Lecture 19: Antiarrhythmic Flashcards
1
Q
Afterdepol
A
When a normal action potential triggers extra abnormal depolarizations / oscillations -> arrhythmias
- Early afterdepolarizations
- Delayed afterdepolarizations
2
Q
Early Afterdepol
A
- Early-afterdepolarizations occur during inciting action potential (phase 2 or 3)
- Triggered by conditions that prolong action potential (eg, drugs that prolong QT interval)
3
Q
Delayed Afterdepol
A
- Delayed-afterdepolarizations occur shortly after the completion of repolarization
- Mechanism not well understood
4
Q
Anti-arrhythmic drugs
A
- Class I (Na+ channel blockers)
- Class II (Beta-blockers)
- Class III (K+ channel blockers)
- Class IV (Ca2+ channel blockers)
5
Q
Class I
A
- Fast channel blockers (Na+)
- Decreased Na+ entry slows rate of rise of Phase 0 depolarization
- Use / state-dependent
- (IA) Quinidine, procainamide, disopyramide
- (IB) Lidocaine, mexiletine
- (IC) Flecainide, propafenone
6
Q
Class II
A
- beta-blockers (Ca2+)
- Propranolol, metoprolol, esmolol
7
Q
Class III
A
- inhibitors of repolarization (K+)
- Amiodarone, sotalol, dofetilide
8
Q
Class IV
A
- calcium channel blockers (Ca2+)
- Verapamil, diltiazem
9
Q
Class IA
A
- Quinidine, Procainamide, Disopyramide
- Slow rate of change of phase 0
- Slowing conduction, prolonging action potential & increasing ventricular effective refractory period
- Intermediate speed of association with activated / inactivated Na+ channels & intermediate rate of dissociation
10
Q
Quinidine
A
- Concomitant Class III activity (block K+ channels)
- Can precipitate arrhythmias
- Due to toxicity is being replaced by Ca2+ antagonists
Clinical Applications
- Conversion and prevention of relapse into atrial fibrillation +/or flutter
- Suppression of supraventricular and ventricular arrhythmias
- Replaced by more effective/safer antiarrhythmic agents
PK
- Quinidine sulfate = rapid oral absorption
- Forms active metabolites (CYP 3A4)
- Inhibits CYP 2D6, 3A4 & P-glycoprotein
Adverse
- Arrhythmias (torsades de pointes)
- SA & AV block or asystole
- Nausea, vomiting & diarrhea (30-50%)
- Thrombocytopenic purpura
- Toxic doses – ventricular tachycardia (exacerbated by hyperkalemia)
- Cinchonism (blurred vision, tinnitus, headache, psychosis)
- Mixed alpha-adrenergic block & antimuscarinic properties
- Can increase [digoxin] by decreasing renal clearance
Contraindications
- Do not use in patients with: Complete heart block
- Use with extreme caution in patients with:
- Prolonged QT interval
- History of Torsades de Pointes
- Incomplete heart block
- Uncompensated heart failure
- Myocarditis
- Severe myocardial damage
- Drug interaction: don’t take quinidine w antacids (will incr absorption and toxicitiy)
11
Q
Procainamide
A
- Derivative of local anesthetic procaine
- Similar actions to quinidine
- Blockade of Na+ channels in activated state
- Blockade of K+ channels
- Antimuscarinic properties
Clinical Applications
- Ventricular arrhythmias
- Due to proarrhythmic effects use should be reserved for life-threatening arrhythmias
PK
- IV
- Metabolized by CYP 2D6
- Partly acetylated to N-acetylprocainamide (NAPA) which prolongs duration of action potential (class III)
Adverse
- Chronic use = high incidence of AE
- Reversible lupus-like syndrome (25-30%)
- Toxic doses: asystole, induction of ventricular arrhythmias
- CNS effects (depression, hallucination, psychosis)
- Weak anticholingeric effects
- Hypotension
Contraindications
- Hypersensitivity
- Complete heart block
- 2nd degree AV block
