Antiarrhythmic pharmacology

Question 1

Speed of upstroke proportional to…

Answer 1

Speed of conduction

Question 2

EAD

Answer 2

When action potential is too long, Ca can reactivate and cause an Early after depolarization

Question 3

DAD

Answer 3

Result from fast HR and B stimulation. Extra Ca in cell. So NCX works really hard. Is electrogenic, Na comes in and depolarizes cell.

Question 4

Reentry

Answer 4

Cycling around tissue that has depolarized. Can increase wavelength to make this less possible.

Question 5

Does the center of a reentry loop have to be anatomically defined?

Answer 5

No, can be functionally defined too.

Question 6

Mechanisms of most the the important arrhythmias?

Answer 6

Are initiated by EAD/DAD and maintained by reentry.

Question 7

Strategies for treating arrhythmias

Answer 7

Block Ca current to prevent EADS
block B adrenergic stimulation to decrease Ca in cells
Block Na channels to prevent DADs
Increase wavelength by prolonging action potentials

Question 8

How to determine wavelength?

Answer 8

CV*APD. Increase in APD will increase wavelength and promote reentry termination.

Question 9

Vaughan Williams Classification Systyem Class I

Answer 9

I: Blocks Na currents
A: Rate of unblock medium, IKr block strong. Medium reduction in upstroke velocity, prolong action potentials
B: Rate of unblock fast, IKr block weak. Small reduction in upstroke velocity. Small decrease in APD.
C: Rate of unblock slow, IKr weak. Large reduction in upstroke velocity. No change in APD.

Question 10

Class II Antiarrhythmics

Answer 10

Beta blockers (propranolol). Will decrease HR. Prevent Ca overload and DADs

Question 11

Class III Antiarrhythmics

Answer 11

Blocks IKr, prolongs APD. Amiodarone**

Question 12

Class IV Antiarrhythmics

Answer 12

Blocks Ca channels. Decreases EADS and DADs by decreasing Ca2+overload. verapamil and diltiazem.