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Cardiopulmonary > 1D: Cardiac Electrophysiology > Flashcards

1D: Cardiac Electrophysiology Flashcards

0
Q

What is the basis of the electrical activity of excitable cells?

A

Electrical potential differences across biological membranes are the basis of the electrical activity of excitable cells

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1
Q

What is the pathway of the SA node?

A

On the right side: SA NODE–>Internodal tract–>AV NODE–>AV bundle–>R/L Bundle Branches

On the left side : SA NODE–> Interatrial tracts

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2
Q

Describe excitable cells

A
  • Neurons
  • Muscle cells (skeletal, cardiac & smooth)
  • Cells comprising the cardiac conduction system
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3
Q

What does the appearance of the cardiac AP depend on?

A

Depends upon WHERE it is measured \

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4
Q

What are the 2 types of Cardiac AP’s?

A

1) Non-pacemaker or “fast response”

2) Pacemaker “slow response”

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5
Q

What are the Cardiac AP phases ?

A

O: Upstroke

1: Early phase repolarization
2: Plateau
3: Repolarization
4: Diastole

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6
Q

What is the Non-pacemaker or fast response?

A
  • occur in the atria ventricles & Purkinje fibers

- Undergo “rapid” depolarization

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7
Q

What is the pacemaker or “slow response”

A
  • Occurs in the SA node & AV node

- Undergo “slow” depolarization

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8
Q

What occurs in phase O (rapid depolarization) ?

A
  • Upstroke of the AP
  • “Fast” Na+ channels open
  • Several types of K+ channels close
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9
Q

What is Phase 1 ?

A

Early/Initial Repolarization

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10
Q

What occurs in Phase 1 (early/initial Repolarization)

A
  • Transient outward current as K+ channels open

- “Fast” Na+ channels are closed

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11
Q

What is phase 2?

A

plateau phase

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12
Q

What occurs in Phase 2 (plateau)

A
  • Long lasting (L -type ) Ca++ channels open leading to inward Calcium movement
  • Efflux of K+ thru several types of K+ channels
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13
Q

How does skeletal and cardiac contraction differ in their requirement for Ca++ influx during an AP?

A

Whereas exviation-contraction coupling in skeletal muscle does NOT require influx thru L-type Ca++ channels,
cardiac contraction has an absolute REQUIREMENT for Ca++ influx thru these channels during the AP .

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14
Q

Describe the amount of Ca++ entering the cardiac muscle cell during an AP

A

Amount is SMALL and does NOT promote actin-myosin interaction

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15
Q

What does the influx of calcium during an AP serve to trigger?

A
  • Induces calcium release form the Sarcoplasmic Reticulum. (**Calcium-induced calcium release = CICR) Which then promotes actin-myosin interaction and hence contraction;
  • This occurs via ryanodine receptors (RyR2)
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16
Q

What can alter calcium conductance?

A

-Neurotransmitters and drugs can alter conductance.

-NE increases
whereas Ach, B-blockers & Ca++ channel blockers decrease it!!!

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17
Q

What is phase 3?

A

Later or Final Repolarization

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18
Q

What occurs in Phase 3 (late or final Repolarization?)

A
  • Continual efflux of K+ thru several types of K+ channels

- L-type Ca++ channels eventually close

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19
Q

What is phase 4?

A

RMP Resting Membrane Potential

20
Q

What occurs in phase 4 (RMP) ?

A
  • K+ channels remain open

- Ca+ extrusion mechanisms become highly active

21
Q

What are the main calcium extrusion mechanisms ?

A

1) SR Ca++ pumps (SERCA)
2) Sarcolemmal Ca++ pumps
3) 3 Na+/1Ca++ exchangers (NCX)

22
Q

How do the electrical and mechanical events in cardiac muscle differ from the skeletal muscle?

A

The events in cardiac muscle overlap considerably in time, as \opposed to the skeletal muscle where the electrical even is over before the mechanical event begins

23
Q

True or False. It is impossible to produce the summation and tetanus found in skeletal muscle during high frequency stimulation in cardiac muscles?

A

True

24
Q

What would tetany of the heart lead to ?

A

Death

-The prolonged refractory periods (in part I) allow the ventricles to relax and fill with blood before the next contraction.

25
Q

What are refractory periods?

A

Once a fast response AP has been initiated, the depolarized cell is not longer excitable until the cell is partially repolarized.

26
Q

What is the effective or (absolute) refractory period?

A

a 2nd AP absolutely cannot be initiated, no mater how large the stimulus.

27
Q

What is the relative refractory period?

