Anti-arrhythmics

Question 1

What is the function of Class 1 arrhythmics?

Answer 1

• Rhythm control
• They block sodium channels that are responsible for the rising phase (Phase 0) of cardiac action potentials.
• They are frequency dependent and voltage dependent.

Question 2

What are the primary effects of Class 1 AADs on the cardiac action potential?

Answer 2

1. They increase the threshold for activation of a cell
2. They reduce Vmax, the rate of the rise of the action potential.
3. They increase the effective refractory period.

Question 3

What is the function of Class 1A AADs?

Answer 3

• Reduction in repetitive firing through increased threshold and frequency dependent block.
• Reduces Vmax
• Prolongs APD and ERP
• Binding/unbinding is immediate``

Question 4

What is the function of Class 1B AADs?

Answer 4

• Reduction in repetitive firing by increased threshold and frequency dependent block.
• Little effect on Vmax
• Binding/unbinding is rapid

Question 5

What is the funciton of Class 1C AADs?

Answer 5

• Reduction in repetitive firing by increased threshold and frequency dependent block
• Larger reduction in Vmax than Class 1A
• Little effect on ERP
• Binding/unbinding is slow

Question 6

Toxicities of Class 1 AADs

Answer 6

• TI is low in most Class 1 drugs.
• Reduced Vmax can cause slowed conduction/arrhythmic APs
• Ventricular arrythmias are a dangerous SAE

Question 7

Which Class 1 drugs have the most toxicities?

Answer 7

Class 1C > Class 1A > Class 1B

Question 8

What are the Class 1A Drugs?

Answer 8

Procainamide
Quinidine
Disopyramide

Question 9

Procainamide

Answer 9

• increases threshold, reduces repetitive firing, reduces Vmax, and increases ERP
• used for A-flutter, A-fib, PSVT, V-tach, and V-fib
• SAE: Arganulocytosis, SLE-like Syndrome, nausea, hypotension

Question 10

Quinidine

Answer 10

• increases threshold, reduces repetitive firing, reduces Vmax, and increases ERP
• used for A-flutter, A-fib, and PSVT, can be used to prevent V-tachyarrythmias
• SAE: diarrhea, cinchonism - including headaches and tinnitus

Question 11

Disopyramide

Answer 11

• similar to quinidine

- used to maintain sinus rhythm in pts with A-flutter, A-fib or to prevent the recurrence of V-tach or V-fib

Question 12

What are the Class 1B antiarrhythmics?

Answer 12

Lidocaine
Tocainide
Mexiletine

Question 13

Lidocaine

Answer 13

• increases threshold, reduces repetitive firing
• little effect on Vmax or ERP
• IV only
• used for IV control of ventricular arrhythmias
• SAE: rare at therapeutic levels; can include CNS symptoms at high plasma levels

Question 14

Tocainide/Mexiletine

Answer 14

• similar to lidocaine but can be used orally

Question 15

What are the Class 1C AADs?

Answer 15

Flecainide

Propafenone

Question 16

Flecainide

Answer 16

• increases threshold and reduces repetitive firing, reduces Vmax
• little effect on ERP
• used for atrial arrhythmias only
• SAE: serious cardiac toxicity

Question 17

Propafenone

Answer 17

• increases threshold and reduces repetitive firing, reduces Vmax
• little effect on ERP
• used in chronic oral therapy for pts with SVTs including A-fib
• metabolized by P450: drug-drug interactions!!!

Question 18

What is the function of Class III AADs?

Answer 18

Used for rhythmcontrol and have three common effects:

1. K+ channel blockade
2. Delayed repolarization
3. Prolonged action potential and prolonged ERP

Question 19

Amiodarone

Answer 19

• Class III/Class I hybrid
• blocks Na+ and K+ channels
• prolongation of action potential duration, increased ERP, reduced Vmax and reduced conduction velocity at high doses
• LONG half life - accumulates in lipids and can cause serious side effects
• used IV for conversion to sinus rhythm as well as orally for ventricular arrythmias and SVTs.
• SAE: pulmonary fibrosis (most serious), headaches, tremor, ataxia, paresthesias, also rare CV side effects

Question 20

Dronedarone

Answer 20

• Class III/Class I hybrid similar to amiodarone
• used for a-tach, a-fib, and v-tach
• SAE: more rare than with amiodarone

Question 21

Dofetilide

Answer 21

• Class III AAD that blocks K+ channel responsible for the early phase of the AP via the IKr current
• prolongs AP duration and ERP
• used to maintain sinus rhythm in A-flutter and A-fib

Question 22

Ibutilide

Answer 22

• Class III AAD that is similar to dofetilide
• IV only
• used for conversion of A-flutter and A-fib
• SAE: can cause prolonged QT

Question 23

Sotalol

Answer 23

• beta antagonist and K+ channel blocker
• prolongs action potential duration and ERP
• used to treat ventricular tachycardias and SVTs
• SAE: can be arrythmogenic, long QT syndrome, and V-tach

Question 24

What are Class II and Class IV AADs used for?

Answer 24

Rate control

Question 25

What are the effects of Class II AADs?

Answer 25

• beta-antagonists.
• reduce heart rate and the rate of impulse propagation
• used primarily to treat SVTs
• use with care in pts with signs of HF because beta blockers can block compensatory SNS stimulation

Question 26

What are the Class II AADs?

Answer 26

Nonselective: propranolol, carvedilol
Beta 1: metoprolol, esmolol
HCN blocker: Ivabridine
Adenosine

Question 27

Ivabridine

Answer 27

• HCN blocker
• reduces heart rate and slope of diastolic depolarization without reducing ventricular contractility
• used for inappropriate sinus tach

Question 28

Adenosine

Answer 28

• stops atrial arrhythmias that involve re-entry from the AV node
• rapid onset and rapid reversal
• used for acute conversion of re-enterant SVTs. NOT USED FOR A-FIB

Question 29

What is the function of Class IV AADs?

Answer 29

• rate control

- Ca2+ channel blockers

Question 30

List the Class IV AADs in order of their frequency dependence

Answer 30

Verapamil > diltiazem > nifedipine

Question 31

List the Class IV AADs in order of their voltage dependence

Answer 31

Nifedipine > diltiazem = verapamil

Question 32

Verapamil