- SLE in slow acetylators
- Torsades de Pointes
- Heart failure & hypertension (use with caution)
12
Q
Disopyramide
A
MOA
- Strong negative inotropic effect (> quinidine & procainamide)
- Strong antimuscarinic properties
- Causes peripheral vasoconstriction
- Blocks K+ channels
Clinical: Supraventricular and ventricular arrhythmias
Adverse
- Pronounced negative inotropic effects
- Severe antimuscarinic effects (dry-mouth, urinary retention, blurred vision, constipation)
- May induce hypotension & cardiac failure without pre- existing myocardial dysfunction
13
Q
Class IB:antiarrhythmics
A
- Lidocaine, Mexiletine
- Slow Phase 0 & decreases slope of Phase 4
- Shorten Phase 3 repolarization; QT interval: shortened
- Little effect on depolarization phase of action potential in normal cells; QRS: no change
- Rapidly associate and dissociate with Na+ channels
- IB drug are used in settings of:
- Post-MI
- Digoxin toxicity
14
Q
Lidocaine
A
MOA
- Local anesthetic
- More effect on ischemic or diseased tissue
- Particularly useful in treating ventricular arrhythmias
- LITTLE EFFECT on K+ channels
PK: IV only (extensive first-pass metabolism)
Uses
- Acute treatment of ventricular arrhythmias from myocardial infarction or cardiac manipulation (eg, cardiac surgery)
- Lidocaine’s use for VT has declined as a consequence of trials showing IV amiodarone to be superior
- Little effect on atrial or AV junction arrhythmias
Adverse
- Wide toxic-therapeutic ratio
- CNS effects (drowsiness, slurred speech, agitation etc.)
- Little impairment of left ventricular function
- NO negative inotropic effect
- Cardiac arrhythmias (<10%)
- Toxic doses: convulsions, coma
15
Q
Mexiletine
A
- Orally active derivative of lidocaine
- Can be used both orally and IV
Uses: Management of severe ventricular arrhythmias
Adverse Effects: Mainly CNS & GI
16
Q
Class IC antiarrhythmics
A
- Flecainide, Propafenone
- Markedly depress Phase 0 of action potential -> marked slowing of conduction of action potential but, little effect on duration or ventricular effective refractory period
- Associate and re-associate slowly with Na+ channels
- Show prominent effects even at normal heart rates
17
Q
Flecainide
A
- Severe symptomatic ventricular arrhythmias (life- threatening only), premature ventricular contraction or ventricular tachycardia resistant to other therapy
- Severe symptomatic supraventricular arrhythmias & prevention of paroxysmal atrial fibrillation
- Flecainide and propafenone are associated with the potential for fatal ventricular arrhythmias in persons with structural heart disease.
Adverse
- Aggravates CHF (negative inotropic effect)
- CNS effects: dizziness, blurred vision, headache
- GI effects: nausea, vomiting, diarrhea
- Life-threatening arrhythmias & ventricular tachycardia
18
Q
Propafenone
A
Used for treatment of life-threatening ventricular arrhythmias and the maintenance of normal sinus rhythm in patients with symptomatic atrial fibrillation
Adverse
- Similar to flecainide
- Also has Beta-blocking activity therefore bronchospasm, aggravation of underlying heart failure etc.
19
Q
Class II antiarrhythmics
A
- Reduce both heart rate & myocardial contractility (Beta1) by decr SA firing and AV conducting by decr phase 4 of AP
- Slow conduction of impulses through myocardial conducting system
- Reduce rate of spontaneous depolarization in cells with pacemaker activity (block of adrenergic release)
- Little effect on action potential in most myocardial cells
Adverse
- Bradycardia, hypotension, CNS effects etc.
