Bradyarrhythmia and inotropy pharmacology

Question 1

What is AV block?

Answer 1

Interruption of impulse from atria to ventricles

Question 2

What is sick synus syndrome?

Answer 2

Dysfunctional SAN

Question 3

What is atrial standstill?

Answer 3

Failure of atrial depolarisation - temporary/permanent lack of atrial activity

Question 4

What is a problem with all CV pharmacology?

Answer 4

Combination of problems and side effects - patients rarely have one condition

Question 5

Are bradyarrhythmias more or less common than tachyarrhythmias? What may bradyarrhythmias require?

Answer 5

Less common

Pacemaker

Question 6

How does the body physiologically increase heart rate? Why is this a problem for bradyarrhythmic pharmacology?

Answer 6

Increased sympathetic nervous system activity
Pathway broken (unlike in tachycardia)

Question 7

What are the 4 categories of positive chronotropes used to treat bradyarrhythmias?

Answer 7

Sympathomimetics
Anticholinergics
Methylxanthine
PDE III inhibitors

Question 8

How do methylxanthines work?

Answer 8

Reduce hyperpolarisation of cell through potassium channels

Question 9

Give an example of a methylxanthine?

Answer 9

Theophylline

Question 10

What does PDE do? What is PDE III?

Answer 10

Degrade intracellular cAMP

Heart specific PDE

Question 11

What happens if PDE is inhibited?

Answer 11

Increased intracellular cAMP
Activates protein kinase
Phosphorylates calcium
Stronger contractions

Question 12

Give an example of a PDE III inhibitor

Answer 12

Pimobendan

Question 13

What are the 2 types of sympathomimetics? Give an example of each

Answer 13

B1 agonists - dobutamine

B2 agonists - terbutaline

Question 14

What effects do B1 agonists have?

Answer 14

Positive chronotropy

Positive inotropy

Question 15

What effects do B2 agonists have?

Answer 15

Positive chronotropy

Positive dromotropy

Question 16

What effect do anticholinergics have? What can they be used for?

Answer 16

Positive chronotrope
Positive dromotrope
Short term anaesthesia

Question 17

Give an example of an anitcholinergic

Answer 17

Atropine

Question 18

What are the 3 categories of positive inotropes?

Answer 18

Sympathomimetics
PDE III inhibitors
Cardiac glycosides
(Anticholinergics, glucagon)

Question 19

How do positive inotropes generally cause increased contractility?

Answer 19

Mimic/enhance sympathetic activity
Increase intracellular Ca2+
Increases EDVV

Question 20

PDE III inhibitors are positive chronotropes and inotropes. What other effects do they cause?

Answer 20

Vasodilation

Faster depolarisation

Question 21

How do PDE III inhibitors cause vasodilation?

Answer 21

Increased intracellular cAMP
Dephosphorylates MLCK
Smooth muscle relaxation

Question 22

What effects does pimobendan have?

Answer 22

Positive inotrope

Vasodilator

Question 23

How is pimobendan administered? Where is it metabolised/activated and excreted?

Answer 23

Oral or parenteral
Activated in liver
Excreted in faeces

Question 24

What are the side effects of pimobendan?

Answer 24

Inappetance
Lethargy
Dyspnoea
Azotaemia

Question 25

What is the effect of cardiac glycosides? What is the only one in use?

Answer 25

Positive isotropy | Digoxin (also negative chronotrope)

Question 26

How does digoxin (cardiac glycoside) work to cause positive isotropy?

Answer 26

Inhibits Na/K pump in cardiomyocytes Increases intracellular Na, decreases Ca Causes calcium to move to smooth reticulum

Question 27

What type of sympathomimetics are used for as positive inotropes? What other effect do they have?

Answer 27

B1 agonists e.g. dobutamine | Also positive chronotrope

Question 28

What are the adverse effects of sympathomimetics? When may dobuatmine be used?

Answer 28

Tachycardia | Anaesthesia

Question 29

What 3 dress are used as negative inotropes?

Answer 29

``` Sympathetic antagonists (Beta blockers) Cholinergic Calcium channel blockers ```

Question 30

How do cholinergics cause negative inotropy? What receptor is involved?

Answer 30

Antagonise sympathetic action on cardiomyocytes | M2 receptor

Question 31

How do calcium channel blockers cause negative chronotropy?

Answer 31

Reduce calcium influx into cell | Reduced contractility