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Cardio CP1 > 7 Antiarrhythmia drugs > Flashcards

7 Antiarrhythmia drugs Flashcards

1
Q

Describe the Vaughan Williams classification of antiarrhythmic drugs

A
  • I= Na channel blockers
    • IA=moderate potency
    • IB= least potent
    • IC= most potent
  • II= Beta adrenergic blockers
  • III= K channel blockers
  • IV= Ca channel blockers
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2
Q

What are the direct effects of class IA drugs? What are the indirect effects?

A
  • Direct: Primarily block Na channels:
    • Increase AP threshold
    • Decrease Vmax
    • Increase ERP= increase AP duration
  • Indirect:
    • blocks K channels -> EADs
    • vagolytic effect (“brakes” on the PNS -> faster signal from atria to ventricles/through AV node)
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3
Q

What are 3 main class IA drugs?

A

Na channel blockers:

quinidine, procainamide, disopyramide

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4
Q

What are some side effects of IA drugs?

A
  • severe GI effects (quinidine)
  • vagolytic effect on heart
  • proarrhythmic (prolongs QT)
  • metabolized in the liver (quinidine… ok for pts with renal failure)
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5
Q

What are some drug interactions for class IA drugs?

A
  • inhibit CYP2D6 (decreased metabolism of narcotics)
  • reduced renal clearance of digitalis
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6
Q

What are 2 class IB drugs?

A

Lidocaine and mexiletine

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7
Q

What are the direct effects of class IB drugs?

A
  • increase AP threshold
  • block Na channels (decrease Vmax)
    • at high HR **use dependent
    • and in depolarized cells (high affinity for inactivated Na channel; can target diseased/ischemic cells well)
  • decreases AP duration/ERP
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8
Q

What are some side effects of class IB drugs?

A
  • CNS toxicity (neurons rely on Na!); dizziness, drowsiness, seizures
  • GI toxicity; nausea, vomiting
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9
Q

When are class IB drugs used?

A
  • V tach
  • digitalis induced arrhythmias

**safe for patients with long QT syndrome (shortens AP)

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10
Q

What are some drug interactions for class IB drugs?

A
  • drugs that interfere with CYP3A4 (e.g. cimetidine)
  • drugs metabolized by CYP1A2 (Mexiletine potently inhibits 1A2)
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11
Q

What are 2 class IC drugs?

A

Flecainide and propafenone

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12
Q

What are the direct effects of class IC drugs?

A
  • increased AP threshold
    • few/variable effects on AP duration/ERP
  • decreased Vmax (conduction velocity)
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13
Q

What are some side effects of class IC drugs?

A
  • pro-arrhythmic (increased incidence of malignant arrhythmias and mortality)
  • negative inotropic effect (can worsen heart failure)
  • dizziness, nausea
  • bradycardia (propafenone inhibits Ca channel and beta receptors)
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14
Q

When are class IC drugs used?

A

Only approved in life threatening situations when SVT/ventricular arrhythmias are resistant to other drugs (because of pro-arrhythmic side effects)

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15
Q

What are some drug interactions for class IC drugs?

A
  • drugs that inhibit CYP2D6… e.g:
    • bupropion (antidepressant)
    • ritonavir (antiretroviral)
    • terbinafine (antifungal)
    • cimetidine (H2 antagonist)
    • amiodarone (antiarrhythmic drug)
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16
Q

What are 3 class II drugs?

A

Propranolol, esmolol, metoprolol

17
Q

What are the direct effects of class II drugs?

A

**Beta blockers

  • bind beta adrenergic receptors on cardiac cell membranes to competitively inhibit epi/NE binding
  • antagonize effects of sympathetic stimulation (slow rate of diastolic/phase 4 depolarization)
18
Q

When are class II drugs used?

A
  • all atrial arrhythmias
  • ventricular tachycardia and fibrillation

**B blockers are currently the most useful antiarrhythmic drugs available due to their safety (don’t prolong AP; safe in long QT syndrome) and wide clinical applications

19
Q

What are some side effects of class II drugs?

A
  • negative inotropic effect
  • heart block
  • bradycardia
  • bronchospasm
20
Q

What are 3 class III drugs?

A

Amiodarone, sotalol, and dofetilide

21
Q

What are the direct effects of class III drugs?

A
  • main common property= K channel blockers
    • prolongs repolarization
    • most common target= IKr (hERG channel)… can result in aquired long QT syndrome
    • reverse use-dependent (more effective at a slower heart rate)
  • ultimately increase ERP
22
Q

What are the effects of amiodarone? What is it commonly used for?

