Antiarrhythmics

Question 1

Class IA mechanism

Answer 1

Moderate Na block along with K block

Slows ERP and ADP

Prolongs QT and QRS

Question 2

Class IB mechanism

Answer 2

Mild Na block, no effect on K

Shortens APD by increasing repolarization

No effect of ERM

Question 3

Effective refractory period

Answer 3

The time it takes for sufficient sodium channels to return to resting state, and a new action potential can occur.

Question 4

Action potential duration

Answer 4

The time it takes to return membrane potential to the diastolic resting membrane potential

Question 5

Increased APD

Answer 5

by sustaining a depolarized Em and slowing Na channel recovery will INCREASE the ERP and impair conduction

Question 6

Class I Mechanism of action

Answer 6

Block Na channels

• phase 0 of fast response
• phase 4 of slow

Slow or block conduction and abolish pacemakers

Sometimes effects K channels too

Question 7

Class IA MOA, Ex.

Answer 7

Moderate Na+ AND K+ block
Slows ERP and ADP
prolongs QRS and QT interval
Ex: procainamide, quinidine

Question 8

Class IB MOA, Ex.

Answer 8

Mild Na+ block, NO K+ block
Shortens APD by increaseing repolarization. No effect on ERP
effective for ventricular arrhythmias assoc. w/ depol
Ex: phenytoin (Dilantin), Lidocaine

Question 9

Class IC MOA, Ex.

Answer 9

Marked Na+ block, no K+ blockade
small effects on ERP and ADP
Marked QRS prolongation
Ex: flecainide, propafenone. can be very pro-arhythmic

Question 10

Class III MOA

Answer 10

blocks potassium channels, effects phase 2-3 repolarization in fast response cell
Increases APD and ERP,
phase 4 is not effected like in class I

Question 11

Class III Ex., EKG

Answer 11

amiodarone

delays phase 2-3 repol. prolongs QT interval, no effect on QRS

Question 12

Adenosine MOA

Answer 12

suppresses nodal action potentials via hyperpolarization
increases K+ current, decreases CA++ current
decreases slope of phase 4
inhibits AV nodal conduction and increases refractory period

Question 13

Class II MOA

Answer 13

Beta-1-adrenergic receptor blockers
slows phase 4 depolarization and phase 0 nodal conduction. suppresses AV nodal reentrant arrhythmias and ABN pacemakers
Reduces Na+ and Ca++ current during diastole (slow response)

Question 14

Class II Drugs

Answer 14

Metoprolol
esmolol (IV ONLY)
Propranolol

Question 15

Digoxin

Answer 15

parasympathomimetic - vagal activation which gives ACh- like effects
used in tx of rapid atrial or AV nodal arrhythmias

Question 16

Magnesium

Answer 16

helpful in digoxin induced arrhythmias and cases of torsades de pointe

Question 17

Class IV MOA

Answer 17

Calcium channel blockers, Greater effect in tissue that fires frequently, is more depolarized at rest and are more dependant on Ca++ current for activation
AV/SA nodes are greatly effected - slows phase 0 to prolong AV conduction and ERP

Question 18

Class IV drugs

Answer 18

Verapamil, Diltiazem