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Drugs: From molecule to man > ELM 15: Dysrhythmias - VW drug classification > Flashcards

ELM 15: Dysrhythmias - VW drug classification Flashcards

1
Q

Risk factors for dysrhythmias

A
  • Too much alcohol
  • Smoking
  • Genetics
  • Obesity
  • Congenital abnormalities
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2
Q

What is an arrhythmia?

A

Absence of rhythm

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3
Q

What is a dysrhythmia?

A

Disturbance in rhythm

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4
Q

What are the 3 main effects of Sympathetic Autonomic Nervous System on the Heart

A
  • Increase slope of pacemaker potential in SA node (Inc HR)
  • Increased force of contraction due to Inc intracellular Ca2+
  • Increased conduction velocity through AV node
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5
Q

What do the different components of an ECG trace represent?

A

P wave = Atrial activation
QRS complex = Ventricular activation
T wave = Recovery wave

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6
Q

What is wolff-parkinson-white syndrome

A
  • Congenital abnormality with an accessory AV pathway
  • Global re-entry circuit
  • No rate limiter in kent bundle so causes atrial and ventricular fibrillation
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7
Q

What is heart block?

A
  • Form of bradycardia
  • Damage to AV node impairs atrial to ventricular conduction
    3 degrees:
    1 = slow conduction, PQ increased and QRS for every P wave
    2 = miss QRS complexes
    3 = impulses dont get from atria to ventricles
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8
Q

What is paroxysmal supraventricular tachycardia?

A
  • Re-entry circuit through AV node
  • Starts at teens-40s
  • Ventricular rate of 250bpm
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9
Q

What is the Singh-Vaughan Williams system for antidysrhythmic drugs?

A

Divides antidysrhythmic drugs according to mechanism of action

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10
Q

What is the target and examples of Class I antidysrhythmic drugs?

A
  • Sodium channels
    1a = Disopyramide
    1b = Lidocaine
    1c = Flecainide
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11
Q

What is the target and examples of Class II antidysrhythmic drugs?

A

Beta 1 adrenoceptor
- Atenolol
- Bisoprolol
- Propranolol

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12
Q

What is the target and examples of Class III antidysthrythmic drugs?

A

Potassium channels
- Amiodarone
- Sotalol
- Dronedarone

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13
Q

What is the target and examples of Class IV antidysrhythmic drugs?

A

Calcium channels
- Verapamil
- Diltiazem

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14
Q

What is the target and examples of unclassified antidysrhythmic drugs?

A

Various targets
- Adenosine
- Atropine
- Digoxin

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15
Q

What are some weaknesses of the Vaughan Williams classification system?

A
  • Some drugs have multiple action sites
  • Action sites can be different in healthy and diseased tissue
  • Doesn’t include lots of useful drugs
  • Some dysrhythmias can be treated with drugs form more than one class
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16
Q

What is a more modern alternative system for the Vaughan Williams system?

A

Lei et al system
Has 7 classes

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17
Q

How do Class IA dysrhythmic drugs work?

A

EG Disopyramide
- Moderate Na+ channel block
- Blocks K+ efflux
- Increased effective refractory period
- Increase action potential duration

18
Q

How do Class IB antidysrhythmic drugs work?

A

EG Lidocaine
- Weak Na+ channel block
- Promotes K+ efflux
- Decreased effective refractory period
- Decreased action potential duration

19
Q

How do Class IC antidysrhythmic drugs work?

A

EG Flecainide
- Strong Na+ channel block
- No effect on K+ efflux
- No change in effective refractory period
- No change in action potential duration

20
Q

What are the characteristics of the Class IA drug disopyramide?

A
  • Intermediate dissociation rate
  • Prevent ventricular and supraventricular dysrhythmias
  • Used after heart attack or defibrillation
21
Q

What are the side effects of Class Ia drug disopyramide?

A
  • GI tract problems
  • Arrhythmias
  • Cognitive problems
  • Visual problems
  • Urinary disorders
  • Hypotension
  • Contraindicated in heart block and severe heart failure
22
Q

What are the characteristics of the class Ib drug licodaine?

A
  • Binds to inactivated sodium channels
  • Fast dissociation
  • Also used as local anaesthetic
  • Given intravenously to suppress ventricular dysrhythmias
  • Used after defibrillation
23
Q

What are some side effects of the class Ib drug lidocaine?

