Pharmacological Management of Dysrhythmia Flashcards
1
Q
What are dysrhythmias and what causes them?
A
- Dysrhythmia describes conditions where the coordinated sequence of electrical activity in the heart is disrupted.
- Can be due to:
- Changes in the heart cells
- Changes in the conduction of the impulse through the heart.
- Combination of these.
2
Q
Describe the Vaughan Williams system of classifying anti-dysrhythmic drugs.
A
- Sodium channel blockers (divided into 1a, 1b, 1c).
- β-adrenoceptor blockers.
- Potassium channel blockers.
- Calcium channel blockers.
- Unclassified.
3
Q
How do sodium channel blockers work?
A
- They inhibit action potential propagation and reduce the rate of cardiac depolarisation during phase 0.
- They bind to the open and refractory states of the channels and so are viewed as use-dependent.
- This means that they work more efficiently if there is high activity and so are more effective against abnormal high frequency activity and not so much against normal beating rates.
- They can block from the cytoplasmic side or the luminal side.
4
Q
What is Disopyramide and what are the indications for its use?
A
- Disopyramide is a class 1a sodium channel blocker.
- Indications for use:
- Ventricular and supraventricular dysrhythmia.
- Prevention of recurrent atrial fibrillation triggered by vagal over-activity.
- Maintenance of sinus rhythm after cardioversion.
5
Q
What is Lignocaine and what are the indications for its use?
A
- Lignocaine is a class 1b sodium channel blocker.
- Indication for use:
- Treatment and prevention of ventricular tachycardia and fibrillation during and immediately after MI.
- To be given during CPR as an alternative if amiodarone is not available.
6
Q
What is Flecainide and what are the indications for its use?
A
- Flecainide is a class 1c sodium channel blocker.
- Indications for use:
- Suppresses ventricular ectopic beats.
- Prevents paroxysmal atrial fibrillation and recurrent tachycardia associated with abnormal conducting pathways.
7
Q
What are the contraindications of Disopyramide (class 1a sodium channel blocker)?
A
- Bundle branch block associated with first-degree AV block.
- Second- and third- degree AV block (unless pacemaker fitted).
- Severe heart failure (unless secondary to arrhythmia).
- Severe sinus node dysfunction.
8
Q
What are the contraindications of Lignocaine?
A
- All grades of AV block.
- Severe myocardial depression.
- Sinoatrial disorders.
9
Q
How do β-Adrenoceptor blockers work?
A
- Block β-1 receptors, slowing the heart rate and decreasing cardiac output.
- β-1 receptor activation increases the rate of depolarisation of th pacemaker cells, so blocking them decreases this.
- β-1 receptor activation enhances calcium entry in phase 2 of the cardiac action potential, so blocking them reduces this.
- β-blockers increase the refractory period of the AV node, so prevent recurrent attacks of supraventricular tachycardias.
- Basically increased sympathetic drive and influence tend to promote dysrhythmias and so attenuating their influence will slow the heart and decrease their occurrence.
10
Q
Give examples of β-blockers.
What are the indications for their use?
A
- Sotalol, bisopralol, atenolol.
- Indications for use:
- Reduce mortality following MI
- Prevent recurrence of tachycardias provoked by increased sympathetic activity.
- Also used in hypertension, angina, arrhythmias, heart failure and thyrotoxicosis.
11
Q
What are the contraindications for β-blocker use?
A
- Symptomatic bradycardia
- AV block
- Decompensated heart failure
- Asthma
12
Q
What are the common adverse effects of β-blockers?
A
- Nausea, weakness and dizziness.
- Cold hands and feet.
- Fatigue.
- Slow heart rate.
- Swelling of hands and feet.
13
Q
How do potassium channel blockers work?
Give an example of a potassium channel blocker.
A
- They prolong the cardiac action potential by prolnging the refractory period.
- Amiodarone
14
Q
What are the indications for use of a potassium channel blocker?
A
- Amiodarone is used to treat tachycardia associated with Wolff-Parkinson_white syndrome.
- Sotalol combines class 3 with class 2 actions. It is used in supraventricular dysrhythmias and suppress ventricular ectopic beats and short runs of tachycardia.
15
Q
What is Wolff-Parkinson-White Syndrome?
A
- Wolff-Parkinson-White syndrome is a heart condition featuring episodes of an abnormally fast heart rate.
- Episodes can last for seconds, minutes, hours, or (in rare cases) days.
- They may occur regularly, once or twice a week, or just once in a while.
- The combination of Wolff-Parkinson_white syndrome and atrial fibrillation can be life-threatening.
18
Q
How do calcium channel blockers work?
Give an example of a calcium channel blocker.
A
- Blocks cardiac voltage-gated L-type calcium channels.
- Slow conduction through the SA and AV nodes where the conduction of the action potential relies on the slow calcium currents.
- They shorten the plateau of the cardiac action potential and reduce the force of contraction of the heart.
- Verapamil is the main drug.
