PHARM - Drugs for the Treatment of Heart Failure and Arrhythmia - Week 5 Flashcards
Which nodes of the heart does parasympathetic innervation target (2), what neurotransmitter and what receptor? What effect does it have on heart rate?
Both the sino-atrial and atrio-ventricular nodes.
It uses acetylcholine and targets muscarinic M2 receptors.
Decreases heart rate.
Which nodes of the heart does sympathetic innervation target, what neurotransmitter and what receptor? What two effect does it have on the heart?
Targets the SA node.
Uses noradrenaline and targets B1 adrenoceptors.
Increases heart rate and contractility.
Compare the SA and the ventricle in terms of their membrane stability. Comment how this affects depolarisation.
SA node - unstable membrane, spontaneous depolarisation.
Ventricle - stable membrane, rapid depolarisation
Name the four major classes of drugs used to control heart rate, according to the Vaughan Williams classification.
Class 1 - Na+ channel blocker
Class 2 - B-adrenoceptor antagonism
Class 3 - K+ channel blocker
Class 4 - Ca2+ channel blocker
Explain why it is sometimes important to consider giving no treatment for arrythmia.
Many antiarrhythmics have proarrhythmic activity and may worsen arrhythmias and cause sudden death.
What effect do Na+ channel blockers have on ventricular depolarisation?
Reduces rate
In what state is a Na+ channel when a blocker binds it? What is this called?
Open state - use dependent channel block
How many subclasses of Class 1 Na+ channel blockers are there, and how are they classified?
Class 1a, 1b, and 1c
They are classified based on dissociation time of the drug from the channel
When are class 1b Na+ channel blockers typically used (3)? Give an example of a major drug in this category.
Lignocaine (lidocaine)
Used post myocardial infarction, in ventricular dysrrhythmias, and fibrillation
What action do K+ channel inhibitors have on the heart (mechanistically)?
Prolongs ventricular action potentials
Name 3 unclassified agents for treating arrhythmias.
Atropine
Adenosine
Digoxin
What effect does digoxin have on the heart (4)?
Slows AV conduction, increasing vagal input to the heart.
Slows ventricular rate, and improves filling.
What condition may digoxin cause?
Ventricular fibrillation
Does digoxin have a high or low therapeutic index?
Low
Name 4 symptoms that digoxin can relieve. Does it increase or decrease cardiac output?
Increases cardiac output and relieves: Fatigue Oedema Shortness of breath Palpitations
