Drugs for cardiac arrhythmias 2

Question 1

List the classes under I and their sodium channel affinity and rate of dissociation

Answer 1

Class IA Quinidine Open > inactivated Slow
Class IB Lidocaine Inactivated > open Rapid
Class IC Flecainide Open > inactivated Very slow

Question 2

MoA of class la

Answer 2

MoA: slow phase 0 depolarization and phase 3 repolarization, thereby increasing the QRS duration and the QT interval.

Question 3

MoA of class lb

Answer 3

• MOA: inhibit fast sodium channels and shortens action potential duration, thereby inhibiting ectopic beats and re-entry circuits
• little effect on normal cardiac tissue, but they can accelerate phase 3 repolarization and decrease the QT
  interval slightly.

Question 4

Syn for Lidocaine

Answer 4

Lignocaine

Question 5

Lidocaine falls to which type of Anaesthetic

Answer 5

Amide-type local anaesthetic

Question 6

MoA of lidocaine

Answer 6

MOA: inhibit fast sodium channels and shortens action potential duration, thereby inhibiting ectopic beats and re-entry circuits

Question 7

Indications for Lidcaine

Answer 7

Indication: suppression of symptomatic ventricular arrythmias associated with MI, cardiac surgery and other acute situations

Question 8

Evidence shows what with the use of Lidocaine

Answer 8

Note: evidence show trials of prophylactic lidocaine use routinely show increased mortality

Question 9

Lidocaine PKS
1. Onset of action
2. Duration of action
3. Metabolism
4. Excretion

Answer 9

• Onset of action: IV administration = immediate, IM = 5-15 minutes
• Duration of action: IV= 10-20 minutes after initial bolus. IM = 1-1.5 hours
• 90% rapidly metabolised in the liver and excreted in the kidneys (<10% as unchanged drug)
• Hepatic clearance is decreased in hepatic disease and CCF

Question 10

Contra-indications for Lidocaine

Answer 10

Contraindications
* Severe sinus node dysfunction, 2nd or 3rd degree heart block, hypersensitivity to amide type local anaesthetics (LAs )

Question 11

Cautions for Lidocaine

Answer 11

Cautions
* Respiratory depression, other cardiac dysfunction
* Do not use in pregnancy

Question 12

Drug interaction for Lidocaine

Answer 12

Drug interactions
* Other arrhythmias, anticonvulsants, cimetidine

Question 13

Adverse effects for Lidocaine

Answer 13

• Neurological effects (seizures)
• Common: drowsiness, confusion, dizziness
• Uncommon: cardiac effects

Question 14

MoA of Class lc

Answer 14

MoA: greatest effect on phase 0 depolarization and increase the QRS duration markedly, but they have little
effect on phase 3 and the QT interval

Question 15

Class lc should be prescribed by ?
Should not be use when?
Effects of class lc

Answer 15

Only prescribed by an experienced specialist
* Should not be used in ventricular arrhythmias
* Pro-arrhythmic (development of a significant new arrythmia or worsening of an existing arrhythmia) , effects can be fatal, associated with increased mortality

Question 16

MoA of class III

Answer 16

MoA: no effect on phase 0, but they markedly prolong phase 3 and increase the QT interval.

Question 17

Indication for Amiodarone

Answer 17

Indication: prophylaxis and treatment of supra ventricular and ventricular arrhythmias.

Question 18

Amiodarone is an organic iodine compound that is structurally related to what?

Answer 18

Thyroid hormone

Question 19

Amiodarone is the most safest antiarrhythmics agents after using what?

Answer 19

One of the safest antiarrhythmic agent after B-blockers for oral use

Question 20

why is the use of amiodarone is limited

Answer 20

Use is limited due to side effects (including inducing tachy arrhythmias)