Treatment and Pharmacology of Arrhythmias Flashcards
What are the 5 treatment options for AF/other supraventricular tachycardias?
1) Anti-arrhythmic drugs
2) Radiocatheter ablation
3) Maze procedure
4) Anti-coagulants
5) LA appendage closure
How many classes of anti-arrhythmic drugs are there?
4
What are class 1 anti-arrhythmic drugs?
Sodium channel blockers
What do class 1 anti-arrhythmic drugs do?
Suppress conduction
What is an example of a class 1 anti-arrhythmic drug?
Flecainide
What are class 2 anti-arrhythmic drugs?
Beta receptor blockers
What do class 2 anti-arrhythmic drugs do?
Reduce excitability and inhibit AVN conduction (by suppressing noradrenaline-mediated stimulation of AVN conduction) → prevents some f waves stimulating ventricular depolarisation and contraction
What is an example of a class 2 anti-arrhythmic drug?
Bisoprolol
What do class 3 anti-arrhythmic drugs do?
Prolong the AP and refractory period
What is an example of a class 3 anti-arrhythmic drug?
Amiodarone
What are class 4 anti-arrhythmic drugs?
Calcium channel blockers
What do class 4 anti-arrhythmic drugs do?
Inhibit AVN conduction (bc the action potential in the AVN is mediated by calcium, not sodium)
What is an example of a class 4 anti-arrhythmic drug?
Verapamil
What are the other two anti-arrhythmic drugs that don’t fit into the classes?
Adenosine and digoxin
How does adenosine work?
Slows AVN conduction (rapidly acting injection so can stop AF quickly) by inhibiting AVN calcium channels and stimulating potassium channels
How does digoxin work?
Stimulates the vagus, slowing/suppressing AVN conduction (vagus innervates AVN)
What do all anti-arrhythmic drugs do?
Inhibit conduction or reduce excitability in some way
What are the two types of anti-arrhythmic drugs?
Rate control or rhythm control
How do rate control anti-arrhythmic drugs work?
- Reduce the proportion of impulses conducted through the AVN
- Atrial tachycardia continues, but the ventricles slow down, improving CO
What do rhythm control anti-arrhythmic drugs do?
Target the source of the arrhythmia or the conduction of the impulse away from the source by blocking the re-entrant pathway
Which drugs are rate control drugs and why?
- Class 2, class 4, adenosine(?) and digoxin (BCD)
- All these drugs reduce the ability of the AVN to conduct impulse from the atria to ventricles
Which drugs are rhythm control drugs and why?
- Class 1 and 3 (and adenosine??) (NaAA)
- These drugs suppress re-entry (as described in flashcard how to stop re-entry)
Why is anti-coagulant therapy required in AF?
To prevent stroke
How are the two types of anti-arrhythmic drugs used?
Rate control may be tried first, but often both approaches are used together
How do rate control drugs work (more detail)?
1) In AF, the AVN is being bombarded with chaotic waves of atrial depolarisation
2) Most of these are too small to be conduced, but some are which lead to rapid irregular ventricular depolarisation and pumping
3) Rate control aims to reduce the % of these waves which are conduced through the AVN
4) This decreases the frequency of ventricular depolarisation
5) Therefore the ventricles have more time to fill, so CO decreases
What happens in radiofrequency catheter ablation?
1) The ectopic pacemaker or site along a re-entrant pathway is destroyed
2) A transvenous catheter is threaded into the heart, placed against the endocardium, and radiofrequency energy is delivered to the top
3) This heats the top causing a lesion ~1cm wide → this scar intervenes in the re-entrant pathway
Describe cryoablation
- Newer alternative to radiofrequency catheter ablation
- It is used if the site to be ablated is v close to the AVN or conduction system
- Also causes a scar in the ectopic site
Describe the effectiveness of ablation
- Relatively safe
- Widely used for SV tachycardias
- Success rate ~75% for AF, and higher for other types of SV arrhythmias
- Increasing use for VT but more difficult and less often effective
What are the 3 treatment options for VT (chronic ventricular arrhythmias)?
1) Implanted cardioverter defibrillator (AVID trial)
2) Class 1,2 and 3 anti-arrhythmic drugs
3) Radiocatheter ablation (can be effective in some patients)
What are the two aims of pharmacological treatment for VT and which drugs carry out each aim?
1) Inhibit conduction in the conduction system or cardiac muscle or increase the refractory period → Class 1 or 3
2) Reduce excitability → Class 2
What does rhythm control do?
Block re-entry
Why are class 3 anti-arrhythmic drugs do in VT?
- Prolong the refractory period, leading to refractory myocardium (still with slowed conduction)
- When the impulse comes t
through, the myocardium so still refractory so the impulse dies out
How effective are class 1 and class 3 drugs for VT?
Not very
Why are class 1 anti-arrhythmic drugs do in VT?
Suppress conduction, leading to blocked conduction (with non-refractory myocardium)
What is the myocardium and conduction like in VT?
Non-refractory myocardium and slowed conduction
How is an implantable defibrillator set up?
An implanted generator is connected to electrodes in the right ventricle and the superior vena cava
How does an implantable defibrillator work?
The generator can sense and differentiate arrhythmias by rate and location and then deliver an appropriate shock or shock sequence, causing cardioversion
What is cardioversion?
A return to sinus rhythm
Why might implantable defibrillators sometimes be combined with drugs?
To reduce frequency of fibrillation episodes bc receiving shock can be stressful for patients
What drug may be combined with an implantable defibrillator?
Amiodarone
What treatment is more successful than drug therapy in patients with serious ventricular arrhythmias?
Implantable defibrillators
What is used to terminate VF or ‘pulseless’ VT?
Defibrillation
What is DC cardioversion?
Momentary discharge of large current across the chest via paddles placed at the sternum and PV apex
What is defibrillation applied?
At the onset of the QRS complex (if present)
How does defibrillation work?
It stops the heart, allowing the SAN to reassert itself
What drug can be used in combination with CPR (and defibrillation?)
Adrenaline
In the absence of any equipment, what can occasionally terminate VF?
A thump to the chest
How is 3rd degree heart block treated?
- Implantation of a permanent pacemaker to generate the cardiac rhythm (unless risk is low or block is likely to be temporary)
- If risk of asystole is high, may need immediate temporary pacemaker as well
What happens in a cardiac event e.g. AF?
More NA is released by cardiac nerves
