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Block 3 > HRR: Pacemakers And Electrical Conduction > Flashcards

HRR: Pacemakers And Electrical Conduction Flashcards

1
Q

What is the electrical connection between the atria and ventricles under normal conditions?

A

AV node

The AV node serves as a critical pathway for electrical signals between the atria and ventricles.

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2
Q

Describe the electrical flow through the heart.

A

SA node > AV node > bundle of His > right/left bundle branch > His-Purkinje system

This sequence outlines the conduction pathway that regulates heartbeats.

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3
Q

What are intermodal conduction pathways?

A

They are specialized conduction pathways in the atrium that connect the SA node to areas of the atrium

These pathways facilitate rapid electrical conduction across the atrial tissue.

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4
Q

Are gap junctions unidirectional or bidirectional?

A

Bidirectional!

This allows electrical signals to pass freely between adjacent cardiac cells.

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5
Q

What are the elements of intercalated discs?

A

Gap junctions and cadherins/connexins

These structures connect adjacent cells and allow for synchronized contraction.

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6
Q

What allows for unidirectional conduction?

A

Cells becoming refractory

This refractory period prevents re-excitation and ensures organized electrical activity.

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7
Q

What kind of cells make up the SA node?

A

Specialized myocyte with high automaticity

These cells are responsible for initiating the electrical impulses of the heart.

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8
Q

Describe the distribution of Purkinje cells.

A

They branch into multiple places in the endocardium of ventricles

This extensive branching allows for rapid conduction of impulses throughout the ventricles.

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9
Q

Compare phase 4 in working myocyte and nodal myocyte.

A

Phase 4 in working myocyte is flat at around -89/-90 mV; in nodal myocyte, it is sloped and around -60/-50 mV

This difference reflects the distinct functions of these myocytes in electrical conduction.

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10
Q

What makes phase 4 more unsteady in nodal myocyte?

A

Funny currents, acetylcholine-dependent potassium channel, and T-type calcium channels

These factors contribute to the automaticity of nodal myocytes.

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11
Q

What is necessary for funny currents to activate?

A

Hyperpolarization

This condition allows for the influx of sodium ions, initiating the depolarization phase.

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12
Q

Compare phase 0 in working myocytes and nodal myocytes.

A

Phase 0 in working myocytes shows rapid depolarization; in nodal myocytes, it is slower due to L-type calcium current

This difference is crucial for the timing of heartbeats.

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13
Q

What occurs during phase 1 in working myocytes?

A

Early repolarization occurs

Phase 1 is absent in nodal myocytes.

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14
Q

What characterizes phase 2 in working myocytes?

A

A plateau due to L-type calcium channels

Phase 2 is absent in nodal myocytes.

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15
Q

How do phase 4 characteristics differ between working myocytes and nodal myocytes?

A

Both show repolarization, but nodal myocytes experience a period of hyperpolarization

Working myocytes do not have this hyperpolarization.

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16
Q

What is the major repolarizing current in cardiac myocytes?

A

Potassium

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17
Q

What does automaticity in cardiac myocytes depend on?

A

Threshold rate, hyperpolarization degree, duration of depolarization

It also includes the corresponding refractory period.

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18
Q

How does the PSNS impact SA nodal action potential?

A

M2 stimulation increases outward potassium, leading to hyperpolarization

This results in a slower firing rate.

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19
Q

What effect does the SNS have on SA nodal action potential?

A

Increases sodium and calcium channel activity, resulting in a quicker threshold reach

This increases the firing rate.

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20
Q

What are some factors that cause bradycardia?

A
  • Hypothyroidism
  • Hyperkalemia
  • Hypoxia
  • Calcium channel blockers
  • Muscarinic agonists
  • Beta-blockers
  • Digitalis in therapeutic doses
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21
Q

What are some factors that cause tachycardia?

A
  • Hyperthyroidism
  • Hypokalemia
  • Muscarinic antagonists
  • Epinephrine
  • Digitalis in toxic doses
22
Q

Where is conduction velocity at its slowest?

A

The AV node

23
Q

Where is conduction velocity at its fastest?

A

In the ventricles

24
Q

What is the secondary pacemaker if the SA node fails?

A

The AV node

This results in a slower heart rate due to reduced conduction velocity.

25
Q

How long does it take for the signal to travel from the SA node to the AV node?

A

30 ms

26
Q

How long does the signal stay at the AV node?

A

90 ms

27
Q

How long does it take for the signal to travel from the AV node to the bundle of His?

A

40 ms

28
Q

How long does it take for the signal to reach Purkinje fibers?

A

40 ms

29
Q

How long does it take for the signal to reach the apex?

A

60 ms

30
Q

How long does ventricular repolarization last?

A

300 ms

31
Q

Where does SA node firing show up on EKG?

A

It doesn’t show up

32
Q

What does the P wave on an EKG represent?

A

Atrial depolarization

33
Q

What is the PR interval?

A

Impulse traveling from SA node to AV node and bundle of His

34
Q

What does the QRS complex represent?

A

Ventricular depolarization

35
Q

In what order do the layers of the heart reach action potential?

A

Endocardium > mid-myocardium > epicardium

36
Q

Why does an EKG show a 0 voltage after the QRS complex?

A

Each layer is in the plateau stage of action potential; this is called the ST segment

37
Q

What is the QT interval?

A

Ventricular repolarization

38
Q

In what order do the layers of the heart repolarize?

A

Epicardium > mid-myocardium > endocardium

39
Q

What does the T wave represent?

A

Repolarization of the ventricle

40
Q

Why do we not see atrial repolarization on an EKG?

A

It occurs during the QRS complex and is masked by ventricular depolarization

41
Q

How long is the PR interval?

A

.12-.20 sec

42
Q

How long is the QRS interval?

A

.06-.12 sec

43
Q

How long is the QT interval?

A

.4-.43 sec

44
Q

How long is the RR interval?

A

0.6-1.0 sec

45
Q

What is the heart rate (HR) when the AV node is in charge?

A

40-60 bpm

46
Q

What is the heart rate (HR) when the His-Purkinje system is in charge?

A

15-40 bpm

47
Q

What determines which cells become the primary pacemaker?

A

Whichever is fastest takes over

48
Q

What are some issues that can occur with pacemaker cells?

A
  • Failure to generate impulse
  • Conduction delay or interruption
  • Reentry
49
Q

Describe the process of reentry in pacemaker cells.

A

Impulse comes to a cell, passes to a cell below it, moves downstream, and then moves backwards to the cell that did not get depolarized.

50
Q

What is needed for reentry to occur?

A
  • An alternate pathway
  • Slow anterograde conduction
  • Cells proximal to the slow pathway cannot be refractory

Block 3 (52 decks)

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