Anti-arrhythmias

Question 1

what are the four important anti arrhythmia drugs to remember

Answer 1

metoprolol, amiodarone, diltiazem, digoxin

Question 2

what are the four classes of anti-arrhythmia drugs

Answer 2

class one: drugs that interfere with the Na+ channels
class two: beta blockers
class three: agents that reduce K+ efflux
class four: calcium channel blockers
then there’s the others

Question 3

what drugs dont fit the vaughn williams classifications

Answer 3

Digoxin, Adenosine, Atropine

Question 4

whats an example of a class one anti arrhythmia drug

Answer 4

lignocaine

Question 5

how does lignocaine work

Answer 5

it antagonises the fast acting Na+ channels that are involved in the upstroke of cardiomyocytes. the effect is that the cells depolarise more slowly so their conduction velocity is less.

Question 6

ADR of lignocaine

Answer 6

the slower conduction can actually induce arrthymia

Question 7

example of a class 3 anti arrhythmia drug

Answer 7

that would be amiodarone

Question 8

how does amiodarone work

Answer 8

it has a range of effects:
it can block the K+ efflux pumps, prolonging the membrane repolarisation.
also has an effect on the Ca2+ channels causing an increased plateau period
so contractility is unchanged or increased with the increased AP length in the cardiac muscle

Question 9

uses of amiodarone

Answer 9

it is good for rate control in AF. its good to use when the patient may still want to maintain exercise capabilities

Question 10

why are the calcium channel blockers good in atrial fibrillation

Answer 10

they decrease the rate of action potential generation in the cardiac pacemaker cells, slow conductance at the AV node
in the cardiomyocytes they depress contraction via inhibition of the Ca2+ L type channels

Question 11

how does digoxin work

Answer 11

via two mechanisms
1: it is an inhibitor of Na+/K+ ATPase. as cardiomyocytes have an Na+/Ca2+ exchanger, the excess Na+ is moved out for more Ca2+, this results in an increased force of contraction in the cardiac cell
2: it increases ACh release to the SA node via the PNS, to make vagal relaxation effect

Question 12

why can digoxin end up being dangerous

Answer 12

it can cause arrhythmia,

Question 13

what do we do incase of digoxin overdose

Answer 13

Withhold the digoxin! Also K+-sparing diuretics.
Keep track of serum [K+]
Administer antidysrrhythmic drugs
lidocaine
atropine
Neutralize digoxin
◦ Fab antibody fragments
◦ Cholestyramine
◦ activated charcoal