Drugs for Dysrhythmias

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Drugs for Dysrhythmias

• Chapter 26

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Dysrhythmias

• What is a dysrhythmia?
• Why is dysrhythmia a better term than the
  previously used arrhythmia?
• Describe the range of symptoms associated with
  dysrhythmias.
• Discuss the typical symptoms.
• Identify the underlying cause of the symptoms.

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Dysrhythmias

• Why is it essential to terminate/control
  dysrhythmias?
• What is the most common dysrhythmia?
• Why are ventricular dysrhythmias generally more
  serious?

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Dysrhythmias

• Most often classified by type of rhythm
  abnormality and location where it is produced.
• Mary has a regular heart beat of 54 beats per
  minute. Her telemetry monitor shows a normal
  complex configuration. How would this
  dysrhythmia be classified?
• Why is correct diagnosis important?

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Associated Disorders

• Heart disease
• Myocardial infarction
• Hypertension
• Cardiac valve disease
• e.g., mitral stenosis
• CAD

• Medications
• e.g., digoxin
• Hypokalemia
• Stroke
• Diabetes mellitus
• Heart Failure

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Impulse Conduction

• What is the importance of the action potential?
• What is the purpose of the conduction system?
• How long does it take an impulse to travel ?
• Discuss synchronization.

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Conduction Abnormalities

• Mary tells the nurse she feels like her heart
  skips a beat ever so often. Two nurses check
  the apical pulse against the radial pulse and
  find a difference of 4 beats per minute. The
  telemetry monitor occasionally has a complex that
  looks different from the rest.
• What is this difference in pulses called?
• What is the reason for the difference?

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Nonpharmacologic Interventions

• Cardioversion
• Difibrillation
• Catheter ablation
• Implanted pacemaker
• Implanted cardioverter defibrillator

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Antidysrhythmic Pharmacotherapy

• Goals
• Terminate existing dysrhythmias
• Prevention of abnormal rhythms
• Guiding principle
• Pharmacotherapy should generally be used for
  patients with overt symptoms or conditions not
  controlled by other means

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Action Potentials

• AP is initiated when cell membrane Na channels
  open and Na rushes into the cell ? rapid
  depolarization. Ca enters the cell through
  Ca channels and the influx of Ca triggers
  release of intracellular Ca ? a lot of Ca
  available for myocardial muscle contraction.

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Action Potentials

• During depolarization inside of plasma membrane
  becomes positively charged. Na/K pump is
  activated and Na is moved out of cell and K is
  moved back in through respective channels.
• How is this process important to cardiac
  pharmacology?

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Antidysrhythmics

• Mechanism of Action
• Alter specific electrophysiologic properties of
  the heart
• Accomplished by
• Blocking flow through ion channels
• Altering autonomic activity

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Antidysrhythmic Classifications

• Class I Na Channel Blockers
• Class II Beta-Adrenergic Blockers
• Class III K Channel Blockers
• Class IV Ca Channel Blockers
• Class V Miscellaneous

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Sodium Channel Blockers

• Prototype procainamide (Pronestyl) p. 368
• 3 subclasses based on differences in MOA
• Prevents depolarization ? slowed impulse
  conduction and suppresses ectopic foci
• Similar to anesthetic agents
• Side effects vary by drug
• What side effects would you expect?

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Sodium Channel Blockers

• Quinidine and procainamide effective for many
  dysrhythmias
• Other drugs in class reserved for
  life-threatening dysrhythmias
• Lidocaine can cause CNS toxicity.
• What signs would indicate this?
• Some drugs in class also exert an anticholinergic
  effect.
• What signs would indicate this?

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NCs Sodium Channel Blockers

• Complete health hx and physical exam
• Baseline ECG, VS, LFTs, RFTs, e-lytes
• Contraindications HF, ? BP, MG, Renal or Hepatic
  impairment
• Drug-Drug interactions
• Monitor ECG
• Frequent BP
• Monitor for change in LOC, respiratory status
• Drug plasma levels
• Quinidine assess for diarrhea

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Client Teaching Sodium Channel Blockers

• Do not skip dose
• Do not double up if a dose is missed
• No alcohol, caffeine, tobacco
• Keep all scheduled lab appts
• Immediately report
• SOB, signs of bleeding, excessive bruising,
  fever, nausea, persistent headache, vision
  changes, hearing changes, diarrhea, dizziness

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Beta-Adrenergic Blockers

• Widely used
• Decrease HR and conduction velocity ? suppression
  of many dysrhythmias
• Approved acebutolol, esmolol, propranolol
• Avoid-
• heart block, asthma, severe bradycardia,
• Side effects
• Bradycardia, hypotension, dizziness, syncope
• Non-selective beta blockers can cause bronchospasm

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Potassium Channel Blockers

• Prolong duration of action potential and reduce
  automaticity
• Delay repolarization and lengthen refractory
  period ? stabilization of dysrhythmia
• Prototype amiodarone (Cordarone) p. 372
• Limited use due to side effects
• Serious bradycardia and hypotension
• Can worsen dysrhythmias
• Elderly with HF at increase risk of adverse
  cardiac effects

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NCs Potassium Channel Blockers

• Use cautiously in heart block
• Baseline ECG and VS
• Amiodarone baseline CXR, PFTs
• IV RX continuous VS and ECG monitoring
• Withhold if pulse lt 60, SBP lt 90
• Watch for s/s of HF
• Monitor serum levels
• Pregnancy category C or D
• Not recommended during lactation

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Client Teaching Potassium Channel Blockers

• Regular eye exams
• Avoid prolonged sun exposure
• Use sunscreen
• Take with food
• Immediately report
• SOB, palpitations, cough, vision changes, yellow
  sclera, jaundice, RUQ pain, dizziness

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Calcium Channel Blockers

• Widely prescribed for cardiovascular disorders
• Decrease conduction velocity ? stabilization of
  dysrhythmia
• Prototype verapamil (Calan) p. 373
• Dilatizem (Cardizem) and verapamil block calcium
  channels in both heart and arterioles
• Only effective on supraventricular dysrhtymias
• Safe and well tolerated
• Common side effects bradycardia and hypotension
• Increase risk of bradycardia and HP when
  concurrent with betablockers

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Miscellaneous Drugs

• Digoxin indicated for atrial fibrillation
• Monitor closely for toxicity
• Adenosine (Adenocard)
• Only used for Paroxysmal Supraventricular
  Tachycardia
• Naturally occurring nucleoside
• Slows impulse conduction through A-V node and
  decreases automaticity
• Dyspnea common but self-limiting