CV pharmacology bradyarrhythmias

Question 1

What is bradyarrhythmia. Most commonly one seen in practise

Answer 1

1. abnormally slow HR

2. AV block

Question 2

Issue with treating Bradyarrhythmia

Answer 2

o Normal animal see activation of sympathetic system to inc HR
o The problem for pharmacological intervention is that usually in these cases the pathway is broken so drugs don’t work very well for long term management☹
o Also lots of side effects

Question 3

What drugs do we use to treat bradyarrhythmias?

Answer 3

1. Sympathomimetics - mimic action of SNS
2. Anticholinergics - reduce effect of PNS
3. Methylxanthines
4. PDE III inhibitors - inc cAMP in cell

Question 4

What affect to Methylxanthines have

Answer 4

1. PhosphoDi Esterase inhibition
2. Block adenosine action
3. which speeds up the rise of the pacemaker potential by reducing hyperpolarisation of the cell (through K channels)
4. basically by blocking action adenosin in heart, it acts on cAMP – how it speeds up depolarisation

Question 5

Autonomic Drugs

Answer 5

1. Sympathomimetics
2. Anticholinergics
3. Methylxanthines
4. PDE III inhibitors

Question 6

Which drugs come under sympathomimetics?

Answer 6

1. Beta 1 agonists a) act to increase firing of the SAN
   b) Main drug dobutamine (used in anaesthesia)
2. Beta 2 agonists - some cross over with beta 1
   a) Terbutaline (see resp lectures)
   b) +ve chronotropy and +ve dromotropy (improve conduction)

Question 7

Talk about beta 1 agonist drugs

Answer 7

1. Autonomic drugs, sympathomimetics
2. Main drug dobutamine (used in anaesthesia)
3. o Also positive inotropic, increase contractility therefore myocardial O2 consumption – important where tissue perfusion is poor

Question 8

Talk about Anticholinergics

Answer 8

1. Group of autonomic drug
2. Muscarinic antagonist
3. E.g. Atropine often used under anaesthesia, especially brachycephalic breeds to inc HR
4. Muscarinic antagonist (M1-5)
5. short term use (anaesthesia)
6. +ve chronotropy (inc HR) & dromotropy

Question 9

What type of drug is atropine adn when used?

Answer 9

Autonomic anticholinergic.

Often used under anaesthesia, especially as pre medication for brachycephalic breeds to increase HR

Question 10

talk about Methylxanthines

Answer 10

1. Type of autonomic drug
2. E.g. Theophylline
3. Non-selective Phospho Di Esterase inhibition
4. Adenosine antagonist - adenosine slows the rise of the pacemaker potential by inducing hyperpolarisation of the cell (through K channels)

Question 11

Talk about PDE III inhibitors

Answer 11

1. Type of autonomic drug
2. e.g. Pimobendan – mostly used for positive inotrophic effects also positive conotroph – inc cAMP inside cell, inc heart rate