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Antidysrhythmic Drugs


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Electrical Conduction System Pathway
SA node → spread thru atria → AV node → bundle of HIS → His-Purkinje system → ventricular contraction
What are cardiac action potentials
Self propagating waves of depolarization and repolarization
Generated by movement of ions into and out of cells
Where do fast potentials occur?
occur in His-Purkinje and atria and ventricular muscle
What are the phases of the fast potentials through the His-Purkinje and atria and ventricular muscle?
Phase 0 - rapid depolarization (response to Na+ influx)
Phase 1 – rapid (but partial) repolarization
Phase 2 – prolonged plateau (Ca++ enters cell)
Phase 3 – rapid repolarization (extrusion of K+)
Phase 4 – membrane potential remains stable or undergoes spontaneous depolarization
Where do slow potentials occur?
occur in cells of SA and AV node
What are the phases of slow potentials through the SA and AV node?
Phase 0 – conduction through AV node (slow influx of Ca++
Phase 1,2, and3 – lack a phase I and Phase 2 and 3 not significant with antidysrhythmic drugs
Phase 4 SA and AV node undergo spontaneous depolarization( ionic basis not understood) supressing phase 4 decreases automaticity in the SA node
Why do dysrhythmias occur?
Disturbance of impulse formation (automaticity)
Disturbance of impulse conduction
Classifications of antidysrhythmic drugs
Class I: Sodium Channel Blockers
Class II: Beta Blockers
Class III: Potassium Channel Blockers
Class IV: Calcium Channel Blockers

All of these drugs can worsen preexisting arrythmias
Common Dysrhythmias and Treatment
Supraventricular Dysrhythmias -
Sustained SVT
Atrial Flutter
Atrial Fibrillation

Ventricular Dysrhythmias -
Sustained Ventricular Tachycardia
Sustained Ventricular Fibrillation
Premature Ventricular Beats
Digoxin Induced Ventricular Dysrhythmias
Torsades de Pointes
Goals of treatment of dysrhythmias
Termination of the dysrhythmia
Long term suppression with drugs
Other treaments of dysrhythmias
Ablation /cardioversion/ defibrillation
What is the prototype agent for Antidysrhythmic Drugs?
What is Quinidine used to treat?
Used to treat supraventricular & ventricular arrhythmias
What are the actions of Quinidine?
Slows impulse conduction by blocking sodium channels
Decreases myocardial excitability, conduction velocity, and contractility
Prevents reentry phenomenon
Indirect anticholinergic effects also occur
What are the contraindications of Quinidine?
digitalis toxicity, heart blocks, hypersensitivity to quinidine (or cinchona derivatives)
Common adverse effects of Quinidine
GI symptoms
Serious adverse effect
arterial embolism
hypotension with IV use
What nursing interventions do you need to take with Quinidine?
take oral forms with food, telemetry & vital sign monitoring/volumetric flow pump with IV administration
What patient teaching do you do with Quinidine?
Instruct pt in signs of embolism
What is a drug in Class IB dysrhythmics?
lidocaine (Xylocaine)
What are the actions of lidocaine (Xylocaine)?
Depresses phase 0 (although not as much as IA drugs)
Suppresses automaticity
Used primarily with ventricular dysrhythmias
What is another drug in Class IB dysrhythmics?
lidocaine (Xylocaine) - Not effective orally; NEVER use preparation with epinepherine intravenously
What are the adverse effects of lidocaine (Xylocaine)?
Most common:
CV system (dysrhythmias and hypotension)
CNS (dizziness/lightheadedness, fatigue, and drowsiness)
Excessive levels can produce confusion and seizures. Monitor ECG continuously and switch to another dysrhythmic as soon as stable.
What are Class IC dysrhythmics?
flecainide (Tambocor) and propafenone (Rythmol): oral agents
What are the actions of Class IC dysrhythmics?
Depress phase 0 considerably
Slight effect on repolarization
Decrease conduction significantly
Use usually limited because of an increased risk of mortality
What Class II dysrhythmics are used?
Beta Blockers – only selected agents are approved for use as antiarrhythmics
What are the actions of beta blockers?
Depress the cardiac action potential to control arrhythmias
Slow the heart rate
Decrease CO
What is the prototype of Class II dysrhythmics and it's contraindications?
propanolol - Contraindicated in sinus bradycardia, pulmonary disease and heart failure
What are Class III dysrhythmic agents?
Potassium Channel Blockers
What is the prototype of Potassium Channel Blockers
amiodarone (Cordarone)
What is the action of amiodarone (Cordarone) and when is it used?
Produces a prolonged phase 3 (repolarization).
Used in life-threatening arrhythmias that have not responded to other drug therapies
examples: recurrent ventricular fibrillation,
recurrent unstable ventricular tachycardia
What further information is needed with amiodarone (Cordarone)
Low dose therapy is common (200mg/day) benefits: LV ejection fraction, exercise tolerance & ventricular arrhythmias in HF pts.
Research based practice: amiodarone is commonly used now in treatment of HF, atrial fibrillation, VT, VF not responsive to defibrillation
What are the adverse effects of amiodarone (Cordarone)?
Common adverse effects
CNS – dizziness, tremor, insomnia
Serious Adverse effects:
Pulmonary toxicity (most common)
Exacerbation of the arrhythmia being treated
Photophobia or blurred vision leading to blindness
hyper or hypothyroidism
Pregnancy Category D
What are Class IV antiarrhythmic drugs?
Calcium Channel Blockers
What is the prototype of Calcium Channel Blockers?
verapamil (Calan)
What are the actions of verapamil (Calan)?
Inhibits movement of calcium ions across the cardiac and arterial muscle cell membranes
Slows conduction
Depresses automaticity
Depresses myocardial contractility,
Dilates coronary arteries and peripheral arterioles
What are the pharmacotherapeutics of verapamil (Calan)?
Control of ventricular rate in chronic atrial flutter or fibrillation
Prophylactically (with digoxin) for repetitive paroxysmal supraventricular tachycardia
Treatment of supraventricular tachyarrhythmias
Common adverse effects verapamil (Calan)?
GI – constipation, nausea
Contraindicated in 2nd & 3rd degree heart blocks, hypotension, severe HF
Elderly patients more sensitive to hypotension
NOT a Ca++ channel blocker, Endogenous nucleotide
What are the actions of Adenosine and therapeutic uses?
Decreases automaticity, conduction velocity at the AV node.
Increases the refractory period at the AV node
Used in treatment of paroxysmal supraventricular tachycardia
Given as rapid IV bolus ONLY, followed by saline flush
Continuous telemetry monitoring
What is the prototype & sole agent of Potassium-removing resin?
sodium Polystyrene Sulfonate (Kayexalate)
What are the actions of sodium Polystyrene Sulfonate (Kayexalate)?
Used to lower serum potassium levels to prevent serious or life-threatening dysrhythmias:
Effective lowering of potassium may take several hours.
Use other agents in patients with severe hyperkalemia, in which a more rapid effect is needed.
How is sodium Polystyrene Sulfonate (Kayexalate) gievn to patients?
Given orally or by enema – give cleansing enema prior to rectal administration
For rapid treatment of hyperkalemia
IV D50/Regular Insulin
IV Sodium Bicarbonate
IV Calcium Gluconate

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