The Vaughan-Williams classification is a way of dividing anti-arrhythmic drugs into groups based on their mechanism of action. It was devised in the 1970s, and like some other inventions of that era (such as flares) it has a few flaws. The main flaw is that many anti-arrhythmics actually work in several different ways, so although they can be put into a class based on their main mechanism of action this grouping only tells you part of how they work.
However, understanding it a) makes you seem clever (most consultants would have forgotten it within hours of passing MRCP) and b) helps you answer MRCP questions correctly. So lets ignore its faults and embrace it whole-heartedly...
The original classification had groups I, II, III and IV. A 'catch all' group of V has now been added for awkward drugs who just didn't fit in anywhere originally. Lets look at each class in turn:
Class Ia:
- works by blocking sodium channels - called a 'membrane stabiliser'
- distinguishes itself from the other class Is by having intermediate association/dissociation with the sodium channels --> end result longer action potential
- members include disopyramide, quinidine and procainamide
Class Ib:
- works by blocking sodium channels - called a 'membrane stabiliser'
- distinguishes itself from the other class Is by having fast association/dissociation with the sodium channels --> end result shorter action potential
- members include lidocaine and phenytoin
Class Ic:
- works by blocking sodium channels - called a 'membrane stabiliser'
- distinguises itself from the other class Is by having slow association/dissociation with the sodium channels --> end result same action potential
- members include flecanide and propafenone
Class II:
- are beta blockers
- I'm sure you don't really need examples but think atenolol, bisoprolol, misoprolol...
Class III:
- works by blocking potassium channels
- this results in prolonged repolarisation
- members include amiodarone and sotolol
Class IV:
- works by blocking calcium channels
- members include verapamil and diltiazem
(Class V: = last minute 'catch all', includes digoxin and
adenosine)
Thats rather a lot to try and remember; understanding and linking it to the cardiac action potential makes it a bit easier to understand, then a bit of word-play might clarify things further:
To remember the broad classes of drugs, try recalling 'Sodium Blocks Potassium Channels' (just substitute calcium for channels and you have the 4 mechanisms of action)
To remember the members of each class, think "
Double
quarter
pounder,
lemonade
please,
fries
please...
and
salt uh oh
vomiting and
diarrhoea..."
Got it? Good, cos you'll need in for
battle 7.3, long QT.
