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Cardiac arrhythmia drugs Flashcards

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1
Q

What must happen in order for the heart to function effectively?

A
  • Heart needs to contract sequentially (atria then ventricles) and synchronously
  • Relaxation must occur between contractions
  • Coordination of heartbeat is a result of a complex coordinated sequence of changes in membrane potentials and electrical discharges in various heart tissues
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2
Q

How does excitation spread throughout the heart normally?

A
  • Sinoatrial node
  • Passes through atria to AV node
  • Passes through septum via Purkinje fibres
  • ## Right and left bundle branches
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3
Q

Which section of an ECG represents the atrial contraction?

A
  • P wave
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4
Q

Which section of an ECG represents the ventricular contraction?

A
  • QRS complex
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5
Q

Which section of an ECG represents ventricular repolarisation?

A
  • T wave
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6
Q

What maintains resting potential of the heart?

A
  • Transmembrane electrical gradient is maintained
  • Interior of cell is negative with respect to outside of cell
  • Caused by unequal distribution of ions inside vs outside cell
  • Na+ much higher outside cell than inside cell
  • Ca2+ much higher outside cell than inside cell
  • K+ much higher inside cell than outside cell
  • Maintained by ion selective channels, active pumps and exchangers
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7
Q

Outline the fast cardiac action potential

A
  • Phase 0: depolarisation due to influx of Na+
  • Phase 1: early repolarisation due to outward movement of K+
  • Phase 2: plateau due to Ca2+ influx (from sarcoplasmic reticulum)
  • Phase 3: repolarisation due to efflux of K+
  • Phase 4: resting phase
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8
Q

What is the effect of class 1 drugs?

A
  • Slows phase 0
  • Prevents influx of Na+
  • Slows conduction in tissue
  • Minor effects on action potential duration
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9
Q

What is the effect of class 2 drugs?

A
  • Diminishes phase 4 depolarisation and automaticity
  • Beta blockers
  • AP duration slightly lengthened
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10
Q

Give some examples of class 3 drugs

A
  • Amiodarone
  • Dofetilide
  • Sotalol
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11
Q

What is the effect of class 3 drugs?

A
  • Block K+ channels
  • Prolong phase 3 repolarisation without altering phase 0
  • Increase effective refractory period
  • Increase AP duration
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12
Q

What is the effect of class 4 drugs?

A
  • Calcium channel blockers
  • Cause decrease in inward Ca2+ currents
  • Slow phase 4 spontaneous depolarisation
  • Affect plateau phase of action potential
  • Slow conduction in tissues dependent on calcium currents e.g. AV node
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13
Q

Outline the slow cardiac action potential

A
  • Funny current leads to spontaneous depolarisation (slow Na+ channels) in phase 4
  • Calcium influx leads to depolarisation in phase 0
  • Potassium efflux in phase 3 leads to repolarisation
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14
Q

How do calcium channel blockers affect the slow cardiac action potential?

A
  • Slows down conduction velocity
  • Refractory period increases
  • Takes longer for next heartbeat to occur
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15
Q

Which drugs affect automaticity?

A
  • Beta agonists
  • Muscarinic agonists
  • Adenosine
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16
Q

Outline the mechanisms of arrhythmogenesis (abnormal impulse generation)

A
  • Abnormal impulse generation
  • Leads to automatic rhythms such as enhanced normal automaticity (increased APs from SA node) and ectopic focus (AP arises from sites other than SA node)
  • OR triggered rhythms (delayed afterdepolarisations or early afterdepolarisations)
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17
Q

Outline the mechanisms of arrhythmogenesis (abnormal conduction)

A
  • Conduction block - can be first degree, second degree, third degree
  • Re-entry - circus movement and reflection
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18
Q

Outline how abnormal anatomic conduction occurs

A
  • Some patients are born with an extra circuit that connects the atria and ventricles
  • Present only in small populations
  • Leads to pre-excitation
  • Wolf-Parkinson-White syndrome
  • See a delta wave on ECG and palpitations
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19
Q

Outline AV nodal re-entrant tachycardia

A
  • Most common supraventricular tachycardia
  • Involves a slow pathway and a fast pathway in right atrium
  • Can occur around a scar
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20
Q

Outline the action of drugs that treat abnormal generation of arrhythmias?

