Antiarrhythmics

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

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

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

Other Anti-Arrhythmics

Anti-arrhythmics
Class	Drugs	Mechanism
Class IA Na⁺ channel blockers	Double Quarter PounderDisopyramideQuinidineProcainamide	↑ Action potential (AP)↑ Effective refractory period (ERP)↑ QT interval
Class IB Na⁺ channel blockers	Lettuce and MayoLidocaineMexiletine	↓ AP ↓ ERP affects ischemic or depolarized tissue hence, great for post-myocardial infarction arrhythmias
Class IC Na⁺ channel blockers	Fries Please FlecainidePropafenone	↑ ERP in atrioventricular node but not in ventricular tissue
Class II β-blockers	Drug name – lolSelective β-blockersmetoprolol, esmolol, propranolol, atenolol, and timololesmolol is the most short-actingNonselective α- and β-blockerscarvedilollabetalol	↓ 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 DrugsVerapamilDiltiazem	↑ ERP ↑ PR interval ↓ Conduction velocity