15a - CV

Question 1

Describe the phases of cardiac action potential

Answer 1

Phase:
0 = Fast Na+ channels, rapid depolarisation
1 = Na+ closes, K+ outflux partial repolarisation
2 = Ca2+ slow inward, plateau
3 = Ca2+ close, K+ outflow, repolarisation quick
4 = Slow Na+ + Ca2+ inward

Question 2

What is a cardiac arrhythmia?

Answer 2

Any deviation in heart beat pattern

Question 3

What are class 1 antiarrhythmic drugs?
- Give an example of a drug.

Answer 3

Blocks Na+ channels and prolong AP duration which extends refractory period. Reduced depolarisation rate in phase 0.
- Lignocaine.

Question 4

What are class 2 antiarrhythmic drugs?

Answer 4

Beta-blockers. Affects sympathetic tone which otherwise would’ve increased Ca2+ availability so blocking it will increase refractory period.
Note: Ca2+ used in AV and SV nodes.

Question 5

What are class 3 antiarrhythmic drugs?
- Give an example

Answer 5

K+ channel blockers. Delays repolarisation which increases APD (action potential duration) and ERP (effective refractory period).
- Amiodarone

Question 6

What are class 4 antiarrhythmic drugs?
- Give an example

Answer 6

Ca2+ channel blockers.
- Slowls HR (SA node)
- Produces AV block
- Reduced contraction force
- e.g. Verapamil and Diltiazem

Question 7

Describe Digoxin mechanism as a CV drug

Answer 7

Increases vagal tone which slows HR and blocks AV conduction. Problem is narrow therapeutic range.