Anti-dysrhythmics

Question 1

5 Phases of Cardiac Action Potential

Answer 1

(4) Resting Potential
(0) Depolarization Upstroke (Na+ Current)
(1) Early Repolarization
(2) Plateau (Ca2+ current)
(3) Late repolarization (K+ current)

Question 2

Stage 4 of C-AP

Answer 2

-80/85 mV resting membrane potential
-inward rectifying K+ current IK1

Question 3

Stage 0 of C-AP

Answer 3

Electrical impulse of adjacent cell causes=
-Na+ channel open
-Inward current INa
- Depolarization, upstroke.
(above 0mV)

Question 4

Stage 1 of C-AP

Answer 4

Early repolarization by transient outward K+ current Ito.

Question 5

Stage 2 of C-AP

Answer 5

Plateau. Balance between.
-L-type inward Ca2+ current ICal. (depolarization)
and
-Ultra rapid IKur
-Rapid IKr
-Slowly IKs [repolarisation]

Question 6

Stage 3 of C-AP

Answer 6

Repolarization.
Closure of L-type Ca2+ channel.
K+ channels close slowly.
Final repolarization by K+ efflux through the Kir channels (IK1)

Question 7

What is an arrythmia?

Answer 7

Change from the normal sequence of electrical impulses (heart rhythm)
-tachycardia too fast
-bradycardia too slow

Question 8

Class 1 Anti-Dysrhythmic Drugs

Answer 8

Block voltage sensitive Na+ channels.
1a, 1b, 1c subtypes

Question 9

Class 1, 1a

Answer 9

Na+ channel blockade, prolonged repolarization.

For ventricular arrythmias (more)

Question 10

Class 1, 1a Effect on C-AP

Answer 10

Slows depolarization. Extends AP duration delaying repolarization.

Question 11

Class , 1a Example

Answer 11

Quinidine

Question 12

Class 1, 1b

Answer 12

Na+ channel blockade, shortened repolarization.

For ventricular tachycardia, fibrillation.

Question 13

Class 1, 1b effect on C-AP

Answer 13

Depolarization is the same, repolarization happens earlier.

Question 14

Class 1, 1b Example

Answer 14

Lidocaine

Question 15

Class 1, 1c

Answer 15

Na+ channel blockade, repolarization unchanged

Paroxysmal AF

Question 16

Class 1, 1c effect on C-AP

Answer 16

Slows depolarization (not straight up on graph diagonal). No change on repolarization.

Question 17

Class 1, 1c Example

Answer 17

Flecainide

Question 18

Class II Anti-dysrhythmic Drug

Answer 18

B ARs Antagonists (propranolol, atenolol)

For post MI, recurrent tachycardias

Question 19

Class II Function

Answer 19

-decrease inward calcium (slow contraction)
-slow pacemaker function (slow heart rate)

Question 20

Class III Anti-dysrhythmic Drugs

Answer 20

Potassium channel blockers.

D-sotalol, amiodarone

Can cause trosades de pointes, prolonged QT interval. (HERG inhibition?)

Question 21

Class III Function

Answer 21

Extends C-AP duration. Late repolarization. Slows depolarization somewhat.

Proarrhythmic if used in wrong disease state.

Question 22

Class IV Antidysrhymic Drugs

Answer 22

Calcium Channel blocker.

Vepramil, diltiazem