Anti-Arrhythmia Agents Flashcards
What are the 5 phases of the cardiac action potential?
0: Upstroke
1: Early-fast repolarization
2: Plateau
3: Repolarization
4: Diastole
Ion Movements Phase 0
Na influx
Ion Movements Phase 1
K efflux (Transient Outward)
Ion Movements Phase 2
Ca influx - counterbalances the K efflux to maintain a plateau period
Ion Movements Phase 3
K efflux (Delayed Rectifier)
Ion Movements Phase 4
Na/K ATPase Pump
What is the refractory period in atrial and ventricular myocytes determined by?
Voltage
What is the refractory period in pacemaker cells determined by?
Time
What are the general types of arrhythmias?
- Too fast
- Too slow
- Asynchronous
What are the causes of arrhythmias?
- disturbed impulse formation
- disturbed impulse conduction
- combination of 1 and 2
What are some examples of disturbed impulse formation?
Early afterdepolarization (EAD) Delayed afterdepolarization (DAD)
What are some examples of disturbed impulse conduction?
SA-block
AV-block
Re-entry
What are the requirements for re-entry?
- Slowed conduction
- Conduction block
- Unidirectional block
What are the aims of anti-arrhythmic therapy?
Aimed to reduce ectopic pacemaker activity and/or
modify conduction characteristics to disable re-entry circuits
Use-dependent or state-dependent drug action
Drug has highest binding affinities to the activated and inactivated channels with low to no affinity for the resting state.
What should be done for the treatment of asymptomatic or minimally symptomatic arrhythmias?
Treatment should be AVOIDED
Class I
Na+ Channel Blockers
Class II
ß-adrenoceptor blockers
Class III
Prolong AP Duration
Class IV
Ca2+ Channel Blockers
What is a secondary effect of Na+ Channel Blockers?
Local anesthesia
What is the general action of the Class I agents?
Reduction of conduction velocity by reducing rate and magnitude of depolarization via Na+ channel blockade.
May influence repolarization through effects on K+ channels which will prolong the AP duration.
Class I A
Intermediate kinetics, APD is increased
Class I B
Fast kinetics, APD is decreased
Class I C
Slow kinetics, APD remains the same
Examples of Class I A
Procainamide, Quinidine, Disopyramide
Examples of Class I B
Lidocaine, Mexiletine
Examples of Class I C
Flecainide, Propafenone
Procainamide Actions
- Slows upstroke of AP, conduction, prolongs QRS complex
- Direct depressant actions on SA and AV nodes
- More effective in depolarized cells (use/state dependent action)
Procainamide Indications
Atrial and ventricular arrhythmias - Drug of second or third choice though
Procainamide SE
Ganglion blocking properties,
Risk of hypotension
Anti-cholinergic effects
Induction of torsade de pointes arrhythmia
Quinidine Actions
Same as procainamide
- Slows upstroke of AP, conduction, prolongs QRS complex
- Direct depressant actions on SA and AV nodes
- More effective in depolarized cells (use/state dependent action)