A
  • Decrease phase 4 slope
  • In pacemaker cells
  • Raises threshold
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21
Q

Outline the action of drugs that treat arrhythmias due to abnormal conduction

A
  • Decrease conduction velocity
  • Increases effective refractory period
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22
Q

What are the goals for treating arrhythmias?

A
  • Restore normal sinus rhythm and conduction
  • Prevent more serious and possibly lethal arrhythmias from occurring
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23
Q

What are the uses of antiarrhythmic drugs?

A
  • Decrease conduction velocity
  • Change duration of effective resting potential
  • Suppress abnormal automaticity
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24
Q

Give some examples of class 1B agents

A
  • Lidocaine - iv only
  • Mexiletine - orally
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25
What are the effects of class 1B agents on cardiac activity?
- Fast binding offset kinetics - No change in phase 0 in normal tissue (no tonic block) - Action potential duration slightly decreased - Increase threshold that needs to be reached before Na+ channels need to be activated - Decrease phase 0 conduction in fast beating or ischaemic tissue
26
What are the effects of class 1B agents on ECG?
- None in normal - Increased QRS in fast beating or ischaemic tissue
27
What are the uses of class 1B agents?
- Acute: ventricular tachycardia (especially during ischaemia) - Not used in atrial arrhythmias or AV junctional arrhythmias
28
What are the side effects of class 1B agents?
- Dizziness - Drowsiness - Abdominal upset
29
Give some examples of class 1C agents
- Flecainide (propafenone) - Can be taken orally or IV
30
What are the effects of class 1C agents on cardiac activity?
- Very slow binding offset kinetics (>10s) - Substantially decreases phase 0 (Na+ conduction) - Decrease automaticity and increase threshold - Increase action potential duration (K+) and refractory period, especially in rapidly depolarising atrial tissue
31
What are the effects of class 1C agents on ECG?
- Increased PR interval - Increased QRS complex - Increased QT interval
32
What are the uses of class 1C drugs?
- Wide spectrum - Used for supraventricular arrhythmias (fibrillation and flutter) - Premature ventricular contractions - Wolf-Parkinson-White syndrome
33
What are the side effects of class 1C drugs?
- Pro-arrhythmia and sudden death (especially with chronic use and in structural heart disease) - Increased ventricular response to supraventricular arrhythmias (flecainide flutter) - CNS and gastrointestinal effects
34
Give some examples of class II agents
- Propranolol - oral and IV - Bisoprolol - oral - Metoprolol - 5mg IV, oral too - Esmolol - IV only (very short half life)
35
What are the cardiac effects of class II agents?
- Increased APD and refractory period in AV node to slow Av conduction velocity - Decrease phase 4 depolarised agent (catecholamine dependent)
36
What are the effects of class II agents on ECG?
- Increased PR interval - Decreased HR
37
What are the uses of class II agents?
- Treating sinus and catecholamine dependent tachycardia - Converting re-entrant arrhythmias at AV node - Protecting ventricles from high atrial rates (slow AV conduction) in atrial flutter or atrial fibrillation
38
What are the side effects of Class II agents?
- Bronchospasm - Hypotension - Don't use in partial AV block or acute heart failure
39
Give some examples of Class III agents
- Amiodarone - oral or IV (long half life) - Sotalol - oral absorption
40
What are the cardiac effects of class III agents?
- Increase refractory period and action potential duration by slowing K+ movement - Decrease phase 0 and conduction (Na+) - Increase threshold - Decrease phase 4 (beta block and calcium channels blocked) - Decrease speed of AV conduction
41
What are the effects of class III agents on ECG?
- Increase PR interval - Increase QRS complex - Increase QT interval - Decrease HR
42
What are the uses of amiodarone?
- Very wide spectrum but useful for most arrhythmias
43
What are the side effects of amiodarone?
- Many serious side effects that may increase with time - Pulmonary fibrosis - Hepatic injury - Increase LDL cholesterol - Thyroid disease May need to reduce dose of digoxin and monitor warfarin more closely