A

A 2nd AP may be evoked ONLY when the stimulus is sufficiently strong (supra-threshold)

28
Q

What is the SA node? (Sinoatrial)

A
  • Is the pacemaker of the heart
  • Has a unstable RMP
  • Exhibits phase 4 depolarization or Automaticity ( the ability to intiate its own AP)
29
Q

What is a slow response cardiac AP in phase O?

And what is it caused by?

A
  • The upstroke of the AP
  • Caused by an increase in Ca++ conductance
  • Result of an inward Na+ current
30
Q

In slow response cardiac action potential what is phase 3? And what is it caused by?

A
  • is Repolarization
  • Caused by an increase in K+ conductance; This increase results in an outward K+ current that causes Repolarization of the membrane potential
31
Q

What occurs in slow response cardiac AP, phase 4? and what is it caused by?

A

Is slow depolarization

  • accounts for the pacemaker activity of the SA node (automaticity)
  • caused by an increase in Na+ conductance, which results in an inward current called (I. f)
32
Q

What is (I. f ) turned on by?

A

The Repolarization of the membrane potential during the preceding AP

33
Q

Describe the cardiac conduction system of the SA Node

A

SA node of the right: SA Node–> internodal tracts–> AV node–>AV bundle–>R/L Bundle Branches–>Purkinje fibers

SA on the left: SA–> Interatrial tracts

34
Q

What is HR?

A

The number of times the SA node discharges per minute

35
Q

What is the Conduction velocity (CV)

A

reflects the time required for excitation to spread throughout cardiac tissue

36
Q

Where is CV (conduction velocity) the fastest? Where is it the slowest?

A

FASTEST In the Purkinje system
SLOWEST in the AV node (seen as the PR internal on the ECG)
-This allows time for ventricular filling before ventricular contraction.

37
Q

What happens if conduction velocity through the AV node is increased ?

A

Ventricular filling may be compromised

38
Q

1) What are Chronotropic effects?

a) What does a negative and b)postive Chronotropic effect do?

A

1) Produce changes in HR.
a) Negative- decreases HR by decreasing the firing rate of the SA node
b) Positive- increases the HR by increasing the firing rate of the SA node

***Changes in the HR are reflected on the ECG by changes in the R-R intervals

39
Q

What are Dromotopic effects?

A

-produces changes in conduction velocity, primarily in the AV node

40
Q

What does a negative and positive dromotropic effect do??

A

Negative dromotroptic effect- decreases conduction velocity thru the AV node slowing the conduction of AP from the atria to the ventricles & increasing the PR interval

Positive dromotropic effect- increases conduction velocity thru the AV node, speeding the conduction of APs from the atria to the ventricles & decreases the PR interval

41
Q

The SA node, atria, & AV node have ____________ vegal innervation, but the ventricles do not.

A

Parasympathetic

42
Q

The neurotransmitter for parasympathetic is _____________ which acts at muscarinic receptors

A

acetylcholine (ACh)

43
Q

The SA node, AV node, atria and ventricles have _____________ innervation. The neurotransmitter is _________________ which acts at Beta-1 receptors.

A

a) sympathetic innervation

b) Norepinephrine (NE)

44
Q

The parasympathetic effects on HR- What occurs during Negative chronotropic effect?

A
  • Decreasing HR by decreasing the rate of phase 4 depolarization
  • Fewer APs occur per unit time b/c the threshold potenital is reached more slowly and less frequently.
  • The mechanism of the negative chronotropic effect is decreased (I.f) the inward Na+ current is responsible for phase 4 depolarization in the SA node
45
Q

The parasympathetic effects on HR- What occurs during Negative Dromotropic effect?

A
  • Decreases conduction velocity thru the AV node.
  • APs are conducted more slowly from the atria to the ventricles
  • Increases the PR interval ****
  • The mechanism of the negative dromotropic effect is decreased inward Ca++ current and increased outward K+ current.
46
Q

The sympathetic effects on HR- What occurs during Positive chronotropic effect?

A

-Increases HR by increasing the rate of phase 4 depolarization

  • More AP occur per unit time because the threshold potential is reached more quickly and therefore more frequently
  • The mechanism of the positive chronotropic effect is increased (I. f), the inward Na+ current that is responsible for phase 4 depolarization in the SA node.
47
Q

The sympathetic effects on HR- What occurs during Positive dromotropic effect?

A
  • Increases conduction velocity thru the AV node
  • AP are conducted more rapidly from the atria to the ventricles & ventricular filing may be compromised.
  • Decreased the PR interval
  • The mechanism of the positive dromotropic effect is increased inward Ca++ current

Cardiopulmonary (19 decks)

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