Pharmacological Treatment of Dysrhythmias Flashcards
What is a long QT interval (>0.4 - 0.44) caused by?
A mutation in K+ channels
What phases are not included in the SA node?
Phase 1 and 2
How are dysrhythmias classifiedin terms of where the abnormality arises?
- Atrial (supraventricular)
- Junctional (assciated with AV node)
- Ventricular
What are the 1a class of antidysrhythmic drugs (Vaughan Williams) system?
Sodium channel blockers e.g disopyramide
What are the 1b class of antidysrhythmic drugs (Vaughan Williams) system?
Sodium channel blockers e.g lignocaine
What are the 1c class of antidysrhythmic drugs (Vaughan Williams) system?
Sodium channel blockers e.g flecainide
What are the 2 class of antidysrhythmic drugs (Vaughan Williams) system?
b-adrenoreceptor blockers e.g sotalol
What are the 3 class of antidysrhythmic drugs (Vaughan Williams) system?
Potassium channel block e.g amiodarone
What are the 4 class of antidysrhythmic drugs (Vaughan Williams) system?
Calcium channel blockers e.g verapamil
Name 2 unclassified antidysrhythmic drugs
Adenosine and digoxin
How do the class1 dysrhtmic drugs operate?
- They inhibit the action potential and they reduce the rate of cardiac depolarisation during phase 0
- Use-dependant
What is the clinical use of class 1a antidysrhtmics (disopyramide)?
- Ventricular dysrhythmias, prevention of recurrent atrial fibrilation triggered by vagal over-activity.
What is the clinical use of class 1b antidysrhythmics (lignocaine)?
Treatment and prevention of ventricular tachycardia and fibrilation during and immediately after MI
What is the clinical use of class 1c antidysrhythmics (Flecainide)?
Suppresses ventricular ectopic beats. Prevents paroxysmal atrial fibrilation and recurrent tchycardias associated with abnormal conducting pathways.
How do class 2 antidysrhythmics work?
- They block Beta 1 receptors
- B1 receptors enhance calcium entry in phase 2 of the cardiac action potential so blocking them reduces this
- Beta blockers increase the refractory period of the AV node so prevent recurrent attacks of supraventricular tachycardias
- Slowing HR by blocking SA node will decrease occurence of dysrhythmias
What drug can be considered a class 2 and 3 antidysrhythmic?
sotalol
How do class 3 drugs (amiodarone) work?
- They are potassium channel blockers
- They prolong the cardiac action potential by prolonging the refractory period
What drug is WPW syndrome treated with?
Amiodarone (class 3) (K+ channel blocker) Also effective in many other supraventricular and ventricular tachyarrhythmias
`What conditions are treated with Sotalol?
It is used in supraventricular dysrhythmias and suppresses ventricular ectopic beats and short runs of ventricular tachycardia
How do class 4 antidysrhythmics work?
- Blocks cardiac voltage-gated L-type calcium channels
- Slow conduction through SA and AV nodes where the conduction of the AP relies on the slow calcium currents
- They shorten the plateau of the cardiac AP and reduce the force of contraction of the heart
How does adenosine work?
- A1 receptor is responsible for thr effect on the AV node
- These receptors are linked to the same cardiac potassium channels that are activated by ACh. and so it hyperpolarises cardiac conducting tissue and slows the HR. It decreases pacemaker activity
- Used to terminate SVTs
How does digoxin work?
- Increase vagal efferent activity to the heart
- The parasympathomimetic action of digoxin reduces SA firing rate (decreasing HR) and reduces conduction velocity of electrical impulses through the AV node
- Toxic concentrations disturb sinus rhythm. Inhibition of Na/K+ pump cause depolarisation - ectopic beats
