Antiarrhythmia drugs Flashcards
what is the mechanism of class I anti-arrhythmia drugs
Block Na channels
Reduce phase 0 slope and Action potential peak
what is the mechanism of action of class Ia anti-arrhythmia drugs
Produce an action potential duration above the control, it prolongs the AP and should prolong the effective refractory period
what is the mechanism of action of class Ib anti-arrhythmia drugs
Produce an action potential below the control – shorter AP and short ERP
what is the mechanism of action of class Ic anti-arrhythmia drugs
No large effect on action potential duration or ERP
what is the mechanism of action of class II anti-arrhythmia drugs
Beta-blockers
They block the sympathetic drive and reduce the rate of conduction and excitability
what is the mechanism of action of class III anti-arrhythmia drugs
K-channel blockade
They delay repolarization
Increase action potential duration and effective refractory period
what is the mechanism of action of class IV anti-arrhythmia drugs
Ca channel blockers
Most effective in nodal tissue by reducing the rate and conduction
Give an example of a class Ia anti-arrhythmia drug and where it acts
Quinidine
Works on the atrial muscle and bypass tract and the ventricles
How does Quinidine function
Decreases sodium entry into the cell - it binds to inactivated Na channel in a use dependant way
It prolongs APD and reduces upstroke
When is Quinidine used
Ventricular arrhythmia
Prevention of paroxysmal recurrent atrial fibrillation (triggered by vagal overactivity)
Give an example of a class Ib anti-arrhythmia drug and where it acts
Lignocaine (lidocaine)
Acts on the ventricles
How does Lignocaine function
Decrease sodium entry into the cell
Decreases AP duration and reduce upstroke
It supresses automaticity by:
• Prolonging refractory period by binding to the inactive state
• Decreases conduction (especially in ischemic tissue)
• Decrease Na influx
When is Lignocaine used
For treatment (and prevention) during and immediatly after myocardial infarction
Ventricular tachycardias
Why is Lignocaine not used to treat myocardial infarction anymore
Increased risk of asystole
Give an example of a class Ic anti-arrhythmia drug
Propafenone
How does Propafenone function
Blocks sodium entry
Minimum change in AP duration
Supresses automaticity
INCREASE in refractory period
When is Propafenone used
Wolff-Parkinson-White syndrome
Recurrent tachyarrhythmias
When is Propafenone NOT used
It decreases cardiac contractility hence not advised immediatly post myocardial infarction
Give an example of a class II anti-arrhythmia drug and where it acts
Atenolol
Acts on the SA node, AV node, and Ventricle
What is the function of Atenolol
Beta-blocker Acts at the SA node Supresses automaticity by decreasing sympathetic drive: - Shortens AP duration - Prolongs refractory period - Decrease conduction in SA and AV node - Hemodynamic depression
when is atenolol used?
Supraventricular tachycardias
Improve survival post myocardial infarction
Give an example of a class III anti-arrhythmia drug and where it acts
Amiodarone
Acts on the atrial muscle, bypass tract and ventricle
What is the function of Amiodarone
K channel blockade
Prolong action potential
Prolong refractory period
What is amiodarone useful for
Wolff-Parkinson-White syndrome
Ventricular tachycardias
Atrial fibrilation
Give an example of a class IV anti-arrhythmia drug and where it acts
Verapamil
AV node
What is the function of Verapamil
Ca channel blockers
May reduce O2 demand and cardiac work
what is verapamil used for
Prevents the recurrence of paroxysmal supraventicular tachycardia
Reuces ventricular rate in patients with atrial fibrillation
Name two physiological agents used to treat arrythmias
Magnesium
Adenosine
How does magnesium function
Reduces calcium entry through the sarcolemma
When is magnesium depleted
in ishaemic cells
What is magnesium valuable in
Ventricular arrythmias
Ischemic cells especially if there is hypomagnesemia
What is the function of adenosine
enhances K current in atrial tissues
What is adenosine used for
supraventricular tachycardia
What are the side effects of adenosine
transient flushing
breathlessness
Give an example of a “class V” anti-arrhythmia drug
Digoxin
How does Digoxin function
Supresses AV conduction
Decreases ventricular rate
When is Digoxin used
supraventricular tachyarrhythmias
what are the side effects of Anti-arrhythmias
They may be pro-arrhythmic in 5-15% of people due to:
- Inhomogeneity (inequallness/not coordinated) in conduction and refractoriness
- Prolongation of action potential duration (EAD)
- Preexisting severe cardiomyopathy
