Antidysrhythmic drugs

Question 1

What is the mechanism of action for the Class 1 drugs?

Answer 1

Block voltage-sensitive Na channels and reduce depolarization rise

Question 2

What is the mechanism of action for the Class 2 drugs?

Answer 2

Beta adrenoceptor antagonists

Question 3

What is the mechanism of action for the Class 3 drugs?

Answer 3

Prolong the refractory period of the myocardium

Question 4

What is the mechanism of action for the Class 4 drugs?

Answer 4

Calcium antagonists; impair impulse propagation in damaged areas of the myocardium

Question 5

When do Class 1 drugs bind most strongly?

Answer 5

When the Na channels are open or in the refractory state

Question 6

What happens to Class 1 drugs when the Na channels are closed?

Answer 6

It gradually dissociates, so the block resides

Question 7

T/F Class 1b drugs associate and dissociate rapidly

Answer 7

TRUE; within the time of a normal heart beat

Question 8

What is a class 1b drug/

Answer 8

Lidocaine

Question 9

T/F Lidocaine (1B) selectively binds to refractory channels during depolarized ischemic muscle

Answer 9

TRUE

Question 10

What is Lidocaine (1B) useful for?

Answer 10

Control of ventricular dysrhythmias from any reason

Question 11

T/F Class 1C drugs associate/dissociate more quickly than 1B drugs

Answer 11

FALSE; they are slow which means they achieve a steady state block that does not vary with the stage of the cycle

Question 12

What is an example of a 1C drug?

Answer 12

Flecainide

Question 13

What is Flecanide used to treat?

Answer 13

Ventricular tachycardias

Question 14

What are some examples of class 1A drugs?

Answer 14

Quinidine (Horses)

Procainamide (Dog)

Question 15

What species is Quinidine used in? Whats it used for?

Answer 15

Horses
Reverse atrial fibrillation
Indications: supra-ventricular arrhythmias esp atrial fibrillation

Question 16

Procainamide is preferred in what species to do what?

Answer 16

Dogs

Maintenance of ventricular arrhythmias or ventricular tachycardia

Question 17

When would you NOT use Procainamide?

Answer 17

If the patient had a conduction block

Question 18

What is the mechanism of action of the 1A drugs?

Answer 18

Block the Na channels, just like the 1B and 1C drugs

Question 19

What effects do Beta-1 receptos have on the heart?

Answer 19

Increase rate and excitability

Question 20

What mechanism of action do class 2 drugs have?

Answer 20

Beta-1 antagonists

Reduce excitability due to sympathetic overactivity and reduce AV conduction in atrial tachycardias

Question 21

What are examples of Class 2 drugs?

Answer 21

Propranolol

Atenolol

Question 22

T/F PRopranolol is the most common class 2 drug

Answer 22

TRUE

Question 23

What special considerations come with Propranolol?

Answer 23

Bronchial muscle spasm is a possible SE; raise to full level over 3 days

Question 24

What does Propranolol do?

Answer 24

HR decreased
Prevent reflex tachycardia
Lowers blood pressure and reduces ventricular hypertrophy in cardiomyopathy and hyperthyroidism

Question 25

What is Atenolol used for? How is it different than Propranolol?

Answer 25

Used for supraventricular arrhythmias and excessive cardiac hypertrophy May be longer acting

Question 26

What is the special feature of Class 3 drugs? What do these do?

Answer 26

Prolongs the cardiac action potential and icnreases the refractory period Produces pronounces ventricular and supra-ventricular anti-dysrhythmic effects

Question 27

What would you use Class 3 drugs to treat?

Answer 27

Tachycardia

Question 28

What is an example of a Class 3 drug? When would you not want to use this?

Answer 28

Amiodarone Contra-indicated for used with bradycardia

Question 29

What is the mechanism of action for Class 4 drugs?

Answer 29

Block voltage sensitive Ca channels Shorten the plateu phase of the AP and reduce force of contraction Inhibition of Ca suppresses ectopic beats

Question 30

What are some examples of the Class 4 drugs?

Answer 30

Verapamil and Diltiazem

Question 31

What Class 4 drug is preferred for IV administration? Long-term oral administration?

Answer 31

Verapamil for IV Diltiazem: Long-term oral

Question 32

What would you use Class 4 drugs to treat?

Answer 32

Atrial tachycardias

Question 33

How do type 1A drugs differ from Class 1B and 1C drugs?

Answer 33

1A: can be used to treat atrial AND ventricular tachycardias 1b & 1C: Can only be used for ventricular tachycardias All three work by blocking Na channels

Question 34

What could you use to treat an atrial tachycardia?

Answer 34

Qunidine (1A) Horses Propranolol and Atenolol (2) Verapamil and Diltiazem (4)

Question 35

What could you use to treat ventricular tachycardias/

Answer 35

Lidocaine (1B) Flecainaide (1C; vet use probably unlikely) Amiodarone (3) Procainamide (1A) Dogs