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 IANa+ channel blockers DoubleQuarterPounder Disopyramide Quinidine Procainamide ↑ Action potential (AP)↑ Effective refractory period (ERP)↑ QT interval Class IBNa+ channel blockers Lettuce and Mayo Lidocaine Mexiletine ↓ AP ↓ ERP affects ischemic or depolarized tissue hence, great for post-myocardial infarction arrhythmias Class ICNa+ 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