Anti-arrythmics Flashcards
What is meant by inotropy?
Modification of the force of contraction
What is meant by lusitropy?
Modification of the rate of relaxation (Length of Diastole)
What is meant by Chronotropy?
Modification of heart rate
What is Torsades de pointes?
A highly irregular form of arrhythmia
What is an arrhythmia?
A condition where there are disturbances to the electrophysiology of the heart
What are the 2 causes of arrhythmias?
Abnormal impulse formation
Abnormal impulse conduction
What are the 2 types of abnormal impulse formation?
Triggered rhythm
Automatic rhythm
What are the 2 types of Triggered rhythm?
Ectopic foci - APs arise from sites other than the SA node
Enhanced normal automaticity - More AP from SA node
What are the 2 types of Automatic rhythm?
Delayed After-Depolarisations
Early After-Depolarisations (Phase 2&3)
What are the 2 types of abnormal impulse conduction?
Conduction Block
Re-Entry
What are the 3 main types of Conduction block?
1st degree
2nd degree
3rd degree
What is meant by a 1st degree conduction block?
AV delay >0.2 ms without disrupting the hearts function
What is meant by a 2nd degree conduction block?
Intermittent failure of the heart to conduct between SA and AV nodes
What is meant by a 3rd degree conduction block?
Complete loss of communication between the atria and ventricles
What are the 2 types of Re-entrant arrhythmia?
Circus movement
Reflection
What is meant by circus movement?
Circular motion of electrical impulses in the heart leading to fluttering
What is meant by reflection?
Movement of electrical impulses forwards from the atria to the ventricles, and then back down the same pathway
What are the 6 classes of Vaughn-Williams anti-arrhythmic drugs?
Class 1a
Class 1b
Class 1c
Class 2
Class 3
Class 4
What is meant by a class 1 anti-arrhythmic drug?
Sodium channel blocker:
a = Moderate strength
b = Weak
c = Strong
What is meant by a class 2 anti-arrhythmic drug?
ß-adrenoceptor blockers
What is meant by a class 3 anti-arrhythmic drug?
Potassium channel blocker
What is meant by a class 4 anti-arrhythmic drug?
Calcium channel blocker
How do class 1 (Sodium channel blockers) anti-arrhythmics work?
Na+ channel blockers slow the depolarisation of the myocytes, preventing contraction which occurs by opening of Na+ channels
What are the main uses of Class 1 (Na+ channel blockers) anti-arrhythmics?
They can be used in life-threatening ventricular arrhythmias, ischaemic tissue and inherited long QT syndrome
What are some examples of Class 1 (Na+ channel blockers) anti-arrhythmics?
Lidocaine
Mexilitine
How does lidocaine work?
Lidocaine is a type 1b anti-arrhythmic and a local anaesthetic
It only blocks inactive or open channels, so blocks damaged, depolarised tissue
It blocks during depolarisation and then rapidly dissociates
How do Class 2 (ß-adrenoceptor blockers) anti-arrhythmics work?
ß1 adrenoceptors are bound to GßY and Gαs
Gαs ad GTP activates adenylyl cyclase
This converts AMP to cAMP
cAMP increases protein kinase A levels
Protein Kinase A leads to a shorter funny current
ß-adrenocpetors stop this and so increase the length of the funny current
What are the 2 types of ß-blockers?
Cardio selective
Non-selective
What are some examples of Cardio selective ß-blockers?
Atenolol
Bisoprolol
Carvedilol
Metoprolol
What are some examples of non-selective ß-blockers?
Propranolol
Soltalol
Why should asthmatics not be given non-selective ß-blockers?
They also act on ß2-adrenoceptors and thus can cause bronchospasm
What are the main uses of Class 2 (ß-adrenoceptor blockers) anti-arrhythmics?
They can be used to manage non-sustained ventricular arrhythmias, atrial tachycardia, angina and hypertension
What are the risks of Type 3 (K+ channel blockers) anti-arrhythmics?
They are extremely difficult to manage and can lead to Torsades de pointes, meaning they are only used in those who have tried other treatments
How do Class 3 (K+ channel blockers) anti-arrhythmics work?
They decrease the probability of K+ influx leading to depolarisation.
This increases the length of the plateau in myocytes and thus, increases the length of the refractory period
What is an example of a Class 3 (K+ channel blocker) anti-arrhythmic?
Amiodarone (Also has Class 1,2 and 4 actions)
How can some Class 3 anti-arrhythmic become pro-arrhythmic?
Lengthening the refractory period should prevent another action potential occurring too soon, however, some can prolong the QT interval and thus become pro-arrhythmic
What are some main uses of amiodarone?
It prolongs the action potential, mainly by blocking K+ channels, this can suppress tachyarrhythmias due to re-entry and can be used in atrial fibrillation
How do Class 4 (Ca2+ channel blockers) anti-arrhythmic drugs work?
They block Ca2+ influx in the pacemaker cells of the SA node
This causes a delay in the depolarisation phase and extends the refractory period
What are some examples of class 4 (Ca2+ channel blockers) anti-arrhythmic drugs
Verapamil
Diltiazem
What are the main uses of Class 4 anti-arrhythmics?
They decrease aberrant pacemakers, conduction velocity and depolarisation
This blocks re-entrant rhythms such as supra ventricular tachycardia
Where do Atrial and supra-ventricular arrhythmias occur?
In the Sino-Atrial or Atria-Ventricular Node
Where do Ventricular arrhythmias occur?
In the common Bundle of His, bundle branches or Purkinje fibres
What is atrial fibrillation?
A supra-ventricular tachyarrhythmia with uncoordinated atrial electrical activation and thus ineffective atrial contraction
What is meant by a paroxysm?
A sudden attack or occurrence of symptoms
How does Ivabradine work?
It blocks HCN Na+ channels and thus elongates the funny current
How does Adenosine work?
It is a natural nucleoside that binds to adenosine A1 receptors
It alters opening of some K+ and Ca2+ channels
This slows AV nodal conduction
It also hyperpolarises the cell
