborate on left side of heart
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18
Q

Intrinsic rate of Punjenke fibers?

A

Depolarizes 30X/min in absence of AV node input

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19
Q

What happens after Pujenke fibers?

A

Ventricular contraction from apex toward atria

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20
Q

Describe the overal intrinsic cardiac conduction system during action potential?

A
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21
Q

Identify the action potential shapes?

A
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22
Q

What occurs during extrinsic innervation of the heart?

A

ANS via cardiac centers in medulla oblongata
1. Sympathetic → Increased rate and force
2. Parasympathetic → Decrease rate
3. Cardioacceleratory center → stimulate SA, AV, muscles, and coronary arteries
4. Cardioinhibitory center → inhibits SA and AV via vague nerves

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23
Q

What are the components of ECG?

A
  1. P wave – depolarization SA node → atria
  2. QRS complex - ventricular depolarization and atrial repolarization
  3. T wave - ventricular repolarization
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24
Q

What occurs during the PR interval?

A

Beginning of atrial excitation to beginning of ventricular excitation

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25
Q

What occurs during the ST segment?

A

Entire ventricular myocardium depolarized

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26
Q

What occurs during the QT segment?

A

Beginning of ventricular depolarization through ventricular repolarization

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27
Q

Identify the components of the ECG chart?

A
28
Q

Identify the rhythm

A

Normal

29
Q

Identify the rhythm

A

Ventricular fibrilation

30
Q

Identify the rhythm

A

Second degree heart block

31
Q

Identify the rhythm

A

Junctional rhythm

32
Q

What is Automaticity?

A

ability of pacemaker cells to generate an electrical impulse to regulate heart rate in accordance to the body’s needs

33
Q

What is absolute refractory period?

A

Time after the firing of a nerve fiber during which the nerve fiber cannot be stimulated, regardless of strength of the stimulus applied

34
Q

What causes ischemia in regards to electrolyte imbalances?

A

Inappropriate Ca2+ entry and K+ exit from cardiomyocytes

35
Q

What are electrolyte imbalances that cause dysthymias?

A
  1. Hyponatremia and kalmia: Actute MI
  2. Hypomagnesia: Increased CHD mortality and sudden cardiac death
  3. Hypercalcemia: shortens QT inteval
36
Q

What is reentry?

A

Cycling of electrical impulses

Propagating impulse fails to die out after normal activation of the heart and persists

37
Q

Where does reentry take place?

A
  1. Myocardial tissue
  2. AV nodal cells
  3. Junctional tissue
  4. Ventricles
38
Q

What is required to intimate reentry?

A
  1. Areas of slow conduction
  2. Unidirectional conduction block
  3. Triggering stimulus
39
Q

What is the function of areas of slow conduction?

A

previously depolarized areas to repolarize adequately to conduct an impulse again

40
Q

What is the function of unidirectional conduction block?

A

Provides one-way route for original impulse to re-enter, thereby blocking other impulses entering from the opposing direction and extinguishing the reentrant circuit

41
Q

What is the purpose of triggering stimulus?

A

Extrasystole to start the circuit

42
Q

What is cardiac arrest?

A

Abrupt loss of cardiac function

43
Q

What is considered normal conduction?

A

impulses from all Purkinje fibers collide in the ventricle and extinguish themselves → ventricular depolarization

44
Q

What causes reentry?

A
  1. Ischemia
  2. Infarction
  3. Elevated serum K+ levels
  4. Scar issue
45
Q

How can scar tissue cause dysrhythmias?

A
  1. Interrupts normally low-resistance paths between viable myocardial cells
  2. Slows conduction
  3. Promotes asynchronous myocardial activation
  4. Predisposes to unidirectional conduction block
46
Q

What is anatomic reentry?

A

Involves anatomic obstacle around which the circulating current must pass → an excitation wave the travels to set pathway

47
Q

What are the outcomes of anatomic reentry?

A

Arrhythmias: PSVTs, A fib, atrial flutter, AV nodal reentry, some ventricular tachycardias

48
Q

What is functional reentry?

A

Depends on local differences in conduction velocity and refractionaries among neighboring fibers that allow an impulse to circulate repeatedly around an area

49
Q

What are the manifestations of functional reentry?

A

Spinal reentry: wave of current does not propagate normally after meeting refractory tissue

Arrhythmias are polymorphic

50
Q

What is reflection reentry>

A

Occurs in parallel pathways of myocardial tissue or of the Purkinje network

51
Q

How does reflection reentry differ from true reentry?

A

The impulse travels along the same pathway in both directions and does not require a circuit

52
Q

What are the categories of peri-infarction dysrhythmias?

A
  1. Supraventricular tachydysrhthmias
  2. Accelerated junctional rhythms
  3. Ventricular dysrhythmias
  4. Intraventricular blocks
  5. Bradydysrhythmias
53
Q

Fast heart rate leads to ___

A

Sufficient ventricular filling

54
Q

Slow heart rate leads to ___

A

Sufficient perfusion

55
Q

Absent heart rate leads to ___

A

Pulseless VT or VF → cardiac arrest

56
Q

What are the presentations of Supraventricular tachydysrhythmias?

A
  1. Sinus tachycardia
  2. Premature atrial contractions (PACs)
  3. Paroxysmal supraventricular tachycardia (PSVT)
  4. Atrial flutter
  5. A fib
57
Q

What is A fib?

A

Atria to beat a rapid, irregular rate → pooling and clotting of blood → MI or stroke → Mortality

58
Q

Identify the difference?

A

Atrial flutter; A fib

59
Q

What is Accelerated junctional rhythms?

A

Junctional rhythms → Increased automaticity of AV junction tissue and escape rhythm

Inferior MI

60
Q

What are the presentation of ventricular dysrhythmia?

A
  1. Premature ventricular contractions (PVCs)
  2. Ventricular tachycardia (VT)
  3. Ventricular fibrillation (VF)
61
Q

What causes ventricular dysrhythmias?

A
  1. Electrical instability related to electrolyte imbalances
  2. Cardiomyopathies related to ischemia or nonischemic causes, structural problems, or heart failure
62
Q

What are the types of intraventricular blocks?

A

RBBB, LBBB

63
Q

What is RBBB?

A

Conduction delay that occurs in any part of the right-sided intraventricular conduction system → Death from cariogenic shock

64
Q

What is LBBB?

A

conduction delay or block from any of the several intraventricular conduction system sites → Reduced survival rates

65
Q

What are the types of Bradydysrhythmias?

A
  1. Sinus bradycardia
  2. First-degree AV block
  3. Second degree AV block
  4. Third degree AV block
66
Q

What are the types of second degree AV block?

A

1.Mobitz type I – commonly associated with an inferior MI
2. Mobitz type II – commonly associated with an anterior wall MI

67
Q

What is third degree AV block?

A

anterior and inferior MI

Most concerning

High mortality rate

Drug Action I (32 decks)

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