A
  • CNS excitation
  • CNS depression at high doses
  • Bradycardia, hypotension and dysrhythmias
  • Contraindicated in Wolf-Parkinson-White, severe heart block
24
Q

What are some characteristics of class Ic drug flecainide?

A
  • Slow dissociation
  • Used for supraventricular and ventricular arrhythmias under specialist supervision
25
Q

What are some side effects of class Ic drug flecainide?

A
  • Dysrhythmias
  • Oedema
  • Visual disturbances
  • Contraindicated after heart attack as it increases risk of sudden death
26
Q

What are the characteristics of class II drug atenolol?

A
  • Reduces automaticity, slows SA and AV node conduction
  • Useful in dysrhythmias triggered by SNS activation like atrial fibrillation and supraventricular tachycardias
  • Prevents dysrhythmias after heart attack
  • Used for thyrotoxicosis
27
Q

What are the side effects of Class II drug atenolol?

A
  • Bronchoconstriction
  • Precipitation of heart attack failure, block
  • Masks sympathetic signs of hypoglycaemia in T1 diabetes
  • Decreased mobilisation of glucose from glycogen in diabetes
  • Decreased insulin sensitivity in T2 diabetes
  • Can cause cold extremities and raynauds
28
Q

What is the mechanism of the Class III drug amiodarone?

A
  • In class III as a K+ channel blocker but also inhibits beta adrenoceptors and sodium channels and blocks calcium channels
  • Blocks potassium channels to delay repolarisation
  • Increased action potential duration and refractory period
  • Decreased AV node conduction velocity and re-entry tendency
29
Q

What are the indications for class III drug amiodarobe?

A
  • Used in range of dysrhythmias
  • Given orally or IV
30
Q

What are some side effects of class III drug amiodarone

A
  • Worsen bradycardias or AV node block
  • Cause TdP
  • Analogue of thyroxine and can interfere with thyroid function
  • Cause lung fibrosis
  • Deposited in eye and causes visual problems
  • Liver toxicity
  • Deposited in skin and causes blue gray colour when exposed to UV
  • Long 100 day plasma half life
  • Long time to reach steady state
31
Q

What are the indications for Class IV drug verapamil?

A
  • Oral, IV formulations
  • Prevents or terminates PSVT
  • Controls ventricular rate in AF
  • Angina, hypertension, cluster headaches
32
Q

What are some side effects of Class IV drug verapamil?

A
  • Headache constipation flushing and hypotension
  • Contraindicated in Wolf-parkinson-white, bradycardia, heartblock
  • Broken down by CYP3A4 in body
33
Q

What is CYP3A4?

A
  • Cyt P450 enzyme expressed in liver and intestines that metabolises drugs
  • Irreversibly inhibited by furanocoumarins found in fruit
  • Inhibition can cause overdose on prescription drugs
34
Q

Examples of drugs broken down by CYP3AR

A

Ritonavir
Diazepam
Sertraline
Verapamil

35
Q

What is the mechanism of the unclassified drug adenosine?

A
  • Can bind to 4 GPCR subtypes
  • A1 A2A A2B A3
36
Q

Which pathways are used by the 4 GPCR subtypes adenosine can bind to?

A

A1 = Gi via GIRK KACh
A2a A2b = Gs
A3 = Gi/Gq

37
Q

What are the indications of the unclassified drug adenosine?

A
  • Short 10 second plasma half life
  • Rapid uptake by RBC and metabolism
  • Suppresses PSVT, ventricular tachycardia with WPW syndrome, supraventricular tachycardias in surgery
38
Q

What is the mechanism of the unclassified drug digoxin

A
  • Directly blocks sodium pump
  • Indirectly blocks sodium/calcium exchange
  • Increases calcium in stores which causes more contraction force
  • Stimulates PNS
  • Increases AV node refractory period but decreases it in myocytes
  • Increases force of contraction, slows ventricles for better filling
39
Q

What are the indications for unclassified drug digoxin?

A
  • Heart failure
  • Persistent atrial fibrillation
40
Q

What is the mechanism of unclassified drug atropine?

A
  • Competitive antagonist at M2 receptor
  • M2 receptor slows heart rate so inhibition will increase heart rate
41
Q

What are the indications of unclassified drug atropine?

A
  • IV in bradycardia and heart block

Drugs: From molecule to man (21 decks)

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