Drugs and Arrhytmias

Question 1

explain phases of cardiac action potential in the myocytes

and then

the SA nose

Answer 1

Firstly the SA node and AV node depolarise due to calcium, not sodium and secondly the duration of the cardiac action potential is much greater in the ventricle than either the atria or the nodes.

Question 2

What is lidocaines mechanism of action ?

Answer 2

Sodium channel blocker

Question 3

How do B-Blockers affect heart condition?

Answer 3

The second group of antiarrhythmic drugs are the B-blockers which inhibit conduction in the heart due to blockade of the B-adrenoceptor linked to a cell membrane calcium channel, reducing calcium entry.

Question 4

What is the only CCB that is used to influence cardiac arythmias ?

Answer 4

Verapamil

Now this is often replaced by adenosine

Question 5

How does amiodarone work ?

Answer 5

Block of the potassium channel, delays re-polarisation prolonging the effective refractory period.

Can also block the other channels.

Question 6

What are the adverse effects of amiodarone ?

Answer 6

Heart - By blocking too many channels, it can cause arrhythmias itself.

Question 7

What is digoxins mechanism of action?

Answer 7

Digoxin therapy causes a decrease in functional Na,K-pump concentration of around 25% due to specific inhibition of the Na,K-ATPase.

Digoxin induces an increase in intracellular sodium that will drive an influx of calcium in the heart and cause an increase in contractility.

Question 8

What is the first line of treatment for SVT?

Answer 8

Adenosine

Question 9

How does adenosine work?

What arrhythmia is it used to treat?