Antiarrhythmic drugs Flashcards
What is the rhythm of the heart determined by?
Pacemaker cells
Where do supraventricular arrhythmias originate?
AV node or atrial myocardium
Where do ventricular arrhythmias arise from?
Ventricles
What can cause an arrhythmia?
Ectopic focus - starts firing at a hgiher rate than a normal pace maker
Re-entry mechanisms - delayed action potentials re-invade nearby muscle fibres causing a loop of depolarisation
What are arrhythmias assciated with stress (increase in emotion, exercise, MI, thyrotoxicosis) treated with?
Beta-blockers
What is an arrythmia that is common after an MI?
Sinus bradycardia
Drugs used in supraventricular arrhythmias?
- adenosine
- digoxin
- verapamil
Drugs used in ventricular arrhythmias?
Class IB
- lidocaine IV
- mexiletine
Drugs used in both supraventricular and ventricular?
Class IA - disopyramide - procainamide Class IC - flecainide Class III - amiodarone - sotalol
What does Class IA target?
Voltage-activated Na+ channels
What does Class IB target?
Voltage-activated Na+ channels
What does Class IC target?
Voltage-activated Na+ channels
What does Class II target?
B-adrenoceptor (as antagonists)
What does Class III target?
Voltage-activated K+ channels
What does Class IV target?
Voltage-activated Ca2+ channels
What is the order that class IA, IB and IC drugs dissociate from Na+ channels? fastest -> slowest
IB - rapid rate
IA - moderately slow
IC - slow rate
What is the function of Class II drugs?
decrease rate of depolarisation in SV and AV nodes
What is the function of Class III drugs?
prolong the action potential duration which increases the refractory period
What is the function of Class IV drugs?
slows the conduction in SA and AV nodes
decreases force of contraction
What is the function of Class IA drugs?
Slows the rate of rising action potential and prolonges refractory period
What is the function of Class IB drugs?
Prevents premature beats
What is the function of Class IC drugs?
Depresses conduction
