Intro to Antiarrhythmics Drugs - Nordgren Flashcards

1
Q

What is an Arrhythmia?

A
  • Any condition of the heart in which the electrical activity is:
    • Faster (tachycardia)
    • Slower (bradycardia)
    • Irregular
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2
Q

Normal cardiac rhythm depends on what three things?

A
  1. Impulse site of origin
  2. Rate of impulse
  3. Conduction (Transport) of Impulse
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3
Q

What is the Potassium Equilibrium Potential?

Electrochemical movement?

A

-90mV

  • Charge (electro):
    • K+ wants to move into cell
  • Concentration (chemical):
    • K+ want to leave cell
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4
Q

What is the Sodium Equilibrium Potential?

Electrochemical movement?

A

+70mV

  • Charge (electro):
    • Na+ wants to leave cell
  • Concentration (chemical):
    • Na+ want to move into cell
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5
Q

What effect will inhibiting the sodium channels have on the action potential of the cardiac cell?

A
  • Fast response/Contractile Myocytes:
    • elongates depolarization (phase 0)
    • slows conduction
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6
Q

What effect will inhibiting the potassium channels have on the action potential of the cardiac cell?

A
  • Prolong repolarization (phase 3)
    • Slows repolarization
    • Increases AP duration
    • Increases refractory period
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7
Q

What effect will inhibiting the calcium channels have on the action potential of the cardiac cell?

A
  • Fast Response/Cardiac Myocytes:
    • Shortens plateau of AP (phase 2)
    • Reduces force of contraction
      • Less Ca2+ available to bind troponin
  • Slow Resonse/Pacemaker cells:
    • Slows rise of AP (phase 0)
      • consequently prolongs repolarization at AV node → Decreased conduction velocity
    • Takes longer to reach threshold → Decreased HR
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8
Q

Atrial, Purkinje, and Ventricular Cells are dependent on what ion current for depolarization?

A

Na+

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9
Q

SA and AV nodal cells are dependent on what ion current for depolarization?

A

Ca2+

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10
Q

What are the three states of voltage gates in an active cell membrane?

A
  • Resting
    • activation gate closed
    • inactivation gate open
  • Activated
    • both activation and inactivation gates open
  • Inactive
    • activation gate open
    • inactivation gate closed
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11
Q

What is the key factor in pathophysiology of arrhythmias and the drugs used to treat them?

A

Relation between RESTING potential of a cell and the number of ACTION POTENTIALS that can be evoked.

  • membrane potential determines how many channels are open
    • e.g. Na+ channel inactivation gates close between -75 and -55 mV
      • if AP is evoked at -60mV, fewer Na+ channels will be available for diffusion of Na+ than if the AP occurred at -80mV
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12
Q

What factors lead to arrhythmia?

A
  • Many factors… but they all lead to arrhythmia through disturbances of either:
    • 1)Impulse Formation
    • 2) Impulse Conduction!
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13
Q

What effect do Na+-channel blockers have on the pace-maker rate, refractory period, and velocity of conduction?

A
  • Alters AP duration & kinetics of Na+ channel blockade
    • Steady-state reduction in # of available unblocked channels, which reduces excitatory currents to a level below that required for propagation
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14
Q

What effect do Ca2+-channel blockers have on the pace-maker rate, refractory period, and velocity of conduction?

A
  • Slows conduction where depolarization is Ca2+ dependent
  • Steady-state reduction in # of available unblocked channels, which reduces excitatory currents to a level below that required for propagation
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15
Q

What effect do K+-channel blockers have on the pace-maker rate, refractory period, and velocity of conduction?

A
  • Prolongation of the effective refractory period
  • Prolongation of recovery time of the channels still able to reach the rested and available state, which increases refractory period
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