Arrhythmias: Anti-Arrhythmic Drugs & Surgery Flashcards
Name the classification system used for antiarrhythmic drugs
Vaughn Williams classification
List the classes of in the Vaughn Williams classification
Ia, Ib, Ic
II
III
IV
Give examples of antiarrhythmic drugs that don’t fit into the Vaughn Williams classification
Digoxin
Adenosine
What is the target of class Ia drugs?
Describe its action
Voltage gated Na+ channel
Associate with and dissociate from Na+ channels at a moderate rate
Slow rate of rise of AP and prolong refractory period
What is the target of class Ib drugs?
Describe its action
Voltage gated Na+ channel
Rapidly associate with and dissociate from Na+ channels
Prevent premature beats
What is the target of class Ic drugs?
Describe its action
Voltage gated Na+ channel
Slowly associate with and dissociate from Na+ channels
Depress conduction
-ve inotropes
What is the target of class II drugs?
Describe its action
β - adrenoceptor (antagonists)
Decrease SA and AV node depolarization rates
What is the target of class III drugs?
Describe its action
Voltage-activated K+ channels (& some others)
Prolong phase 3 duration
(class III act on phase 3)
What is the target of class IV drugs?
Describe its action
Voltage-activated Ca2+ channels
Slow conduction in SA and AV nodes
Less Ca2+ influx during phase 2
- ->
- ve inotropic effect
Which classes of antiarrhythmics act on the atria?
Ic, III
Which classes of antiarrhythmics act on the ventricles?
Ia, Ib, II
Which classes of antiarrhythmics act on the AV node?
II, IV
adenosine, digoxin
Which classes of antiarrhythmics act on the atria and ventricles, and AV accessory pathways?
Ia, Ic
Amiodarone, sotalol
What phase of the action potential do class I drugs effect?
Phase 0 in fast response cells
as phase 0 is due to Na+
What phase of the action potential do class II drugs effect?
Phase 0 in slow response cells
What phase of the action potential do class III drugs effect?
Phase 3
as phase 3 is due to K+
What phase of the action potential do class IV drugs effect?
Phase 2 in fast response cells
Phase 0 in slow response cells
(as these are due to Ca2+)
In what states of the voltage dependant Na+ channel do class 1 drugs bind?
- Open
- Inactivated
- Resting
Class 1 drugs bind to voltage dependant Na+ channels in their open and inactivated states
They dissociate during the resting state
Do class 1 drugs preferentially bind to myocytes with higher or lower firing frequencies?
They bind preferentially to areas of high firing frequency
Why do class I drugs preferentially bind to ischaemic tissue and ectopic foci?
Ischaemia --> longer action potentials --> less time for Na+ channel in its resting state --> class I drugs are bound for longer --> Higher affinity for class I
(can be the same logic for ectopic foci)
What is radiofrequency catheter ablation?
What does it target?
What can it be done straight after?
Ablation of cardiac tissue with catheter
Can target part of a reentrant circuit or a ectopic foci
Can be done in the same procedure as an electrophysiological study
Describe a single chamber pacemaker
Only paces the right atria or right ventricle
Describe a dual chamber pacemaker
Paces the right atrium and right ventricle
- used for AV node disease
Describe an implantable cardioverter defibrillator (ICD)
Does:
- Pacing
- Cardioversion
- Defibrillation
Can get dual chamber ICDs
What is the difference between an ICD and a pacemaker?
ICD can shock you back into rhythm
Pacemaker can’t
What does a pacemaker do?
Paces the heart rate
Describe direct current cardioversion (DCCV)
DC shocks via external electrodes
Need sedation/analgesia
Used during fibrillation to restore NSR
(antiarrhythmic drugs can be given at the same time)
