Arrhythmia drugs Flashcards
Which class of drugs do procainamide and quinidine belong to?
Class 1a
What is the mode of action of class 1a drugs such as procainamide and quinidine? (3)
Moderate sodium channel blockers- slow depolarisation, slow conduction velocity and prolong repolarisation.
What class of drugs to propanolol, bisoprolol, atenolol and metoprolol belong to?
Class 2
Describe the mode of action of class 2 antiarrhythmics such as propanolol (3)
They are beta blockers- slows depolarisation and slow funny currents of SAN to slow HR, they also increase refractory period at AVN.
Name one class 1c antiarrhythmic.
Flecainide
What is the mode of action of class 1b drugs like lidocaine?
Class 1b dissociate from the sodium channels very quickly, so have no effect on sodium channels in normal tissue, but in ischaemic/ depolarised tissue they’ll inactivate the open sodium channels and repolarise the tissue.
What is the difference between mode of action of class 1 a and c drugs?
Class 1c drugs dissociate from the sodium channels more slowly so cause more marked increase in threshold and decreases in conduction velocity.
Give 2 examples of a class 3 anti- arrhythmic
amiodarone
How does amiodarone work?
Block K+ channels- alone this extends refractory period to slow conduction and terminate arrythmias, but may lead to early after depolarisations. For this reason it also has some Class 1, 2 and 4 actions as well
How does sotalol work?
Blocks K+ channels and is also has some beta- blocker properties
What class of drugs does verapamil and amlodopine belong to?
class IV
Other than verapamil and amlodipine, name one other class IV anti- arrhythmic?
Dilitazem
How do class IV anti- arrhythmics such as dilitazem and verapamil work?
Blocks Ca2+ channels- mainly in the AVN, to slow conduction and increase refractory period and increase the threshold for conduction.
How does adenosine work?
Binds to A1 receptors, activating K+ channels in SAN and AVN, causing hyperpolarisation and so a drop in HR, it also binds to Ca2+ channels in the AVN, increasing the refractory period.
How does vernakalent work?
Blocks K+ channels in the atria only- slowing atrial conduction, so helping to terminate atrial fibrillation
How does ivrabradine work?
Blocks HCN/ funny current channels in the SAN. This slows HR, but doesn’t affect contractility or work systemically so maintains BP- unlike B- blockers.
How does digoxin work? (2)
It is a cardiac glycoside, so increases vagal activity- increase k+ conduction, decrease Ca2+ channels and increase refractory period in AVN to slow HR.
It also inhibits Na/K/atpase so Na+ builds up, NCX swaps and Ca2+ enters, which increase contractility- thus maintaining good CO even though HR drop.
How does atropine work?
Muscarinic antagonist, so increases HR.
What effect do Class 1a drugs have on an ECG?
Wider QRS complex (slows action potentials) and longer QT interval (slower conduction velocity)
When are class 1a drugs procainamide and quinidine used?
Procainamide: Supraventricular and ventricular tachycardic arrhythmias.
Quinidine: AF and atrial flutter.
Both are broad spectrum
List 3 side effects of class 1a antiarrhythmics
- Hypotension- less contractility and slower HR
- pro-arrythmic as they prolong QT
- GI upset
- Dizziness, confusion, seizure, insomnia at high dose
What effect do class 1b anti- arrhythmic have on an ECG?
No effect in normal tissue, widens QRS complex in ischeamic or fast beating tissue
When are class 1b antiarrhythmics used?
In ventricular tachycardia due to MI/ angina
Give 3 side effects of class 1b anti- arrhythmics?
Dizziness, drowsniess, GI upset
No effect on normal tissue to no hypotension etc.
What effect do class 1c anti- arrhythmics have on an ECG?
increase PR interval- slower conduction, widen QRS and QT interval due to slower conduction
When are class 1c anti arrhythmics used?
Wide spectrum- supraventricular arrhythmias, WPW syndrome
Give 3 side effects of class 1c antiarrhymics?
- Quite proarrhythmic due to elongation QT, so dont use in structural heart disease or long term
- CNS and GI effects
Why should flecainide not be used on its own to treat AF?
It may decrease the rate of AF to a level where ventricles keep up, but rate is still 200+ so leads to ventricular tachycardia.
What effect to class 2 antiarrhythmics have on ECG?
increased PR interval (slows conduction from A-> V), slows HR (as slows rate of SAN depolarisation)
What arrhythmias are class 2 drugs such as bisoprolol, atenolol and propranolol used for?
supreventricular tachycardia, sinus tachycardia, terminating AV nodal reentry.
List 3 side effects for betablockers?
- Bronchoconstriction (dont use in asthmatics)
- hypotension (dont use in heart failure)
- slows AV conduction (so dont use in heart block)
What effect to class 3 antiarrhythmics like amiodarone have on ECG?
Extend PR, QRS and QT interval, decrease heart rate.
How does sotalol work?
Beta blocker but also has some K+ channel blocking properties, so increases QT interval and decreases heart rate
When can amiodarone be used?
wide spectrum- supra and ventricular tachycardias
List 4 side effects of amiodarone?
- pulmonary fibrosis
- hepatic injury
- thyroid disease
- photosensitivity
- increased LDL
The risk of theses increase w/ time so avoid long term use and if you do, use low dose + digoxin.
What effects do class 4 drugs like verapamil and dilitazem have on an ECG?
Increase PR interval (prolong time to get from SAN–> AVN), HR change variable depending on response to BP drop.
List 3 side effects of Calcium channel blockers
hypotension (avoid in heart failure), sick sinus syndrome, GI upset
What effects does adenosine have on an ECG?
increases PR interval (decreases AVN conduction) and decrease HR
When is adenosine used?
Atrial flutter, AVN reentry–> used in stable, regular, monomorphic wide complex tachycardia.
List 3 side effects of adenosine?
flushings, dyspnoea, headache, GI upset, AV block
When is digoxin used?
adjunct to reduce ventricualr rate in AF, esp if pt has heart failure as keeps contractility high while decreasing HR so maintaining cardiac output
List 2 side effects of digoxin?
dizziness, diarrhoea, nausea, headache
Describe the rate and rhythm control used in AF
Rate: B blocker (bisoprolol), Ca blocker (verapamil) +/- digoxin
Rhythm: K+ blocker (amiodarone), Na+ blocker (flecainide), vernakalent
Rate control is 1st line, rhythm only used in acute episodes usually.
Describe acute treatment of re- entrant SVT
Adenosine (slows rate), flecainide (may terminate), verapamil (slows rate).
Chronic is same - adenosine + B blocker/ sotalol
Describe treatment of ectopic beats
beta blockers - bisoprolol first, then Na+ blockers (flecainide)
Describe treatment of wolf- parkinson- white syndrome
- flecainide to slow conduction back to atria
- Amiodarone to slow conduction further, back to paceset by SAN
