Antiarrhythmic Drugs

Question 1

What is the threshold voltage for caridomyocytes?

Answer 1

-40mV. Voltage gated sodium channels open, causing rapid depolarisation.

Question 2

What are the two origins of tachyarrhythmias?

Answer 2

Re-entry (most common)
Enhanced automaticity (cardiac cell ability to generate spontaneous action potential through leaky channels)

Question 3

What is re-entry tachycardia?

Answer 3

Premature beating of the heart due to a re-entrant circuit (extra pathway for transduction).

Question 4

What are the 4 classes of antiarrhythmic drugs?

Answer 4

Class 1: Na+ channel blockers
Class 2: Beta-ADR blockers
Class 3: Prolong effective refractory period
Class 4: Ca2+ channel blockers

Question 5

How do Na+ channel blockers work?

Answer 5

It takes time for cells to raise the membrane potential to the subsequent threshold. Slowing the rise of membrane potential slows myocardial tissue conduction.

The sum of all delays is the conduction time.

Question 6

Give an example of a sodium channel blocker/

Answer 6

Lignocaine.

Question 7

How do beta-ADR blockers prevent arrhythmia?

Answer 7

Beta blockers block sympathetic activity, reducing heartrate.

Question 8

Give examples of beta blockers.

Answer 8

Metoprolol, atenolol

Question 9

Give an example of a drug that lengthens effective refractory period (ERP)

Answer 9

Amiodarone.

Question 10

How does adenosine work on cardiomyocytes?

Answer 10

Adenosine receptor linked K+ channels exists on atrial and AV conduction tissue.

Adenosine lowers RMP by allowing more K+ to leave the cell. A lower RMP makes it harder for cell to reach threshold.