A
  • Major action= K channel blocker (both IKr and IKs)
  • modest Na channel blocker
  • modest Ca channel blocker
  • modest beta-adrenoreceptor blocker

**effective against v tach/fib and to prevent recurrent atrial fib/flutter

23
Q

What are some common side effects of amiodarone?

A
  • triggered arrhythmias (from EADs) **Rarely associated with Torsades!
  • hypothyroidism
  • pulmonary fibrosis
  • hepatotoxicity
24
Q

What are some drug interactions with amiodarone?

A

Inhibits P450s, dectreasing clearance of:

  • warfarin
  • digoxin
  • quinidine
  • flecainide
  • sildenafil (PDE5 inh)
  • simvastatin
25
Q

What are the effects of sotalol? What is it commonly used for?

A
  • major action= K channel blocker (IKr)
  • secondary action= beta blocker

**effective against V tach/fib, SVTs, and atrial fibrillation

26
Q

What are some common side effects of sotalol?

A
  • most serious= triggered arrhythmias with Torsades de pointes
  • fatigue
  • bradycardia
27
Q

What are some drug interactions with sotalol?

A

**Use with caution in conjunction with other drugs that prolong QT (e.g. class IA antiarrthmics, tricyclic antidepressants, and quinolong antibiotics)

28
Q

What are the effects of dofetilide? What is it commonly used for?

A
  • major action= K channel blocker (IKr)

**effective against atrial fibrillation and flutter (not hepatotoxic like amiodarone and safe for patients with L ventricular dysfunction)

29
Q

What are some common side effects of dofetilide?

A
  • most serious= triggered arrhythmias (torsades de pointes!)…. requires careful monitoring
  • headache
  • dizziness
  • chest pain
30
Q

What are some drug interactions with dofetilide?

A
  • drugs that interfere with renal secretion (dofetilide is eliminated via the kidney)
  • drugs that inhibit CYP3A4 (e.g. cimetidine)
31
Q

What are 2 class IV drugs?

A

Diltiazem (benzothiazepines) and Verapamil (phenylalkylamines)

**Dihydropyridines NOT used for arrhythmias (they mainly target the vasculature, used for angina)

32
Q

What are the effects of class IV drugs? What are they commonly used for?

A
  • Ca channel blockers **act primarily on slow response cells (SA/AV node) which are dependent on Ca influx for AP depolarization
    • increase AP threshold
    • increase nodal cell refractory period
    • depress conduction velocity in the SA and AV nodes

**commonly used for SVT (rarely for v tach!)

33
Q

What are some common side effects of class IV drugs?

A
  • negative chronotropic effect (decreases automaticity of SA node)
  • negative inotropic effect (decreases Ca influx during plateau phase of ventricular AP)
  • hypotension (decreased Ca inlfux into vascular smooth mucle)
  • nifedipine= peripheral edema
  • verapamil= constipation
  • verapamil and diltiazem=
    • interacts with digitalis -> slowed AV conduction -> heart block
    • increase plasma digitalis (competes for renal excretion)
34
Q

What are some drug interactions with class IV drugs?

A

Diltiazem and verapamil are moderate inhibitors of CYP3A4, reducing clearance of quinidine, digoxin, simvastatin

35
Q

Describe the effects of adenosine

A
  • very rapidly activates K channels to slow depolarization at the AV node
  • blocks cAMP enhanced Ca channel activity
  • indicated for SVT (slows AV conduction and HR)
36
Q

Describe the effects of digoxin

A
  • aka digitalis glycoside
  • enhances vagal parasympathetic activity to slow conduction at the AV node
  • indicated for A fib and SVT to control ventricular response rate
37
Q

Describe the effects of ranolazine

A
  • blocks persistent Na channel current (reducing excitability) and IKr
  • prolongs QT interval
  • used for treatment of chronic angina
38
Q

Describe the effects of ivabradine

A
  • inhibits the pacemaker funny current If
  • prolongs diastolic depolarization and slows SA node firing -> reduces HR
39
Q

Summarize when you would use different antiarrhythmic drugs

A
  • IA for all arrhythmias (SVT, premature ventricular contraction, V tach, some effect on A fib)
    • quinidine, procainamide, disopyramide
  • IB for premature ventricular contractions and V tach
    • lidocaine and mexiletine
  • IC for premature ventricular contractions and V tach (some effect on SVT)
    • flecainide, propagenone
  • II and III for all arrhythmias
    • propranolol, amiodarone, sotalol
  • IV for SVT (some effect on A fib) **nodal effects, don’t help ventricular arrhythmias
  • Digitalis for SVT and A fib
  • Adenosine for SVT

Cardio CP1 (16 decks)

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