Antiarrhythmic Drugs

Question 1

Which ions are involved in the…

1. SA node AP
2. Ventricular and Atrial AP

Answer 1

1. Ca dependent AP = Ca comes in to depolarize, K goes out to repolarize. Spontaneous depolarization.
2. Na goes in to depolarize , Ca comes in to make plateau, K goes out to repolarize.

Question 2

Bradycardias

Answer 2

Slow heart rate - too few beats per minute
The CO is decreased so not enough blood is pumped (can pass out)
Treat with pacemakers

Question 3

Tachycardias

Answer 3

Fast heart rate - too many beats per minute
Heart beats too quickly to fill properly (also decreases CO and can lead to heart failure)
Drug therapy used

Question 4

3 Non drug treatments of arrhythmias

Answer 4

1. Remove abnormal tissue (catheter ablation)
2. Pacemaker
3. Implantable cardioverter-defibrillator

Question 5

4 Classes and functions of antiarrhythmic drugs

Answer 5

Class 1: Na channel blocker
Class 2: Beta blocker
Class 3: Increase in action potential duration (increase refractory period)
Class 4: Ca channel blocker

Treat tachycardias. Class 1 and 3 can especially cause arrhythmias.

Question 6

Enhanced Automaticity

Answer 6

Can occur in cells that normally show spontaneous depolarization (SA and AV nodal cells)
Can occur in muscle cells that do not show spontaneous depolarization (ectopic pacemaker - develops at site thats not the SA node - it can take over control of heart beat)
If an ectopic pacemaker is going faster than the SA node then it can take over and cause a tachycardia.

Question 7

Triggered Automaticity

Answer 7

A normal AP can be followed by an abnormal AP when heart cells are overloaded with calcium (digoxin does this)
1. Early afterdepolarizations (attach onto the normal one)
2. Delayed afterdepolarization
(excess Ca triggers extra AP)

Question 8

Re-entry

Answer 8

Occurs when one AP activates the heart more than once.

You get it from having a 1 way conduction block.

Question 9

Class 1 drugs

Answer 9

Sodium channel blockers.
They preferentially bind to and block Na channels in cardia tissue that is damaged and firing rapidly.
They turn a one way block into a 2 way block so that no re entry can occur.
Give after a heart attack.

Question 10

Class 2 and 4 drugs

Answer 10

2 = beta-adrenergic blockers. 4= Ca channel blockers.

1. Pain/stress activates the SNS and increase Ca influx into heart cells, which can promote Ca overload and trigger DADs/EADs (Beta blockers block receptors at heart - lessen Ca overload and stop the arrhythmias. Ca blockers block channels in heart to decrease Ca overload)
2. They both also slow HR, slow conduction velocity through AV node, and increase AV refractory period

Question 11

Class 3 drugs

Answer 11

Prolong AP duration and refractory period by blocking K channels responsible for repolarizing the heart.
Even if re entry occurs, the normal tissue is in refractory period, so no second AP happens.

Question 12

Digoxin

Answer 12

Mimics the effect of PNS in the heart, especially at the AV node.
Acts like the beta blockers and Ca channel blockers - slows AV conduction and decreases ventricular rate.