Medications Used to Treat Dysrhythmias

Electrical Conduction System of the Heart

  • Cardiac muscle exhibits autorhythmicity, generating electrical impulses autonomously.

  • Electrical impulses enable coordinated contractions of atria and ventricles.

Components of the Heart's Electrical System

  • Sinoatrial (SA) Node: Pacemaker of the heart in the right atrium; initiates electrical impulse.

  • Atrioventricular (AV) Node: Receives impulse from SA node; introduces a delay allowing atrial contraction before ventricle contraction.

  • Bundle of His and Bundle Branches: Conduct impulses from AV node to ventricles.

  • Purkinje Fibers: Spread impulses rapidly throughout the ventricles for simultaneous contraction.

Electrocardiogram (ECG) Components

  • P Wave: Atrial depolarization.

  • QRS Complex: Ventricular depolarization.

  • T Wave: Ventricular repolarization.

Dysrhythmias

  • Altered heart rhythms that affect blood ejection and oxygen delivery.

  • Treated with medications or invasive procedures.

Antidysrhythmic Medications Classification (Vaughan Williams Classification)

Class I: Sodium Channel Blockers

  • Mechanism: Inhibit sodium channels; slow depolarization.

  • Uses: Atrial fibrillation, ventricular dysrhythmias.

  • Adverse Effects: Allergic reactions, nausea, dizziness.

  • Examples: Procainamide, Lidocaine, Propafenone.

Class II: Beta Blockers

  • Mechanism: Decrease heart muscle stimulation; slow AV conduction.

  • Uses: Myocardial infarction, hypertension.

  • Adverse Effects: Decreased heart rate, fatigue.

  • Examples: Atenolol, Propranolol.

Class III: Potassium Channel Blockers

  • Mechanism: Prolongs action potential duration.

  • Uses: Atrial fibrillation, life-threatening ventricular dysrhythmias.

  • Adverse Effects: Dizziness, low heart rate.

  • Examples: Amiodarone, Sotalol.

Class IV: Calcium Channel Blockers

  • Mechanism: Block calcium channels; prolong action potential.

  • Uses: Hypertension, rate regulation in atrial fibrillation.

  • Adverse Effects: Constipation, dizziness.

  • Examples: Diltiazem, Verapamil.

Miscellaneous Class

  • Adenosine: Used in emergencies for fatal dysrhythmias; slows conduction through AV node. Adverse effects include shortness of breath and chest pain.

Contraindications for Antidysrhythmic Medications

  • History of allergic reactions.

  • Certain dysrhythmias (e.g., 2nd and 3rd-degree heart block).

  • Cardiogenic/septic shock, heart damage post-myocardial infarction.