44
What are the cardiac effects of sotalol?
- Increases action potential duration and refractory period in atrial and ventricular tissue - Slow phase 4 (beta blocker) - Slow AV conduction
45
What are the effects of sotalol on the ECG?
- Increases QT interval - Decrease HR
46
What are the uses of sotalol?
- Wide spectrum - Supraventricular and ventricular tachycardia
47
What are the side effects of sotalol?
- Proarrhythmic - Fatigue - Insomnia
48
What are some examples of class IV agents?
- Verapamil - oral or IV - Diltiazem - oral
49
What are the cardiac effects of class IV agents?
- Slow conduction through AV (Ca2+) - Increase refractory period in AV node - Increase slop of phase 4 in SA to slow HR
50
What are the effects of class IV agents on ECG?
- Increased PR interval - Increased or decreased HR (depends on BP response and baroreflex)
51
What are the uses of class IV agents?
- Control ventricles during supraventricular tachycardia - Convert supraventricular tachycardia (re-entry around AV)
52
What are the side effects of class IV drugs?
- Caution when partial AV block is present. Can get asystole if beta blocker is on board - Caution when hypotension, decreased cardiac output or sick sinus - Some gastrointestinal problems
53
Outline the administration of adenosine
- Rapid IV bolus - Very short half life (seconds)
54
What is the mechanism of action of adenosine?
- Natural nucleoside that binds A1 receptors - Blocks adenylyl cyclase - Reduces cAMP - Activates K+ currents in AV and SA node - Causes hyperpolarisation - Decreases HR - Leads to decreased Ca2+ currents - Increases refractory period in AV node
55
What are the cardiac effects of adenosine?
- Slows AV conduction
56
What are the uses of adenosine?
- Convert re-entrant supraventricular arrhythmias - Diagnosis of coronary artery disease
57
How is ivabradine administered?
- Orally in 2.5mg bd - Dosing up to 10 mg bd
58
What is the mechanism of action of ivabradine?
- Blocks funny current ion channels highly expressed in sinus node
59
What are the cardiac effects of ivabradine?
- Slows sinus node - BP not affected
60
What are the side effects of ivabradine?
- Flashing lights - Teratogenicity not known
61
What are the uses of ivabradine?
- Reduce inappropriate sinus tachycardia - Reduce heart rate in heart failure and angina
62
What is the mechanism of action of digoxin?
- Enhances vagal activity - Increases K+ currents and decreases Ca2+ currents to increase refractory period - Slows AV conduction - Slows HR
63
What are the uses of digoxin?
- Treatment to reduce ventricular rates in atrial fibrillation and flutter
64
What is the mechanism of action of atropine?
- Selective muscarinic antagonist
65
What are the cardiac effects of atropine?
- Block vagal activity to speed AV conduction and increase HR - Used to treat vagal bradycardia
66
Which drugs should be prescribed for AF?
For rate control: - Bisoprolol first line - Verapamil if asthma - Diltiazem and digoxin For rhythm control: - Sotalol - Flecainide with bisoprolol - Amiodarone
67
Should flecainide be used alone in atrial flutter?
- No - Give AV nodal blocking drugs to reduce ventricular rates in atrial flutter
68
Which IV drugs are given to treat ventricular tachycardia?
- Depends on what drugs have already been prescribed - IV metoprolol if not on bisoprolol - IV lignocaine if not on mexiletine - Amiodarone if not taking it and already on bisoprolol/mexiletine - IV metoprolol/lignocaine or amiodarone
69
What is the best drug to treat Wolf-Parkinson-White syndrome?
- Flecainide - (Amiodarone) - Avoid AV nodal blocking drugs due to risk of pre-excited AF and therefore VF
70
Which drugs are used acutely in re-entrant narrow complex tachycardia?
- Adenosine - Verapamil - Flecainide
71
Which drugs are used to treat chronic re-entrant narrow complex tachycardia?
- Bisoprolol, verapamil - Sotalol - Flecainide - Amiodarone
72
Which drugs are given to treat ectopic beats?
- Bisoprolol first line - Calcium channel blockers if asthma - Flecainide and sotalol with amiodarone last resort
73
Which drugs are used to treat sinus tachycardia?
- Ivabradine - Bisoprolol, verapamil

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