Updated: 6/14/2021

Antiarrhythmics

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Snapshot
  • A 65-year-old man with atrial fibrillation presents to his primary care physician for a rash. He reports that he recently switched antiarrhythmic medications as instructed by his cardiologist. He reports to having discoloration of his skin and a burning sensation after sun exposure. On physical exam, there are blue and gray discolorations of his skin. An eye exam also reveals yellow-brown granules in the cornea. He was discontinued from the new anti-arrhythmic medication. (Amiodarone photosensitivity)
Introduction
  • Anti-arrhythmic medications are divided into 4 classes
    • Class I drugs are Na+ channel blockers
    • Class II drugs are β-blockers
    • Class III drugs are K+ channel blockers
    • Class IV drugs are Ca2+ channel blockers
Anti-arrhythmics
Class
Drugs Mechanism
Class IA Na+ channel blockers
  • Double Quarter Pounder
    • Disopyramide
    • Quinidine
    • Procainamide
  • ↑ Action potential (AP)
  • ↑ Effective refractory period (ERP)
  • ↑ QT interval
Class IB Na+ channel blockers
  • Lettuce and Mayo
    • Lidocaine
    • Mexiletine
  • ↓ AP
  • ↓ ERP
  • affects ischemic or depolarized tissue
    • hence, great for post-myocardial infarction arrhythmias
Class IC Na+ channel blockers
  • Fries Please 
    • Flecainide
    • Propafenone
  • ↑ ERP in atrioventricular node but not in ventricular tissue 
Class II β-blockers
  • Drug name - lol
  • Selective β-blockers
    • metoprolol, esmolol, propranolol, atenolol, and timolol
    • esmolol is the most short-acting
  • Nonselective α- and β-blockers
    • carvedilol
    • labetalol         
  • ↓ Sinoatrial and atrioventricular nodal activity
    • ↓ cAMP and ↓ Ca2+ currents
    • ↓ slope of phase 4
  • ↑ PR interval
Class III K+ channel blockers
  • AIDS  
    • Amiodarone
    • Ibutilide
    • Dofetilide
    • Sotalol
  • ↑ AP 
  • ↑ ERP 
  • ↑ QT interval
Class IV Ca2+ channel blockers
  • Class IV Drugs
    • Verapamil
    • Diltiazem
  • ↑ ERP
  • ↑ PR interval
  • ↓ Conduction velocity 
 
Class I - Na+ Channel Blockers
  • These drugs slow down conduction and ↓ slope of phase 0 depolarization
  • Class IA (disopyramide, quinidine, and procainamide)
    • clinical use
      • atrial and ventricular arrhythmias
        • re-entrant and ectopic supraventricular tachycardias (SVTs) and ventricular tachycardias (VTs)
    • toxicity
      • thrombocytopenia
      • torsades de pointes
        • from ↑ QT interval
      • heart failure (disopyramide)
      • headache (quinidine)
      • tinnitus (quinidine)
      • reversible systemic lupus erythematosus-like syndrome (procainamide)
  • Class IB (lidocaine and mexiletine)
    • clinical use
      • post-myocardial infarction and other ventricular arrhythmias
      • digitalis-induced arrhythmias
    • toxicity
      • cardiovascular depression 
      • central nervous system effects
  • Class IC (flecainide and propafenone)
    • clinical use
      • SVTs, including atrial fibrillation
    • toxicity
      • proarrhythmic
      • contraindicated in structural and ischemic heart disease, especially post-myocardial infarction
Class II - β-Blockers
  • Clinical use
    • SVTs, including atrial fibrillation and atrial flutter
  • Toxicity
    • impotence
    • exacerbation of lung disease (chronic obstructive pulmonary disease and asthma)
    • cardiovascular effects
      • bradycardia
      • atrioventricular block
      • heart failure
    • central nervous system effects
      • sedation
      • sleep disturbance
    • dyslipidemia (metoprolol)
    • exacerbate Prinzmetal angina (propranolol)
  • Treatment for an overdose of β-blockers
    • saline
    • atropine
    • glucagon
Class III - K+ Channel Blockers
  • Clinical use
    • atrial fibrillation
    • atrial flutter
    • VT
      • especially amiodarone and sotalol
  • Toxicity 
    • torsades de pointes (sotalol and ibutilide) 
    • excessive β-blockade (sotalol)
    • amiodarone
      • no risk of torsades de pointes
      • check pulmonary function tests (PFTs), liver function tests (LFTs), and thyroid function tests (TFTs)
        • pulmonary fibrosis 
        • hepatotoxicity
        • thyrotoxicity
      • blue/gray skin deposits and photodermatitis
      • corneal deposits
      • neurologic effects
      • gastrointestinal effects
      • cardiovascular depression
        • bradycardia
        • heart block
        • heart failure
Class IV - Ca2+ Channel Blockers
  •  Clinical use
    • atrial fibrillation
    • prevention of SVT
  • Toxicity
    • constipation
    • flushing
    • edema
    • cardiovascular depression
      • heart failure
      • atrioventricular block
      • sinus node depression
Other Anti-Arrhythmics
  • Adenosine
    • mechanism
      • ↑ K+ out of cells causes hyperpolarization of the cell and decreased atrioventricular node conduction
      • very short-acting (approximately 15 seconds)
    • clinical use
      • diagnosing and/or terminating SVT
    • toxicity
      • flushing
      • hypotension
      • chest pain
      • sense of impending doom
      • bronchospasm
  • Mg2+
    • clinical use
      • torsades de pointes
      • digoxin toxicity
    • toxicity
      • lethargy
      • bradycardia

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