Anti-arrhythmics Flashcards
What is the distribution of ions inside and outside a cardiac myocyte?
Na higher outside
Ca higher outside
K higher inside
What are the diff ends phases of the cardiac action potential?
Phase 0 - depolarisation, Na influx
Phase 1 - slight repolarisarion, K+ and Cl- out
Phase 2 - plateau - Ca in, K out
Phase 3 - repolarisarion - K out
Phase 4 - resting membrane potential
Why arrhythmias cause the heart to contract too quickly?
AF
AV re-entry tachycardia
Ventricular tachycardia
Torsades de Pointes
What arrhythmias can cause the heart to be too slow?
Sinus bradycardia
First to third degree heart block
What can cause cardiac arrhythmias (at more of a cellular level, not clinical conditions)
Enhanced automaticity
Delayed after-depolarisations
Early after-depolarisations
Re-entry circuits
What are class I anti-arrhythmic drugs?
Sodium channel blockers
What are class II anti-arrhythmic drugs?
Beta blockers
What are class III anti-arrhythmic drugs?
Potassium channel blockers
What are class IV anti-arrhythmic drugs?
Calcium channel blockers
What is the path of the action potential in the heart?
SA node Across atria AV node Bundle of His Left and right bundle branches
Difference between class Ia, b and c drugs?
1a - intermediate dissociation
1b - rapid dissociation
1c - slow dissociation
Give an example of class 1a
Quinidine
Procainamide
What is the effect of 1a drugs?
Slow phase 0 of action potential in ventricular muscle fibres
Increase the refractory period/repolarisation
Decrease automaticity
Increase the threshold
What is automaticity?
A cell’s ability to spontaneously generate an electrical impulse
What changes are seen on an ECG with 1a drugs?
Increase QRS
Increase PR interval
Increase QT interval
Uses of 1a drugs?
Quinidine - maintains a sinus rhythm in AF and flutter, prevents recurrent tachycardia and fibrillation
Procainamide - used for acute treatment of supraventricular and ventricular arrhythmias
ADRs of 1a drugs?
Hypotension Reduced CO Pro-arrhythmia eg Torsades de Pointes GI effects Dizziness, confusion, insomnia, seizure Lupus-like syndrome
How do 1b drugs work?
Bind to inactive sodium channels in phase 0 and dissociate rapidly in time for next action potential
Stop a premature beat because the sodium channels would still be blocked but have no effect in normal tissue
Increase the threshold for action potential
Use-dependent
Effects on ECG of class 1b?
None in normal tissue
Increase QRS complex in fast-beating or ischaemic (depolarised) tissue
Name some class 1b drugs
Lidocaine
Mexilatine
Phenytoin
Uses of class 1b?
Prevent ventricular tachycardia and fibrillation following an MI
(IV lidocaine given)
ADRs of 1b? (Lidocaine)
Less pro-arrhythmic than 1a due to less effect on QT
CNS - drowsiness and dizziness
How do class 1c drugs work?
Slow dissociation with sodium channels so reach a steady state of block
Decreases automaticity and increases threshold
Increases action potential duration and increases refractory period
Decreases phase 0 in normal tissue
Effects of 1c on ECG?
Increase PR
Increase QRS
Increase QT
Uses of 1c?
Supraventricular arrhythmias (fibrillation and flutter)
Premature ventricular contractions
Wolff-Parkinson-White syndrome
Side effects of 1c?
Pro-arrhythmic - sudden death especially in chronic use
Increased ventricular response to supraventricular arrhythmias
CNS and GI effects
Name some class 1c drugs
Flecainide
Propafenone
Effect of beta blockers on the heart?
Diminish phase 4 depolarisation (catecholamine depenedent), therefore
- depresses automaticity
- prolongs AV conduction
- decreases heart rate and contractility
Slows AV node conduction velocity
Effects on ECG of beta blockers?
Increased PR (slowed AV node conduction) Decreased heart rate
Uses of beta blockers as anti-arrhythmics?
Treat sinus and catecholamine-dependent tachycardia and arrhythmias caused by increased sympathetic activity (eg after MI)
Protect ventricles from AF and flutter by slowing AV conduction
Convert re-entrant arrhythmias in AV which can cause tachycardias
ADRs of beta blockers?
