Antidysrhythmics Flashcards
What is arrhythmia?
Absence of rhythm
What is dysrhythmia?
Disturbance in rhythm
How are dysrhythmias classified?
Site of origin, effect and frequency of occurrence
What are the possible sites of origin of dysrhythmias?
Atrial
Ventricular
Junctional (supraventricular)
What is meant by a true dysrhythmia?
A very disorganised rhythm
What is meant by tachycardia?
Heart beat too fast
What is meant be bradycardia?
Heart beat too slow
What is paroxysmal supraventricular tachycardia?
Happens in attacks, rapid but regular heart beat
What are ectopic heartbeats?
Skipped or extra heartbeats leading to irregular heart rate and heart rhythm
What is multifocal atrial tachycardia?
electrical impulses arriving from multiple locations within atria
What is ventricular fibrillation?
Rapid heartbeat initiated within ventricles. It is characterised by 3 or more consecutive premature ventricular beats
What is the most common type of bradydysrhythmia?
Heart block - communication between atria and ventricles is disrupted
What is the difference between first, second and third degree heart block?
First: slowed conductance through AVN
Second: some atrial impulses fail to make it through to ventricles
Third: no conduction from atria to ventricles - complete heart block
What is asystolic arrest?
Complete cessation of electrical activity - bradydysrhythmia
What are the five main mechanisms that lead to dysrhythmia?
Ectopic pacemakers - conducting tissue other than SAN initiate heart beat
Delay after depol - build up on Ca2+ in cells leading to train of APs
Re-entry circuits - Tissue damage leads to AP travelling in circles
Congenital abnormalities - additional conducting pathways between atria and ventricles
Heart block - damage to conducting pathways disrupts signalling between atria and ventricles
Ectopic foci lead to an odd shaped ___ wave on ECG
P
Heart rate increase if rate of ectopic focus exceeds rate of SAN. True or false?
True
What takes place in AF that leads to abnormal impulse generation?
Atrial myocytes contract independently, each atria potentially acts as ectopic focus so there is no coordinated contraction of atria so QRS complex occurs at irregular intervals
Ventricular fibrillation can be a result of ectopic foci or re-entry circuits. True or false?
True
Ventricular fibrillation is a true arrhythmia. True or false?
True
In ventricular fibrillation, the ventricles are not coordinated in contraction and there is no ____ wave on ECG
QRS
What is Wolff-Parkinson-White syndrome?
A congenital abnormality where there are additional conducting pathways between the atria and ventricles known as Kent bundles.
Signals go via AVN and Kent bundles leading to atrial flutter - ventricles try to keep up pace with atria - sudden death possible
Kent bundles can also set up re-entry circuits
Can Kent bundles be surgically removed?
Yes - if one or two present usually surgically removed
All dysrhytmias are abnormal and dangerous. True or false?
False - sinus dysrhythmia is an alteration of HR brought about by breathing - particularly common in young people
What is the VW system?
main classification system used for anti-dysrhythmic drugs
In the VW system, which receptors are targeted in the different classes?
Class I - Na channels Class 2 - B1 receptor Class 3 - K channel Class 4 - Calcium channel Unclassified - various
What are the main drugs in the classes of VW system?
Class I - Lidocaine
Class 2 - Atenolol
Class 3 - Amioderone
Class 4 - Verapamil
Which class of the VW system is further subdivided into a, b and c?
Class 1
How do class 1 drugs in the VW system work?
They block sodium channels in a use-dependence manner (preferentially block open and inactivated channels). They share this mechanism with local anaesthetics
Which class does lidocaine belong to and how is it administered?
Class 1b - IV because metabolised by the liver so not given orally
What is lidocaine’s clinical use?
Ventricular dysrhythmia
What class do procainamide and disopyramide belong to?
1a
What class does flecainide belong to?
1c
Class 1c drugs are useful in preventing paroxysmal atrial fibrillation. True or false?
True
Class 1c drugs should be used after heart attacks. True or false?
False - avoid after heart attacks - sudden death likely
B1 antagonists are particularly useful if sympathetic nervous system is involved in dysrhythmia. True or false?
True
B1 blockers are useful for supraventricular and ventricular disrhythmia. True or false?
True
What are the unwanted side effects of beta blockers?
Bronchoconstriction Heart block Hypoglycaemia Cold extremities Vivid dreams
What is one of the weaknesses of VW system?
Some drugs act by more than one mechanism
How does amiodarone work?
By blocking potassium channels (also blocks sodium and calcium)
What is amiodarone useful for treating?
Supraventricular, ventricular dysrhythmias and WPW syndrome, AF
How do potassium channel blockers work in reducing heart rate?
Potassium channel activation contributes to repolarisation so by blocking the channels, action potentials are prolonged and so is the refractory period therefore there is a decrease in heart rate
Which drug is an analogue of the thyroid hormone?
Amioderone
Amioderone is very lipophilic. True or false?
True
What are the ways in which amioderone is administered?
Orally or IV into a central vein
Although amioderone reduces heart rate, it alters the force of contraction, which isn’t good. True or false?
False - doesn’t alter the force of contraction
What does cardiac rhythm depend on?
Ion channel activity and calcium ion concentration
What is the structure of calcium channels (and sodium channels)?
Large proteins formed from an alpha subunit and a beta subunit. The alpha subunit consists of 4 pseudo-subunits.
The pseudo-subunits have 6 transmembrane domains with a membrane dipping domain between the 5th and 6th transmembranes.
The 4th transmembrane is charged and acts as a voltage sensor
Voltage gated channels can exist in three states. What are they?
Resting
Open
Inactivated
What is verapamil used for?
Prophylactically for paroxysmal supraventricular tachycardia and also in patients with AF to decrease ventricular rate
Is Verpamil safe to use for patients with WPW?
No - dangerous
Class IV drugs act on which type of calcium channel?
L-type
What are unwanted side effects of amiodarone?
Thyrotoxicosis
Hepatoxicity
Bradycardia
Micro-crystals in the cornea
What are the major side effects of verapamil?
AVN block
Reduction in CO
Which drug has a mechanism of reducing after-depolarisations?
Verapamil
What causes after-depolarisations to take place?
Build up of calcium in cell due to repeated stimulation which triggers chain of APs
Ziconotide is a drug that blocks which type of calcium channel?
N-type
What are weaknesses of VW system?
Excludes some potential sites for antidysrhythmic drugs
Doesn’t allow for the fact that some drugs have multiple mechanisms of action
Does not all for the fact that drug action on diseased tissue may differ from that on healthy tissue
What is digoxin used for?
Heart failure
Antidysrhytmic effects of digoxin are largely mediated by which nerve?
Vagus
Ziconotide requires intrathecal delivery. True or false?
True
Ziconotide has a narrow therapeutic window. True or false?
True
How does digoxin work?
It increases vagus nerve activity which:
reduces SAN firing rate
reduces AVN conduction velocity
reduces ventricular rate
Digoxin has a narrow therapeutic index. What happens if it is given at a toxic dose?
Increases sympathetic tone - dysrhythmia -
depolarisation
increases afterdepolarisations
increases ectopic beats
How is digoxin toxicity treated?
Stop digoxin administration
Correct hypokalaemia by giving KCl orally/infusion
Give propranolol/phenytoin
How does adenosine work?
Activation of adenosine leads to activation of K+ channels and so hyperpolarisation, reducing AP duration and inhibiting Ca2+ channels.
What can adenosine be used for?
Supression of:
Supraventricular tach
Ventricular tach - WPW
PSVT
Why can’t adenosine be used chronically?
Because it’s plasma half life is 10s
