Antidysrhythmic Drugs

Pharmacology >> Antidysrhythmic Drugs

Overview

Antidysrhythmic drugs are used to treat dysrthythmias, which is any deviation from the normal rhythm of the heart. 

Mechanism of Action

Antidysrhythmic drugs work by correcting abnormal cardiac function.  There are four classes of antidysrhytmics which each have a different mechanism of action. 

  • Class I drugs work on sodium channels, and are subdivided in a, b, and c classes. 
  • Class II drugs are beta-adrenergic blockers also called beta-blockers.  These work by reducing or blocking sympathetic nervous system stimulation to the heart and thus reducing or blocking the transmission of impulses within the heart’s impulse conduction system. 
  • Class III drugs increase the APD by prlonging repolarization. 
  • Class IV drugs are calcium channel blockers which inhibit the calcium channels reducing the movement of calcium ions in the cells during action potentials. 

Indications

They are used to treat dysrhythmias, and some classes are also used in the treatment of angina and hypertension.

Contraindictions

Include known drug allergies, as well as second or third-degree AV block, a bundle branch block, cardiogenic shock, sick sinus syndrome, and other major ECG changes.

Adverse Effects

Common adverse effects include hypersensitivity reactions, nausea, vomiting, diarrhea, dizziness, headache and blurred vision.  Some antidysrhythmics are able to cause to dysrhythmias. 
Toxicity
Another adverse effect is drug toxicity.  The main toxic effect of antidysrhythmic drugs involve the heart, circulation and CNS. 

Interactions

Are unique to each individual drug but can include the potentiation of anticoagulent activity with warfarin (coumadin).

Drugs

Class Ia; Sodium Channel Blockers
Examples

  • Procainamide (Pronestyl, Procanbid)
  • Quinidine Sulfate (Quinidex Extentabs)
  • Disopyramide (Norpace)
  • Tocainide (Tonocard)
  • Propafenone (Rythmol)

Expected Pharmacological Action

  • Decrease electrical conduction)
  • Increase automaticity)
  • Decrease rate of repolarization)

Therapeutic Uses

  • Supraventricular tachycardia
  • Ventricular tachycardia
  • Atrial flutter
  • Atrial fibrillation

Class Ib; Sodium Channel Blocker
Examples

  • Lidocaine (Xylocaine)

Expected Pharmacological Action

  • Decrease electrical conduction
  • Decrease automaticity
  • Increase rate of repolarization

Therapeutic Uses

  • Short-term use for ventricular dysrhythmias

Class IV; Calcium Channel Blockers
Examples

  • Verapamil (Calan)
  • Diltiazem (Cardizem)

Expected Pharmacologic Action

  • Decrease force of contraction
  • Decrease heart rate
  • Slowing or the rate of conduction through the AV node

Therapeutic Uses

  • Atrial fibrillation and flutter
  • SVT

References

Medication Classification: Antidysrhythmic Medications. (2008). Pharmacology for nursing ver. 4.2. Assessment Technologies Institute, LLC.

Lilley, L., Harrington, S., & Snyder, J.  Antidysrhythmic Drugs. (2007). Pharmacology and the nursing process 5th ed. Canada: Mosby Elsevier.

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