Drugs to treat arrhythmias I

Question 1

List the types of cardiac arrhythmias (Sinus rhythms, ventricular rhythms, and atrial rhythms)

Answer 1

Sinus: Brady (<60) Tachy (>100)

Ventricular rhythms (V-Tach and V-fib)

Atrial rhythms:(supraventricular tachycardia SVT)
* Atrial flutter
* Atrial fibrillation
Ventricular rhythms
* Ventricular tachycardia (V-tach)
* Ventricular fibrillation (V-fib)
* AV nodal re-entrant tachycardia

Question 2

What are the general considerations for treatment of cardiac arrhythmias (2)

Answer 2

Antiarrhythmic may suppress arrhythmias successfully, but
paradoxically increase mortality.

Question 3

Which classes of antiarrhythmic drugs should be used?

Answer 3

Class I and III

Question 4

Describe the function of each class of antiarrhythmic drugs.

Answer 4

• Class I: drugs that block voltage
  sensitive sodium channels. They
  are subdivided: Ia, Ib and Ic
• Class II: β-adrenoceptor
  antagonists
• Class III: drugs that substantially
  prolong the cardiac action
  potential
• Class IV: calcium antagonist

Question 5

Examples of Class Ia drugs

Answer 5

Disopyramide,
quinidine,
procainamide

Question 6

MOA of Class 1a drugs

Answer 6

Sodium channel block (intermediate dissociation) – prolong action potential
duration

Question 7

Example of class Ib drug and MOA

Answer 7

Lidocaine
Sodium channel block (fast dissociation)
shorten action potential duration

Question 8

Example of class Ic and effects

Answer 8

Flecainide
Sodium channel block (slow dissociation)
do not affect action potential duration

Question 9

Example of class II and MOA

Answer 9

PROPRANOLOL
B-blocker

Question 10

Example of class III and MOA

Answer 10

Amiodarone
Potassium channel block - prolong duration
of cardiac action potential

Question 11

Example of class IV and MOA

Answer 11

Verapimil
Calcium channel block – block slow inward
calcium channel of SA and AV nodes

Question 12

MOA of class Ia

Answer 12

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

Question 13

Class Ib MOA

Answer 13

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 14

What type of drug is Lidocaine?

Answer 14

Amide-type local anaesthetic

Question 15

MOA of Lidocaine

Answer 15

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

Question 16

Indications for lidocaine

Answer 16

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

Question 17

ROA of lidocaine and the onset of action associated with each ROA.

Answer 17

IV administration = immediate, IM = 5-15 minutes

Question 18

Duration of action of Lidocaine IV and IM respectively

Answer 18

IV= 10-20 minutes after initial bolus. IM = 1-1.5
hours

Question 19

Metabolism and excretion of Lidocaine

Answer 19

90% rapidly metabolised in the liver and excreted in the kidneys
(<10% as unchanged drug)

Question 20

What decreases hepatic clearance of Lidocaine?

Answer 20

Hepatic disease and CCF

Question 21

Contraindications of Lidocaine (3)

Answer 21

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

Question 22

Cautions of Lidocaine (3)

Answer 22

1. Respiratory depression, 2. other cardiac dysfunction
   3* Do not use in pregnancy

Question 23

Drug interactions of Lidocaine

Answer 23

Other arrhythmias, anticonvulsants, cimetidine

Question 24

Lidocaine adverse effects

Answer 24

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

Question 25

MOA of class Ic

Answer 25

Greatest effect on depolarisation and increase the QRS duration markedly, but they have little effect on phase 3 and QT interval

Question 26

Class Ic drugs are only prescribed by an experienced therapist, and should not be used in __________________

Answer 26

Ventricular arrhythmias

Question 27

Why shouldn’t class Ic be used in ventricular arrhythmias?

Answer 27

Pro-arrhythmic (development of a significant new arrhythmia or worsening of an existing arrhythmia) , effects can be fatal, associated
with increased mortality.