Antidysrhythmic drugs 2

Question 1

Class 1 drugs are divided into 3 subclasses

Answer 1

1) 1A

2) 1B

3) 1C

Question 2

Class 1 drugs

Answer 2

voltage gated sodium channels which is their primary mechanism of action but some have secondary effects on potassium channels involved in repolarization

key role in phase 0

Question 3

Where do class 1 drugs act?

Answer 3

non-nodal tissues eg: atrial, ventricular muscle

Question 3

What class is lidocaine?

Answer 3

1B

Question 4

When is lidocaine used?

Answer 4

ventricular dysrhythmias in acute settings

Question 5

Is lidocaine used in heartattacks?

Answer 5

no, replaced by amiodarone

Question 6

What does lidocaine target

Answer 6

selectively targets inactivated channels more common in ischaemic tissues

Question 7

lidocaine intravenous properties

Answer 7

rapid action and short duration

Question 8

Side effects of lidocaine

Answer 8

seizures, coma, death at higher doses, makes heart block worse

Question 9

Lidocaine as a local anaesthetic

Answer 9

drug is widely used as a local anaesthetic

lidocaine injected near nerves where it blocks voltage-gated sodium channels that are essential for generating action potentials in pain-sensing neurons

by preventing these neurons from generating action potentials lidocaine effectively stops the transmission of pain signals to the central nervous system providing localized pain relief

Question 10

What class is Flecainide?

Answer 10

1C

Question 11

Flecainide

Answer 11

not used as local anaesthetic

binds to open state (longer duration)

good for supraventricular tachycardias eg: atrial fibrillation

available in tablet form

Question 12

Flecainide side effects

Answer 12

fewer CNS side effects but can still lead to dizziness, fatigue, visual disturbances

Question 13

When is Flecainide dangerous?

Answer 13

patients who have structural heart damage can trigger ventricular tachycardia/fibrillation

use is limited

ALL antidysrhythmic drugs have potential to cause dysrthymias

Question 14

Class 2 drugs

Answer 14

the actions of beta 1 adrenoceptors, influences the pacemaker potential (phase 4), the depolarisation phase (phase 0) and in cardiac muscle, the plateau phase (phase 2)

Question 15

Plateau phase

Answer 15

actions on the plateau phase result in increased force of contraction (positive inotropic effect)

blocking this effect is important in the actions of beta blockers in ischaemic heart disease

Question 15

Beta blockers

Answer 15

action of drugs as antagonists of beta 1 adrenoceptor expressed in the heart

Question 16

Which phases important for antidysrhymic actions of class 2 drugs?

Answer 16

effects on phase 4 and phase 0

Question 17

Phase 4

Answer 17

increased sympathetic activity increases the slope of the pacemaker potential

this causes the cell to reach threshold sooner and the end result is that we are able to fire action potentials more frequently

Question 18

How do beta blockers work?

Answer 18

One of the primary mechanisms of beta blockers is blocking the effects of the sympathetic nervous system and reducing the slope of the pacemaker potential in the SA node

this slows the heart and is therefore termed a negative chronotropic effect

useful in treating sinus tachycardias such as those caused by anxiety or hyperthyroidism.

by slowing the pacemaker potential beta blockers reduce the rate at which the SA node fires effectively lowering the heart rate

actions on the pacemaker potential also help to suppress ectopic pacemaker activity in both the atria and ventricles which can be beneficial in preventing ventricular tachycardias in susceptible patients.

in the AV node the sympathetic nervous system increases the activity of L-type calcium channels during Phase 0 of the action potential speeding up AV node conduction and shortening its refractory period

beta blockers counter these effects slowing AV node conduction and prolonging its refractory period

this makes beta blockers effective in controlling ventricular rates in patients with atrial fibrillation or atrial flutter where the transmission of rapid atrial impulses to the ventricles can be very dangerous

Question 19

Side effects of the beta blockers

Answer 19

they can cause bradycardia and can worsen AV node block and can precipitate heart failure

Question 20

What class is Amiodaron?

Answer 20

Class 3 but can be placed in any class

Question 21

Amiodaron with potassium channels

Answer 21

by blocking potassium channels amiodarone prolongs the action potential duration and increases the refractory period, the phase during which the heart is unable to fire another action potential

this extended refractory period reduces the likelihood of abnormal electrical activity and re-entrant dysrhythmias, helping to regulate heart rhythm and reduce the heart rate

Question 22

Benefits of multifaceted action

Answer 22

amiodarone is used in a broad range of dysrhythmias, including atrial fibrillation, atrial flutter, ventricular tachycardias, and in emergency situations for pharmacological cardioversion of ventricular fibrillation

Question 23

Advantages of amiodaron

Answer 23

can be administered both orally (tablet form) and intravenously the use of amiodarone is limited by its extensive side effect profile, multiple contraindications, and complex pharmacokinetics, which include a very long half-life, potential for accumulation in tissues and extensive interactions with other drugs

Question 24

Pharmacokinetics of amiodarone

Answer 24

amiodarone is highly lipophilic, meaning it is deposited in fatty tissues so it takes a long time for plasma levels to stabilize requiring extended dosing before therapeutic effects are fully realized In emergency situations this limitation can be overcome by administering a large dose intravenously over a short period of time when a patient discontinues amiodarone the drug remains in the system for an extended period due to its accumulation in tissues amiodarone has a plasma half-life of approximately 100 days, meaning it takes over three months for plasma levels to decrease by 50% after stopping the drug. Another significant pharmacokinetic issue with amiodarone is its metabolism by the CYP3A4 enzyme which metabolizes over 30% of all drugs this creates a high potential for drug interactions certain dietary components can inhibit this enzyme

Question 25

Side effects of amiodarone

Answer 25

due to its high lipophilicity amiodarone is heavily deposited in various tissues leading to significant side effects lungs: can result in pulmonary fibrosis (scarring), which affects up to 10% of long-term users and can be life-threatening eyes: amiodarone can cause visual disturbances liver: hepatotoxicity skin: exposure to UV light can cause a blue-grey discoloration amiodarone also has high iodine content and this can lead to iodine overload, which disrupts thyroid gland function can cause bradycardia and worsen heart block can trigger a serious dysrhythmia known as Torsades de Pointes in some patients

Question 25

What class is Verapamil in?

Answer 25

Class 4