Pharmacology: Drugs Affecting Cardiac Rhythm I and II

Question 1

8 prototypical antiarrhythmic drugs per Singh-Vaughan Williams

Answer 1

procainamide, lidocaine, flecainide, atenolol, dofetilide, verapamil, digoxin, adenosine

Question 2

What are targets of Class IA antiarrhythmics and what is the prototypical example of such a drug?

Answer 2

Na, K currents –> procainamide

Question 3

What are targets of Class IB antiarrhythmics and what is the prototypical example of such a drug?

Answer 3

Na current –> lidocaine

Question 4

What are targets of Class IC antiarrhythmics and what is the prototypical example of such a drug?

Answer 4

Na current –> flecainide

Question 5

What are targets of Class II antiarrhythmics and what is the prototypical example of such a drug?

Answer 5

beta blockers –> beta receptor –> Ca, K, F currents –> atenolol

Question 6

What are targets of Class III antiarrhythmics and what is the prototypical example of such a drug?

Answer 6

K current –> dofelitide

Question 7

What are targets of Class IV antiarrhythmics and what is the prototypical example of such a drug?

Answer 7

calcium channel blockers –> Ca current –> verapamil

Question 8

What is adenosine’s target?

Answer 8

P/purinergic - adenosine receptor

Question 9

Drugs used to treat v-tach

Answer 9

Class I and III

Question 10

Drugs used to treat a-fib

Answer 10

Class I and III

Question 11

Drugs used to treat AV reentry

Answer 11

Class I and II and III

Question 12

Drugs used to treat AV nodal reentry

Answer 12

Class II and IV and digoxin and adenosine

Question 13

What are the drug effects that treat reentrant tachycardias?

Answer 13

reduced excitability (except class III), slower conduction velocity (except class III), longer refractory period (except class IB), IA and III increase AP duration

Question 14

What are the drug effects that treat automaticity?

Answer 14

slow down phase 4 depolarization

Question 15

What are the drug effects that treat tachycardia due to early afterdepolarization (e.g. torsades de pointes)

Answer 15

prolong ventricular action potential duration

Question 16

Potency of Class I drugs

Answer 16

1. C>A>B
2. more potent at fast heart rate
3. more potent at depolarized resting membrane potential

Question 17

What factors increase the effect of K current blockade on AP duration? (which drugs do this?)

Answer 17

Class IA and III –>

1. slow heart rate
2. low extracellular K
3. low extracellular Mg

Question 18

What are parasympathetic effects on heart as modulated by digoxin?

Answer 18

reduction in beta-receptor mediated calcium current and increase in muscarinic K current –> more depolarization

Question 19

What are effects on heart as modulated by adenosine?

Answer 19

reduction in beta-receptor mediated calcium current and increase in muscarinic K current –> more depolarization

Question 20

What are the effects of Class II, IV, digoxin, and adenosine on sinus rate, AVN ERP, AVN excitability?

Answer 20

reduce sinus rate, increase refractory period, reduce excitability

Question 21

Which calcium channel blockers selective for cardiac and vascular channels?

Answer 21

verapamil = cardiac
nifedipine = vascular
diltiazem = both

Question 22

How do Class II, IV, digoxin, adenosine affect inotropy?

Answer 22

digoxin is positive, the others are negative

Question 23

3 requirements for reentry

Answer 23

1. potential path
2. unidirectional block
3. slow conduction

Question 24

What is the risk of trying to kill a reentry circuit by causing refractory block –> letting it run into itself?

Answer 24

excessively long APD and torsades de pointes

–> require short excitable gap to work

Question 25

What is the risk of trying to reduce a reentry circuit by causing fixed block --> slowing it down?

Answer 25

slow conduction facilitates reentry --> require low safety factor for this to work

Question 26

What is electrical wavelength?

Answer 26

the distance traveled by a wavefront during the time between depolarization and end of refractory period of start of wave --> ERP * conduction velocity

Question 27

Do smaller wavelengths promote or protect against afib?

Answer 27

promote

Question 28

Drugs that affect cardiac rhythm that are used for nonarrhythmic indications: htn

Answer 28

ca blockers, beta blockers

Question 29

Drugs that affect cardiac rhythm that are used for nonarrhythmic indications: systolic dysfunction

Answer 29

beta blockers, digoxin

Question 30

Drugs that affect cardiac rhythm that are used for nonarrhythmic indications: ischemia

Answer 30

ca blockers, beta blockers

Question 31

Risk of antiarrhythmics in pts with long qt, low K, low Mg

Answer 31

torsade de pointes w/ class IA, III

Question 32

Risk of antiarrhythmics in pts with sick sinus

Answer 32

worse sinus bradycardia w/ class II, IV, digoxin, amiodarone

Question 33

Risk of antiarrhythmics in pts with AV block

Answer 33

higher degree AV block w/ class II, IV, slowed junctional pacers w/ class I, II

Question 34

Risk of antiarrhythmics in pts with poor systolic function

Answer 34

Class I, II, IV are negatively inotropic