Bradyarrhythmia and inotropy pharmacology Flashcards
What is AV block?
Interruption of impulse from atria to ventricles
What is sick synus syndrome?
Dysfunctional SAN
What is atrial standstill?
Failure of atrial depolarisation - temporary/permanent lack of atrial activity
What is a problem with all CV pharmacology?
Combination of problems and side effects - patients rarely have one condition
Are bradyarrhythmias more or less common than tachyarrhythmias? What may bradyarrhythmias require?
Less common
Pacemaker
How does the body physiologically increase heart rate? Why is this a problem for bradyarrhythmic pharmacology?
Increased sympathetic nervous system activity Pathway broken (unlike in tachycardia)
What are the 4 categories of positive chronotropes used to treat bradyarrhythmias?
Sympathomimetics
Anticholinergics
Methylxanthine
PDE III inhibitors
How do methylxanthines work?
Reduce hyperpolarisation of cell through potassium channels
Give an example of a methylxanthine?
Theophylline
What does PDE do? What is PDE III?
Degrade intracellular cAMP
Heart specific PDE
What happens if PDE is inhibited?
Increased intracellular cAMP
Activates protein kinase
Phosphorylates calcium
Stronger contractions
Give an example of a PDE III inhibitor
Pimobendan
What are the 2 types of sympathomimetics? Give an example of each
B1 agonists - dobutamine
B2 agonists - terbutaline
What effects do B1 agonists have?
Positive chronotropy
Positive inotropy
What effects do B2 agonists have?
Positive chronotropy
Positive dromotropy
What effect do anticholinergics have? What can they be used for?
Positive chronotrope
Positive dromotrope
Short term anaesthesia
Give an example of an anitcholinergic
Atropine
What are the 3 categories of positive inotropes?
Sympathomimetics
PDE III inhibitors
Cardiac glycosides
(Anticholinergics, glucagon)
How do positive inotropes generally cause increased contractility?
Mimic/enhance sympathetic activity
Increase intracellular Ca2+
Increases EDVV
PDE III inhibitors are positive chronotropes and inotropes. What other effects do they cause?
Vasodilation
Faster depolarisation
How do PDE III inhibitors cause vasodilation?
Increased intracellular cAMP
Dephosphorylates MLCK
Smooth muscle relaxation
What effects does pimobendan have?
Positive inotrope
Vasodilator
How is pimobendan administered? Where is it metabolised/activated and excreted?
Oral or parenteral
Activated in liver
Excreted in faeces
What are the side effects of pimobendan?
Inappetance
Lethargy
Dyspnoea
Azotaemia
What is the effect of cardiac glycosides? What is the only one in use?
Positive isotropy
Digoxin (also negative chronotrope)
How does digoxin (cardiac glycoside) work to cause positive isotropy?
Inhibits Na/K pump in cardiomyocytes
Increases intracellular Na, decreases Ca
Causes calcium to move to smooth reticulum
What type of sympathomimetics are used for as positive inotropes? What other effect do they have?
B1 agonists e.g. dobutamine
Also positive chronotrope
What are the adverse effects of sympathomimetics? When may dobuatmine be used?
Tachycardia
Anaesthesia
What 3 dress are used as negative inotropes?
Sympathetic antagonists (Beta blockers) Cholinergic Calcium channel blockers
How do cholinergics cause negative inotropy? What receptor is involved?
Antagonise sympathetic action on cardiomyocytes
M2 receptor
How do calcium channel blockers cause negative chronotropy?
Reduce calcium influx into cell
Reduced contractility