- Contraindicated in acute CHF, severe bradycardia or heart block and severe hyperactive airway disease
20
Q
Propanolol, Metoprolol: Uses
A
- Reduce incidence of sudden arrhythmic death after MI
- Control of supraventricular tachycardias (atrial fibrillation & flutter, AV nodal re-entrant tachycardias)
- Ventricular tachycardias (catecholamine-induced arrhythmias, digoxin toxicity)
21
Q
Esmolol: Uses
A
- Short-acting 1-selective antagonist
- t1/2 =~9min
- Used IV for treatment of acute arrhythmias occurring during surgery or in emergency situations
22
Q
Class III antiarrhythmics
A
- Block repolarizing K+ channels
- Prolong action potential (and QT interval) without altering Phase 0 or resting membrane potential
- Prolong ERP and APD
- All have potential to induce arrhythmias
23
Q
Amiodarone
A
- Related structurally to thyroxine (contains iodine)
- Complex MOA showing Class I, II and III (& some IV) effects
- Dominant effect = K+ channel blockade.
- Decreases AV conduction & sinus node function.
- Blocks mostly inactivated Na+ channels
- Weak Ca2+ channel blocker
- Inhibits adrenergic stimulation (alpha & beta-blocking properties)
- Antianginal & antiarrhythmic activity
Uses
- Used in the management of ventricular & supraventricular arrhythmias
- Amiodarone is the drug of choice for acute VT refractory to cardioversion shock.
- Low doses for maintaining normal sinus rhythm in patients with atrial fibrillation
PK
- Oral (very well absorbed)
- t1/2 = several weeks (extensively distributed in adipose tissue), loading dose required
- Full clinical effects (& adverse effects) may take 6 weeks to achieve
Adverse
- IPF, liver toxicity, GI intolerance, tremor, ataxia, dizziness, hyper- or hypothyroidism, liver toxicity, photosensitivity, neuropathy, muscle weakness, hypotension, bradycardia, AV block, arrhythmias
- blue skin discoloration (iodine accumulation)
- despite prolonging the QT interval, has low incidence of Torsades de Pointes.
Contraindications
- Patients taking: Digoxin, theophylline, warfarin, quinidine
- Patients with:
- Bradycardia
- SA or AV block
- Severe hypotension
- Severe respiratory failure
24
Q
Sotalol
A
MOA
- Potent non-selective Beta-blocker
- Inhibits rapid outward K+ current
- decr SA and AV nodal conduction
- Prolongs repolarization & duration of action potential
- Lengthens refractory period
Uses
- Treatment of life-threatening ventricular arrhythmias
- Maintenance of sinus rhythm in patients with atrial fibrillation & flutter who are currently in sinus rhythm
- Due to pro-arrhythmic effects – do not use for asymptomatic arrhythmias
Adverse
- As for beta-blockers
- Lowest rate (of antiarrhythmics) of acute or long-term adverse effects
- Torsades de pointes (prolongs QT interval)
- Use with caution in patients with renal impairment
25
Q
Dofetilide
A
- Potent and pure K+ channel blocker
Clinical Applications
- Maintenance of normal sinus rhythm in patients with chronic atrial fibrillation / flutter of longer than one week duration who have been converted to normal sinus rhythm
- Conversion of atrial fibrillation / flutter to normal sinus rhythm
PK: Excreted in urine (~80 % unchanged)
Adverse
- Headache, chest pain, dizziness, ventricular tachycardia
- Torsade de Pointes (prolongs QT interval)
26
Q
Class IV antiarrhythmics
A
- Block Ca2+ channels
- Decrease inward Ca2+ current leads to decreased rate of Phase 0 spontaneous depolarization
- Slow conduction in tissues dependent on Ca2+ current (SA & AV nodes)
- Major effects on both vascular & cardiac smooth muscle
27
Q
Verapamil, Diltiazem
A
Verapamil = relatively selective for the myocardium and is less effective as a systemic vasodilator drug
