Drugs for Dysrhythmias

1
Drugs for Dysrhythmias

• Chapter 17

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Introduction

• Dysrhythmias are abnormalities of electrical
  conduction or rhythm in the heart.
• Sometimes called arrhythmias, they encompass a
  number of different disorders that range from
  harmless to life threatening.

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Introduction

• Proper diagnosis and optimum pharmacologic
  treatment can significantly affect the frequency
  of dysrhythmias and their consequences.
• Fast Facts pg. 296

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Introduction

• The frequency of dysrhythmias in the population
  is difficult to ascertain because many clients
  experience no symptoms.

5
Introduction

• Dysrhythmias are abnormalities of electrical
  conduction or rhythm in the heart
• Aka arrhythmias
• Can be harmless to life threatening
• Electrocardiogram (ECG/EKG) used to make
  diagnosis
• Persistent dysrhythmias increase risk of stroke
  and heart failure
• Severe dysrhythmias may cause sudden death

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Classified by the Location Type of Rhythm
Produced

• Originate in atria (aka supraventricular)
• Premature atrial contractions (PACs)
• Atrial tachycardia
• Atrial flutter
• Atrial fibrillationmost common

• Originate in ventriclesmore serious
• Premature ventricular contractions (PVCs)more
  serious than PACs
• Ventricular tachycardia
• Ventricular flutter or fibrillationrequire
  immediate treatment

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Classified by the Location Type of Rhythm

• Sinus bradycardia and heart blocks may require
  pacemaker

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Disease Commonly R/T Dysrhythmias

• 1. HTN
• 2. Mitral stenosis
• 3. Coronary artery disease (CAD)
• 4. Medications such as digitalis
• 5. Low serum potassium levels

• 6. Myocardial infarction (MI)
• 7. Adverse effects from antidysrhythmic drug
• 8. Stoke (CVA)
• 9. Diabetes Mellitus (DM)
• 10. Congested heart failure (CHF)

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The Electrical Conduction Pathway

• The electrical conductionpathway in the
  myocardium keeps the heart beating in a
  synchronized manner.
• In all types of dysrhythmias there is a defect in
  the formation or conduction of electrical
  impulses across the myocardium.

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The Electrical Conduction Pathway

• Normal conduction pathway in the heart
• Sinoatrial (SA) node
• Atrioventricular (AV) node
• Atrioventricular bundle (Bundle of His)
• Right and left bundle branches
• Purkinje fibers

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The Electrical Conduction Pathway

• Electrocardiogram (ECG)measures this electrical
  activity.
• Ectopic foci or ectopic pacemakers
• Other areas of the heart start to initiate beats.
• Potential to cause dysrhythmias

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The Electrical Conduction Pathway

• Goal of conduction system is to keep heart beat
  in a regular synchronized manner to maintain
  cardiac output.

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Non-Pharmacologic Therapy

• Non-pharmacologic therapy of certain dysrhythmias
  is often the treatment of choice.
• All antidysrhythmic agents have the ability to
  cause rhythm abnormalities or worsen existing
  ones.

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Non-Pharmacologic Therapy

• Because of this, non-pharmacologic treatment is
  sometimes preferred over drug therapy.
• Dysrhythmias may be corrected using cardioversion
  or catheter ablation.

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Non-Pharmacologic Therapy

• Cardioversion or defibrillation
• Electrical shock to heart
• Used for more serious dysrhythmias
• Catheter ablation
• Identification and destruction of myocardial
  cells responsible for abnormal conduction
• Cardiac pacemaker inserter
• Dysrhthmias that cause heart to beat to slowly
• Implantable cardioverter defibrillation
• Pacing the heart or
• Giving an electrical shock when dysrhthmia
  occurs.

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Changes in Na K Levels

• Changes in sodium and potassium levels generate
  the action potential in myocardial cells.
• Antidysrhthmic drugs affect the action potential
  in myocardial cells.
• They act by blocking sodium, potassium, or
  calcium channels in the cell membranes.

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Classified by Mechanism of Action

• All antidysrhythmic drugs can correct, worsen or
  create new dysrhythmias.
• Class Isodium channel blockers
• Class IIbeta-adrenergic blockers
• Class IIIpotassium channel blockers
• Class IVcalcium channel blockers
• Miscellaneous antidysrhythmic drugs.

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Sodium Channel Blockers

• Sodium channel blockers slow the rate of impulse
  conduction through the heart.
• Largest group of antidysrhythmics
• Block opening of sodium ion channels in membrane
• Drug profile quinidine sulfate (Quinidex) pg. 304.

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Beta-Adrenergic Blockers

• Beta-Adrenergic blockers reduce automaticity as
  well as slow conduction velocity in the heart.
• Used to treat large number of CV diseases.
• Serious side effects few used to treat
  dysrhythmias
• Slow heart heart
• Main valuetreat atrial dysrhthmias r/t heart
  failure
• DPpropranolol (Inderal) 305.

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Potassium Channel Blockers

• Potassium channel blockers prolong the refractory
  period of the heart.
• Prolong duration of action potential
• Restricted use because of serious side effects
• DP amiodarone (Cardarone) pg. 306.

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Calcium Channel Blockers

• Two calcium channel blockers are available as
  antidysrhythmicstable 17.5 pg. 307.
• Widely prescribed for various CV disorders
• Reduce automaticity in SA node and slow impulse
  through AV node.
• Only effective against supraventricular
  dysrhythmias.
• DPverapamil (Calan) pg. 307

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Misc. Drugs

• Digoxin and several other drugs are used for
  specific dysrhythmias but do not act by blocking
  ion channelstable 17.6 pg. 308.

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Misc. Drugs

• Digoxin
• Decrease automaticity of SA node and slows
  conduction through AV node
• Used for certain types of atrial dysrhthmias
• Can produce serious dysrhythmias

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Misc. Drugs

• Adenosine (Adenocard)
• Slows conduction through AV node and decreases
  automaticity of SA node.
• Used to terminate serious atrial tachycardia.
• Side effects self-limiting due to short half-life