Pharmacological Treatment of Dysrhythmias

Question 1

what causes delayed after depolarisation event? what are examples of places with high intracellular calcium levels?

Answer 1

small peak of activity driven by calcium or calcium triggering places where you have high intracellular calcium levels:

• areas of ischaemic damage
• areas with high calcium deposits

Question 2

what is the vaughan williams system of drugs used to treat dysrhythmias?

Answer 2

1a, b and c-sodium channel blockers all different types depending on what stage they bind to the voltage gated sodium channels and how strong or weak they affect
2- beta adrenoreceptor blockers
3-potassium channel blockers
4-calcium antagonists

Question 3

What are the 2 drugs unclassified on the VW scale but used to treat dysrhythmias?

Answer 3

• adenosine

- digoxin

Question 4

what is the mechanism of action of class 1 sodium channel antagonists?

Answer 4

• inhibit action potential propagation and reduce the rate of cardiac depolarisation in phase 1
• change where threshold will be so need a greater than normal voltage to cause depolarisation= decreasing ectopic events
• elongates the action potential

Question 5

class 1 drugs are use-dependent. what does this mean?

Answer 5

• effectiveness of these drugs will increase as the rate of opening and closing of these voltage gated sodium channels occurs
• more frequent depolarisations= more effective drugs
• hence if you get a faster than normal rate of depolarisation occurring then the effectiveness of these drugs will increase to restore a normal rhythm

Question 6

what is an example of a 1a drug? what are its clinical uses?

Answer 6

• Disopramide

- ventricular dysrhythmias, prevention of recurrent atrial fibrillation

Question 7

what is an example of a 1b drug? what are its clinical uses?

Answer 7

• lignocaine

- treatment/prevention of ventricular tachycardia and fibrillation during and immediately after MI

Question 8

what is an example of a 1c drug? what is its clinical use?

Answer 8

• flecanide

- suppresses ventricular ectopic beats

Question 9

what are the side effects/dangers of using antidysrhythmic drugs?

Answer 9

-given at wrong concentration they can cause dysrhythmias since they alter conduction pathways

Question 10

what are the dangers of using class 1 drugs?

Answer 10

• decrease contractility of the heart

- change rate of depolarisation occurring and the amount of calcium taken back into cell decreasing the SV

Question 11

how do b adrenoreceptors normally function?

Answer 11

• G protein coupled receptor attached to B1/2 receptor
• catecholamine binds stimulating cAMP production and Protein Kinase A will modify calcium channels and alter where we store calcium in cell altering contractility

Question 12

what is the mechanism of action of class 2 drugs?

Answer 12

• blocking reduces influx of Ca into the cell decreases contractility
• SA and AV node are under innervation by sympathetic nervous system blocking these channels increases refractory period and deals contraction through the AV node

Question 13

what is an example of a class 2 drug?

Answer 13

Sotalol

Question 14

what are the clinical uses of class 2 drugs?

Answer 14

• reduce mortality following MI

- prevent recurrence of tachycardias

Question 15

what is special about the class 2 drug stall?

Answer 15

it also has class 3 drug properties

Question 16

what is the mechanism of action of class 3 drugs?

Answer 16

act on signal which repolarises our membrane
block K by blocking K channels results in prolonging the QT interval
prolonging QT interval you increase cardiac cells refractory state

Question 17

what is the clinical use of class 3 drugs?

Answer 17

-preventing or reducing affect of re-entry mechanisms which lead to dysrhythmias

Question 18

what is the disadvantage of using class 3 drugs?

Answer 18

• prolong the QT interval
• increase the time for calcium fluxing into the cell
• higher intracellular calcium levels can lead to dysrhythmias

Question 19

what is an example of a class 3 drug? what is it used to treat?

Answer 19

• amiodarone
• wolf parkinson white syndrome
• supraventricular and ventricular tachyarrythmias

Question 20

what are the two types of calcium antagonist?

Answer 20

• DHP blockers

- rate limiting

Question 21

what are 2 examples of rate limiting calcium antagonists? what are they used to treat?

Answer 21

• verapamil and diltiazem

- reduce tachycardias and dysrhythmias

Question 22

What is the mechanism of action of the rate limiting calcium channel antagonists?

Answer 22

• block calcium channels which maintain plateau of ventricular depolarisation, so shorten plateau phase= less Ca influx= lower intracellular Ca= lower force of contraction
• DHP Ca channels in nodal tissue so slow conduction through SA and AV pathways changes speed at which heart is working

Question 23

what are class 4 drugs used to treat?

Answer 23

• prevent supra ventricular tachycardia

- useful for patients with atrial fibrillation

Question 24

where are adenosine receptors located? what happens if bound to?

Answer 24

• Av node and on cardiac muscle cells

- cAMP activates protein kinase which phosphorylates channels

Question 25

what happens if adenosine binds to a1 receptors on AV node?

Answer 25

hyper polarise conducting tissue slowing HR decreasing pacemaker activity

Question 26

what is adenosine used to treat?

Answer 26

used to terminate supraventricular tachycardias

Question 27

what are the two mechanisms of action of digoxin?

Answer 27

• increase vagus activity slowing heart rate down

- changes what happens with calcium storage

Question 28

what is there disadvantage of using digoxin?

Answer 28

inhibits NaK pump can cause ectopic beats due to chucking out of Na and Ca in