Bronchospasm
Hypotension
Contra-indications of beta blockers?
Partial AV block
Ventricular failure
Asthma
Overall effect of potassium channel blockers?
Prolong the action potential duration without altering phase 0, just lengthen the plateau (phase 3) as there is less efflux of potassium
Name some potassium channel blockers
Amiodarone
Sotalol
Administration of amiodarone?
Orally or IV
Loading dose required due to the long half-life of three months
Cardiac effects of amiodarone?
Increase the refractory period and action potential duration
Increase the threshold
Decrease phase 4
Increase speed of AV node conduction
Effects on the ECG of potassium channel blockers?
Increased PR
Increased QRS
increased QT interval
Decreased heart rate
Uses of potassium channel blockers?
Wide spectrum - most arrhythmias
Especially AF
ADRs of amiodarone?
Pulmonary fibrosis Hepatic injury (reversible) Increased LDL cholesterol Thyroid disease Photosensitivity
Cardiac effects of sotalol?
Increases action potential duration
Slows phase 4 (beta blocker)
Slows AV conduction
Effects on ECG of sotalol?
Increases PR
Decreases heart rate
Uses of sotalol?
Supraventricular and ventricular tachycardias
ADRs of sotalol?
Pro-arrhythmia - long QT interval - Torsades de Pointes
Fatigue
Insomnia
Uses of amiodarone?
Tachycardia associated with Wolff-Parkinson-White syndrome
Many other supraventricular and ventricular tachycardias
Examples of calcium channel blockers and how they are administered?
Verapamil - oral or IV
Dilitiazem - oral
Cardiac effects of calcium channel blockers?
Slows conduction though AV
Increased refractory period in AV node
Decreased rate of phase 4 spontaneous depolarisation
Increased PR
Increased or decreased heart rate depending on blood pressure response and baroreceptor reflex
Effect of calcium channel blockers on the ECG?
Uses of calcium channel blockers?
Control ventricles in supraventricular tachycardia eg AF
Treat re-entrant supraventricular tachycardia around AV node
More effective against atrial arrhythmias
Hypertension and angina
ADRs of calcium channel blockers?
Caution when AV block is present - can get a systole with a beta-blocker
Caution in hypotension - can get decreased cardiac output or sick sinus
GI
Which calcium channel blockers have the greatest effect on heart muscle, vascular smooth muscle and which are in between?
Heart muscle - verapamil
Nifedipine - vascular smooth muscle
Dilitiazem - intermediate
Administration and half-life of adenosine?
Rapid IV bolus
Half-life = seconds
Mechanism of action of adenosine?
A nucleoside which binds to A1 receptors and activates adenylyl cyclase
Causes efflux of potassium, hyperpolarising the membrane
Therefore decreases conduction velocity, prolongs the refractory period and decreases automaticity in the AV node
Uses of adenosine?
Terminates (re-entrant) supraventricular tachycardias
Hypotension during surgery
Diagnosis of CAD
Side effects of adenosine?
Flushing
Chest pain
Hypotension
Mechanism of action of digoxin?
Inhibits Na-K-ATPase on cardiac myocytes
Causes increased intracellular Na concentration
Slows the Na/Ca exchange which pumps calcium out, sodium in
More calcium inside the cell, so more is stored in the SR
More calcium released in an action potential, causing increased muscle contraction of the heart
Overall effects of digoxin?
Increases force of cardiac contraction (positive inotrope)
Enhances vagal activity
Slows AV conduction and heart rate
Uses of digoxin/cardiac glycosides?
Atrial fibrillation and flutter
Mechanism of action of atropine?
Causes tachycardia by blocking muscarinic receptors, inhibiting effect of parasympathetic nervous system
Effects of atropine on the heart?
Blocks vagal activity causing an increase in AV node conduction speed and increases heart rate
Uses of atropine?
Vagal bradycardia
Uses of magnesium?
Treats tachycardia resulting from long QT
Which drugs can be used for supraventricular arrhythmias?
Adenosine
Verapamil
Cardiac glycosides
Beta blockers
Which drugs can be used for supraventricular and ventricular arrhythmias?
Amiodarone
Beta blockers
Flecainide
Propafenone
Which drugs can be for ventricular arrhythmias?
Lidocaine
Moacizine
