Intro to Antiarrhythmics Drugs - Nordgren Flashcards
What is an Arrhythmia?
- Any condition of the heart in which the electrical activity is:
- Faster (tachycardia)
- Slower (bradycardia)
- Irregular
Normal cardiac rhythm depends on what three things?
- Impulse site of origin
- Rate of impulse
- Conduction (Transport) of Impulse
What is the Potassium Equilibrium Potential?
Electrochemical movement?
-90mV
- Charge (electro):
- K+ wants to move into cell
- Concentration (chemical):
- K+ want to leave cell
What is the Sodium Equilibrium Potential?
Electrochemical movement?
+70mV
- Charge (electro):
- Na+ wants to leave cell
- Concentration (chemical):
- Na+ want to move into cell
What effect will inhibiting the sodium channels have on the action potential of the cardiac cell?
- Fast response/Contractile Myocytes:
- elongates depolarization (phase 0)
- slows conduction
What effect will inhibiting the potassium channels have on the action potential of the cardiac cell?
- Prolong repolarization (phase 3)
- Slows repolarization
- Increases AP duration
- Increases refractory period
What effect will inhibiting the calcium channels have on the action potential of the cardiac cell?
- 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
- Slows rise of AP (phase 0)
Atrial, Purkinje, and Ventricular Cells are dependent on what ion current for depolarization?
Na+
SA and AV nodal cells are dependent on what ion current for depolarization?
Ca2+
What are the three states of voltage gates in an active cell membrane?
- Resting
- activation gate closed
- inactivation gate open
- Activated
- both activation and inactivation gates open
- Inactive
- activation gate open
- inactivation gate closed
What is the key factor in pathophysiology of arrhythmias and the drugs used to treat them?
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
- e.g. Na+ channel inactivation gates close between -75 and -55 mV
What factors lead to arrhythmia?
- Many factors… but they all lead to arrhythmia through disturbances of either:
- 1)Impulse Formation
- 2) Impulse Conduction!
What effect do Na+-channel blockers have on the pace-maker rate, refractory period, and velocity of conduction?
- 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
What effect do Ca2+-channel blockers have on the pace-maker rate, refractory period, and velocity of conduction?
- 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
What effect do K+-channel blockers have on the pace-maker rate, refractory period, and velocity of conduction?
- 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