Drugs to treat arrhythmias II

Question 1

Class III MOA

Answer 1

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

Question 2

Why is the use of Amiodiorone limited?

Answer 2

Use is limited due to side effects (incl. tachy arrhythmia)

But it is one of the safest antiarrhythmic agent after B-blockers for oral use

Question 3

Indications of amiodarone

Answer 3

prophylaxis and treatment of supra ventricular and ventricular arrhythmias

Question 4

Explain Amiodarone structure

Answer 4

Amiodarone is an organic iodine compound that is structurally related to thyroid hormone

Question 5

Oral absorption, bioavailability and distribution of Amiodarone

Answer 5

Slow oral absorption with bioavailability of 20-55%
Wide distribution in fat, muscles and Liver.

Question 6

How long does the therapeutic effect of Amiodarone take?

Answer 6

Therapeutic response may take 3 weeks, with peak effect reached in
1-5 months

Question 7

After withdrawal of tx with amiodarone, how long do antiarrhythmic effects persist?

Answer 7

Antiarrhythmic effect persist for 10 – 150 days after withdrawal of
long-term treatment

Question 8

Onset of action of amiodarone

Answer 8

IV 10-15 minutes

Question 9

Metabolism and excretion of Amiodarone

Answer 9

Extensive hepatic metabolism with biliary excretion (renal excretion
negligible)

Question 10

Contraindications of Amiodarone (40

Answer 10

Cardiac bradycardia/block, hyperthyroidism, sensitivity to iodine,
hypokalemia
Pregnancy and lactation

Question 11

Cautions of Amiodarone

Answer 11

Heart failure, hepatic impairment

Question 12

Drug interactions of Amiodarone

Answer 12

May interact with other drugs for months after
discontinuation of treatment
* Other antiarrhythmics, b-blockers, digoxin, drugs causing QT prolongation,
phenytoin, simvastatin, warfarin, grapefruit juice

Question 13

Amiodarone adverse effects

Answer 13

May take several weeks to appear and continue for months after
discontinuation of treatment
* Torsades de Pointes
* Hyper/hypothyroidism (thyroid function monitoring necessary)
* Neurotoxicity (including peripheral neuropathies)
* Photosensitivity (warn to avoid exposure to sunlight)
* GI
* Uncommon: pulmonary fibrosis & hypersensitivity pneumonitis

Question 14

Effects of Class II and Class IV antidysrhythmic drugs

Answer 14

Class II drugs (β-adrenoceptor antagonists) and Class IV drugs (calcium channel blockers) slow phase 4 depolarization in the SA node and increase the PP
interval.

They also slow the atrioventricular (AV) node conduction velocity and increase
the PR interval.

Question 15

MOA of propranolol (5)

Answer 15

Inhibit sympathetic activation of cardiac automaticity and conduction,
* Slow the heart rate,
* Decrease the AV node conduction velocity, and
* Increase the AV node refractory period,
* Little effect on ventricular conduction and repolarization.

Question 16

Indications of Propranolol

Answer 16

• Prevent and treat supraventricular dysrhythmias
• Reduce ventricular ectopic depolarizations and sudden death in patients
  with myocardial infarction.

Question 17

MOA of Verapamil (4)

Answer 17

Decrease the AV node conduction velocity and
* Increase the AV node refractory period,
* Smaller effect on the SA node and heart rate,
* Little effect on the ventricular conduction velocity and refractory
period.

Question 18

Indications of Verapamil

Answer 18

Controlling or converting certain supraventricular dysrhythmias, not
effective in treating ventricular dysrhythmias.
* Control the ventricular rate in patients with atrial fibrillation

Question 19

ROA of Verapamil

Answer 19

Verapamil can be administered intravenously to terminate paroxysmal
supraventricular tachycardia (PSVT), and it is given orally for chronic
treatment

Question 20

Adverse effects of Verapamil

Answer 20

Exacerbate wide QRS complex VT and should not be given to patients
with this dysrhythmia.

Question 21

List 5 miscellaneous antiarrhythmics (ADMIR)

Answer 21

• Adenosine
• Digoxin
• Magnesium sulphate
• Ivabradine &
  Ranolazine

Question 22

What is adenosine used for?

Answer 22

Acute management of paroxysmal supraventricular tachycardias
convert to sinus rhythm

Question 23

ROA and half-life of Adenosine

Answer 23

Administer as rapid IV bolus
* Half-life <10 seconds

Question 24

Adverse effects of Adenosine (3)

Answer 24

dyspnoea, flushing, chest pain are an indication the
bolus has reached the heart

Only use when cardiac monitoring and resuscitation is available

Question 25

What is atrial fibrillation and atrial flutter

Answer 25

disorganized form of re-entry in which atrial cells are continuously re-excited by re-entrant stimuli as soon as they are
repolarized.
The AV node is continuously bombarded with atrial impulses, some of which are conducted to the ventricles, so that the
ventricular rate is often rapid and irregular

Question 26

What are the objectives of treatment of atrial fibrillation and flutter

Answer 26

1. Ventricular rate control to avoid development of cardiomyopathy. Use B-blockers and CCBs which slow AV node conduction velocity and increase its refractory period, so that fewer impulses are conducted to the ventricles.
2. Prevent recurrences and maintain normal sinus rhythm -Amiodarone.

3.Anticoagulant (warfarin) to prevent thromboembolism and stroke

Question 27

What is Torsades de Pointes?

Answer 27

Polymorphic ventricular
tachycardia (VT), associated with
QTc prolongation, which is the heart rate adjusted lengthening
of the QT interval.

Question 28

What induces Torsade de Pointes? (3)

Answer 28

• Drugs (including tricyclic
  antidepressants and
  antipsychotic agents )
• Electrolyte abnormalities that
  prolong the QT interval and predispose cardiac cells to afterdepolarizations
• Congenital prolonged QT syndrome.

Question 29

Tx of Torsades de Pointes

Answer 29

Withdrawal of the causative agent,
* Correction of any
electrolyte abnormalities,
such as hypokalemia,
* Intravenous administration
of magnesium sulfate IV ,
and
* Cardiac overdrive pacing.
* These treatments act in part by shortening the QT
interval.