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  • Supraventricular (atrial) or ventricular in origin: most common causes—enhanced/abnormal automaticity & reentry; goals & roles of drug therapy vary by arrhythmia
  • Atrial arrhythmias: sinus bradycardia, sinus tachycardia, premature atrial contractions (PACs), paroxysmal supraventricular tachycardia (PSVT), Wolff-Parkinson-White (WPW) syndrome, atrial flutter, atrial fibrillation (AF)
  • Ventricular arrhythmias: ventricular premature depolarizations (VPDS), ventricular tachycardia (VT), ventricular fibrillation (VF); arrhythmias involved in cardiac arrest in Chapter 5 Advanced Cardiac Life Support (ACLS)

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Antiarrhythmic Medications

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Class I: Na+ Channel Blockers

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  • Class IA: disopyramide, procainamide, quinidine; prolong action potential, ↑ refractory period; prolongs QTc interval by inhibiting K+ channels (↑ risk for torsades de pointes [TdP]); monitor ECG & QTc; rarely used in clinical practice except procainamide (LD 20mg/min until arrhythmia controlled, hypotension occurs, QRS widens by 50% or total of 17mg/kg; max infusion 1–4mg/min); mainly used for ventricular arrhythmias, avoid in structural heart disease
  • Class IB: lidocaine, mexiletine (rarely used); shortens action potential & refractory period; use for ventricular arrhythmias; lidocaine only recommended for VF when amiodarone unavailable
  • Class IC: flecainide, propafenone; variable effects on action potential, minimal effect on refractory period; usually used in AF; avoid in patients with structural heart disease

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Class II: β-Blockers

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↓ HR, inhibits sinus node by ↓ adrenergic tone, also ↓ HR in AF by blocking AV node (rate control); may cause bradycardia &/or heart block; bisoprolol, carvedilol, or metoprolol succinate should be used in concomitant HF (J Card Fail 2010;16:475)

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Class III: K+ Channel Blockers

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Amiodarone, dofetilide, dronedarone, ibutilide, sotalol; prolongs refractory period; prolongs QTc interval (↑ risk of TdP); monitor ECG & QTc; used more than Class I agents

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  • Amiodarone: most important antiarrhythmic, commonly used for supraventricular arrhythmias & to ↓ frequency of shocks in patient with implantable cardioverter defibrillators (ICDs); blocks Na+ & Ca2+ channels & has β-blocking in addition to K+ channel blocking
  • Dofetilide: only prescribed by certified prescribers; initiation, reinitiation, or dose ↑ of dofetilide requires hospitalization of at least 3d to assess QTc prolongation through continuous ECG monitoring & renal function; ↑ risk of TdP; only treats AF
  • Dronedarone: structural analogue of amiodarone; maintains sinus rhythm for patients in AF; does not convert to sinus rhythm (do not use for chemical cardioversion); most common side effects(N/V/D, ↑ SCr, hepatotoxicity & liver failure needing transplantation); less effective than amiodarone but less likely to have thyroid, pulmonary, skin AEs; ↑ QTc but low risk for TdP alone; contraindicated in patients with class III or IV HF or recent hospitalization for decompensated heart failure;avoid use in patients with permanent AF (N Engl J Med 2011;365:2268)
  • Ibutilide: used for cardioversion of AF w/in few weeks after onset; more effective in converting atrial flutter than AF; effects w/in 1h of administration; resuscitation equipment needs to be available during administration due to risk of TdP (women at > risk than men); avoid ...

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