Anti-arrhythmic Drugs

Classification

  • Antiarrhythmic drugs can be classified either by their mechanism of action or by what they are commonly used to treat.

ventr AP

Mechanism of Action

  1. Membrane stabilising agents- Sodium channel blockers
    1. Those that act to prolong the action potential (can be used in atrial fibrillation, flutter; supraventricular and ventricular tachyarrhythmias)
      1. examples include procainamide, dispyramide and quinidine
        1. The only which is used in Tayside is disopyramide (rarely used- only with specialist guidance)
    2. Those that act to shorten the action potential (ventricular tachyarrhythmias)
      1. Examples include lidocaine and mexiletine (latter not used in Tayside routinely)
    3. Those that have no effect on action potential but have the greatest reduction in the phase 0 slope (SVT and VT)
      1. Examples include flecainide; propafenone
    4. sodium channel subclass effects
  2. Beta-blockers (mainly used in AF/Flutter and to prevent SVT/VT)
    1. Non-selective (β1 and β2 antagonists)
      1. Propanolol is the most commonly used one
    2. Selective (myocardial β1 antagonist)
      1. bisoprolol
    3. Sotalol
      1. Mixture of non-selective beta-blocker and a class III antiarrhythmic (d-sotalol).
  3. Potassium channel blockers
    1. Act to increase the QT interval- particularly useful in tachycardias involving re-entry phenomenon
    2. Most widely used drugs are amiodarone and sotalol (see above)
      1. NB Amiodarone also has class I, II and IV activity (complex mechanism of action)
    3. delayed repolarization
    4. Side effects of amiodarone include hypothyroidism (resembles thyroxine); corneal micro-deposits; optic neuropathy; deranged LFTs (rarely hepatic impairment e.g. jaundice, hepatomegaly); long-term use can cause blue-grey discolouration of the skin and photosensitivity; peripheral neuropathy; gynaecomastia and interstitial pulmonary fibrosis.
  4. Calcium channel blockers
    1. Dihydropyridines (smooth muscle selective- not used as anti-arrhythmic drugs but used in high blood pressure to increase vasodilation.  Examples include amlodipine; nifedipine)
    2. Non-dihydropyridines
      1. Examples include verapamil (fairly cardioselective- most commonly used for arrhythmias/angina)
      2. Diltiazem is an intermediate and is both rate-limiting and has vascular effects (better for blood pressure)

Other antiarrhythmic drugs

  • Atropine sulphate- increases sinus rate and SA/AV conduction
    • Treatment mainly for bradycardias due to vagal overactivity
    • Also used in the acute setting as part of resuscitation measures
  • Adenosine (IV)- main action is to slow atrioventricular conduction (also decreases rate)
    • Can be used in attempting to halt SVT (particularly where the AV node is involved in re-entry e.g. WPWS)
    • It can also be used to help differentiate AF/flutter from VT
      • AF/flutter will produce a transient AV block
      • In VT, no change will occur
    • Avoid in asthmatics if possible (bronchospasm)
  • Digoxin

See also arrhythmias and their managment

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