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COM CPR E1 > 13. APs and Conduction > Flashcards

13. APs and Conduction Flashcards

1
Q

Describe the conduction system of the heart

A

SA node (60 ms) → AV node (100 ms) → Bundle of His (10 ms) → R/L Bundle Branches → Purkinje Fibers

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2
Q

what is the purpose of slow conduction through the AV node

A

slow conduction to allow time for ventricles to fill

increasing conduction velocity → decreased CO and SV

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3
Q

what physiologically makes the SA node the pacemaker of the cell

A

fastest rate of phase 4 depolarization, shortest AP duration and refractory period)

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4
Q

which parts have the greatest conduction velocity

A

larger diameter fibers are faster

purkinje > atrial and ventricular muscles > AV node

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5
Q

what is the purpose of overdrive suppression

A

to prevent the latent pacemakers (AV node, bundle etc) from driving HR

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6
Q

APs of ventricles, atria, and purkinjes: phase 0

  • what is it
  • what ions are responsible
  • why doesnt the membrane potential reach the ion potential
  • membrane potential at peak
A
  • upstroke, rapid depolarization
  • increase in Na conductance → inward Na current
  • inactivation gate closing prevents membrane potential from reaching Na potential
  • peak of upstroke, membrane potential = 20 mv
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7
Q

APs of ventricles, atria, and purkinjes: phase 1

  • what is it
  • what ions are responsible
A
  • initial repolarization
  • inactivation gates of Na channels close, decreasing inward Na current
  • outward K current
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8
Q

APs of ventricles, atria, and purkinjes: phase 2

  • what is it
  • what ions are responsible
A
  • plateau, long period of relatively stable depolarized membrane potential
  • increased Ca conductance → inward Ca current
  • outward K current balances Ca current
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9
Q

APs of ventricles, atria, and purkinjes: phase 3

  • what is it
  • what ions are responsible
A
  • repolarization
  • decrease in Ca conductance → decrease inward Ca current
  • increase in K conductance → increase outward K current
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10
Q

APs of ventricles, atria, and purkinjes: phase 4

  • what is it
  • what ions are responsible
A
  • resting membrane potential (-85 mv)

- outward K current balanced by inward Na and C currents

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11
Q

which ion current is known as the inward rectifier

A

I K1

close in response to depolarization, slow to close and remain open for a determined amount of time, then opens to help with phase 3

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12
Q

APs of SA Node: phase 0

  • what is it
  • what ions are responsible
A
  • upstroke

- increased Ca conductance → inward Ca current

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13
Q

APs of SA Node: phase 3

  • what is it
  • what ions are responsible
A
  • repolarization

- increased in K conductance → outward K current

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14
Q

APs of SA Node: phase 4

  • what is it
  • what ions are responsible
A
  • spontaneous depolarization or pacemaker potential

- funny Na channels → inward Na current

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15
Q

describe absolute refractory period

A
  • no APs can be generated

- most of Na channels are closed

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16
Q

describe relative refractory period

A
  • APs can be generated but requires greater stimulation
  • Na channels start to be available to carry inward currents
  • second AP will have abnormal configuration, shortened plateau phase, and will be weaker
17
Q

describe supranormal period

A
  • cell is more excitable than normal and easier to generate an AP, may have abnormal conduction and AP will be weaker
  • requires less inward current to depolarize cell
  • Na channels are recovered (inactivations gates open again)
18
Q

what is a +/- chronotropic effect?

A
  • change in HR, slope of depolarization in phase 4 of SA node

+ : increased HR by increasing phase 4 depolarization, increase If (S)

  • : decreased HR by decreasing phase 4 depolarization, decrease If (PS)
19
Q

what is a +/- dromotropic effect?

A
  • change in conduction velocity, slope of phase 0

+ : increased velocity, increased inward Ca current (S)

  • : decreased velocity, decrease inward Ca current, increased outward K current (PS)
20
Q

what effect would a +/- dromotropic effect have on the PR interval

A

+ : decreased PR interval

  • : increased PR interval
21
Q

what is an ionotropic effect? lusitropic?

A

Ionotropic- effects strength of muscular contraction

Lusitropic- effects rate of muscular relaxation

22
Q

what effect does the parasympathetic system have on HR

A
  • chronotropic effect: slower opening of funny Na channels during phase 4
  • dromotropic effect: reduced inward Ca current, increase outward K current via special K-ach

PS: vagus nerve, ach → muscarinic (M2/M3)
innervates SA and AV node
no ionotropic or lusitropic influence

23
Q

what effect does the sympathetic system have on HR

A

+ chronotropic effect: more rapid opening of funny Na channels during phase 4
(beta agonist meds increase rate of phase 4 depolarization by increasing If, beta antagonists decrease)

+ dromotropic effect: increased inward Ca current

S: NE → B1
innervates SA node, AV node, ventricular myocytes (not atrial)
positive ionotropic or lusitropic influence

24
Q

what is the key difference in phase 4 of AP found in SA/AV node vs myocytes

A
  • rmp gradually depolarizes until it reaches threshold

- d/t funny Na channels that open upon complete repolarization of membrane

25
Q

what is the key difference in phase 0 of AP found in SA/AV node vs myocytes

A
  • opening of voltage gated Ca channels rather than voltage gates Na channels
  • closure of voltage gated K channels (rectifies)
26
Q

what is the key difference in phase 3 of AP found in SA/AV node vs myocytes

A
  • reversal of phase 0

- closure of voltage gated Ca channels and opening of voltage gated K channels (both rectifiers and traditional)

27
Q

which phase of the AP corresponds with the QRS complex?

T wave?

ST segment?

A

QRS: phase 0; rapid depolarization, influx of Na

T: phase 1/3, repolarization, efflux of K

ST: phase 2, plateau, influx of Ca = efflux of K

COM CPR E1 (20 decks)

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