Anti-arrhythmic Medications:
The Vaughan Williams Classification is the most used classification
of antiarrhythmics which classifies agents into 4 main classes:
• Class 1 = Sodium channel blockers
• Class 2 = Beta blockers
• Class 3 = Potassium channel blockers
• Class 4 = Calcium channel blockers
01) What is the mechanism of action of Procainamide and
Disopyramide for the treatment of arrhythmias?
• Procainamide and Disopyramide are Class 1A group of anti
arrhythmic in the Vaughan Williams classification.
• They work by blocking open and inactivated sodium channels in
the cell membrane to reduce the rate of Phase 0 depolarisation.
This causes an increase in the effective refractory period and
slowed AV conduction
Side effects of Class 1A anti-arrhythmic are atropine-life effects:
• Blurred vision
• Dry mouth
• Constipation
• Urinary retention
02) What is the mechanism of action of Lidocaine and Mexiletine for
the treatment of arrhythmias?
• Lidocaine and Mexiletine are Class 1B group of anti arrhythmic in
the Vaughan Williams classification
• They work by blocking sodium influx during Phase 0 which
depresses the rate of depolarisation. It also shortens repolarisarion
and duration of the action potential (decreasing the refractory
period)
Side effects of Class 1B anti-arrhythmic are:
• Drowsiness
• Light-headedness
• Paraesthesia
• Sensory disturbances
• Hypotension
• Bradycardia
, 03) What is the mechanism of action of Flecainide and Propafenone
for the treatment of arrhythmia?
• Flecainide and Propafenone are Class 1C group of anti arrhythmic
in the Vaughan Williams classification
• They work by blocking open sodium channels. This reduces the
rate of depolarisation causing an increase in the refractory period
and slowed AV conduction
Side effects of Class 1C anti-arrhythmic are:
• the development of new arrhythmia
• aggravation of existing arrhythmias
04) What is the mechanism of action of Beta blockers e.g metoprolol,
propranolol, bisoprolol and esmolol for the treatment of arrhythmias?
• Metoprolol, propranolol, bisoprolol and esmolol are Class II anti
arrhythmic in the Vaughan Williams Classification
• They work by blocking beta-adrenergic receptor sites in the
conduction system of the heart. As a result, the ability of the SA
node to fire spontaneously is slowed. The ability of the AV node
and other cells to receive and conduct an electrical impulses to
nearby cells (conductivity) is also reduced
- Class II antiarrhythmics also reduce the strength of the heart’s
contraction. When the heart’s beats less forcefully, it doesn’t
require as much oxygen to do it’s work
Side effects of Beta blockers are:
• Arrhythmias
• Bradycardia
• Heart failure
• Hypotension
• GI reactions e.g nausea, vomiting and diarrhoea
• Bronchoconstriction
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