Diltiazem = intermediate selectivity for the myocardium between verapamil and the dihydropyridines
Major Effects:
- Decrease contractility (negative inotropy)
- Decrease heart rate (negative chronotropy)
- Decrease conduction velocity (negative dromotropy)
MOA
- Inhibit voltage-sensitive Ca2+ channels decrease in slow inward current that triggers cardiac contraction
- Bind only to open, depolarized channels, preventing repolarization before drug dissociates
- Use/state-dependent
- Slow conduction & prolong effective refractory period
Uses
- More effective against atrial than ventricular arrhythmias
- Supraventricular tachycardia is major arrhythmia indication
- Reduction of ventricular rate in atrial fibrillation & flutter
- Hypertension, angina
Adverse
- Negative inotropes
- Transient decrease in BP
- CNS effects (headache, fatigue, dizziness)
- GI effects (constipation, nausea)
Contraindications
- Verapamil can increase the concentrations of other cardiovascular drugs such as digoxin, dofetilide, simvastatin, & lovastatin
28
Q
Digoxin
A
- Shortens refractory period in atrial & ventricular myocardial cells
- Prolongs effective refractory period & diminishes conduction velocity in AV node
- Uses: Control of ventricular response rate in atrial fibrillation & flutter with impaired left ventricular function or heart failure
MOA
Heart Failure: Positive inotrope (increases intracellular [Ca2+]i)
Arrhythmias
- Direct AV node blocking effects & vagomimetic properties:
- Inhibition of Ca2+ currents in AV node
- Activation of Ach-mediated K+ currents in atrium
Major indirect actions
- Hyperpolarization
- Shortening of atrial action potentials
- Increases in AV nodal refractoriness
Antiarrhythmic actions
- (1) Slows AV conduction, and
- (2) Prolongs effective refractory period of the AV node
- thereby decreasing the fraction of atrial impulses that are conducted through the node -> useful in treating atrial flutter / fibrillation (by controlling ventricular rate)
Adverse
Toxic doses: Ectopic ventricular beats -> ventricular tachycardia & fibrillation
29
Q
Adenosine
A
- Naturally occurring nucleoside (P1 receptor agonist)
- High doses = decreases conduction velocity & prolongs refractory period as well as decreasing automaticity in AV node
- Very short t1/2 (15 s)
MOA
- Enhances K+ conductance
- Inhibits cAMP-mediated Ca2+ influx
- Leads to hyperpolarization esp. in AV node
- drug of choice for paroxysmal SVT
Uses: IV adenosine = drug of choice for abolishing acute supraventricular tachycardia
Adverse
- SOB
Low toxicity
- Flushing
- Burning
- Chest pain
- Hypotension
- Bronchoconstriction in asthmatics (may persist up to 30 min)
30
Q
Magnesium
A
- Functional Ca2+ antagonist
Used for treatment of:
- Torsades de pointes (prolonged QT interval)
- Digitalis-induced arrhythmia
- Prophylaxis of arrhythmia in acute MI
*
31
Q
Atropine
A
Used in bradyarrhythmias to decrease vagal tone
32
Q
Rate control
A
- negative dromotropic agents
- Ca2+ channel blockers
- Beta-blockers
- Digoxin is DOC in rate control in patients with reduced EF or CHF w A-fib
- Amiodarone (when other agents can’t be used)
33
Q
Rhythm control
A
- Class IC antiarrhythmics, (flecainide, propafenone)
- Class III antiarrhythmics, (amiodarone, dofetilide)
Warnings: Pt can revert back to A-fib
34
Q
Prevention of thromboembolic events
A
- Heparin (IV)
- Unstable patients who require immediate cardioversion
- Warfarin (oral): In stable patients cardioversion should be delayed for 3- 4 weeks until adequate anticoagulation has been achieved
- Control of ventricular rate should be undertaken whilst patient is waiting for cardioversion
- Oral anticoagulants usually continued for at least 4 weeks after procedure
