1. Antidysrhythmic Drugs
Chapter 25
Antidysrhythmic Drugs
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Antidysrhythmics
Dysrhythmia
Any deviation from the normal rhythm of the heart
Antidysrhythmics
Used for the treatment and prevention of disturbances in cardiac rhythm
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Cardiac Cell
Inside the resting cardiac cell there is a net negative charge relative to the outside of the cell
This difference in electronegative charge results from an uneven distribution of ions (sodium, potassium, calcium) across the cell membrane
Resting membrane potential (RMP)
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4. Resting Membrane Potential (RMP)
An energy-requiring pump is needed to maintain this uneven distribution of ions
Sodium-potassium ATPase pump
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Action Potential
A change in the distribution of ions causes cardiac cells to become excited
The movement of ions across the cardiac cell’s membrane results in an electrical impulse spreading across the cardiac cells
This electrical impulse leads to contraction of the myocardial muscle
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6. Action Potential (cont’d)
Four phases
The SA node and the Purkinje cells each have separate action potentials
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10. Action Potential Duration
Absolute or effective refractory period
Relative refractory period
Threshold potential
Automaticity or pacemaker activity
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Electrocardiography
ECG or EKG
P wave
PR interval
QRS complex
ST segment
T wave
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Common Dysrhythmias
Supraventricular dysrhythmias
Ventricular dysrhythmias
Ectopic foci
Conduction blocks
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15. Vaughan Williams Classification
System commonly used to classify antidysrhythmic drugs
Based on the electrophysiologic effect of particular drugs on the action potential
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16. Vaughan Williams Classification (cont’d)
Class Ia
Class Ib
Class Ic
Class II
Class III
Class IV
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17. Vaughan Williams Classification: Mechanism of Action
Membrane-stabilizing drugs
Fast sodium channel blockers
Divided into Ia, Ib, and Ic drugs, according to effects
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18. Vaughan Williams Classification: Mechanism of Action and Indications
Class Ia: quinidine, procainamide, disopyramide
Block sodium (fast) channels
Delay repolarization
Increase APD
Used for atrial fibrillation, premature atrial contractions, premature ventricular contractions, ventricular tachycardia, Wolff-Parkinson-White syndrome
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Vaughan Williams Classification: Mechanism of Action and Indications (cont’d)
Class Ib: phenytoin, lidocaine
Block sodium channels
Accelerate repolarization
Increase or decrease APD
Lidocaine is used for ventricular dysrhythmias only
Phenytoin is used for atrial and ventricular tachydysrhythmias caused by digitalis toxicity, long QT syndrome
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Vaughan Williams Classification: Mechanism of Action and Indications (cont’d)
Class Ic: flecainide, propafenone
Block sodium channels (more pronounced effect)
Little effect on APD or repolarization
Used for severe ventricular dysrhythmias
May be used in atrial fibrillation/flutter, Wolff-Parkinson-White syndrome, supraventricular tachycardia dysrhythmias
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Vaughan Williams Classification: Mechanism of Action and Indications (cont’d)
Class II: beta blockers: atenolol, esmolol, metaprolol
Reduce or block sympathetic nervous system stimulation, thus reducing transmission of impulses in the heart’s conduction system
Depress phase 4 depolarization
General myocardial depressants for both supraventricular and ventricular dysrhythmias
Also used as antianginal and antihypertensive drugs
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Vaughan Williams Classification: Mechanism of Action and Indications (cont’d)
Class III: amiodarone, dronedarone, dofetilide, sotalol*, ibutilide
Increase APD
Prolong repolarization in phase 3
Used for dysrhythmias that are difficult to treat
Life-threatening ventricular tachycardia or fibrillation, atrial fibrillation or flutter that is resistant to other drugs
*Sotalol also exhibits Class II properties
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Vaughan Williams Classification: Mechanism of Action and Indications (cont’d)
Class IV: verapamil, diltiazem
Calcium channel blockers
Inhibit slow-channel (calcium-dependent) pathways
Depress phase 4 depolarization
Reduce AV node conduction
Used for paroxysmal supraventricular tachycardia; rate control for atrial fibrillation and flutter
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24. Unclassified Antidysrhythmic
adenosine (Adenocard)
Slows conduction through the AV node
Used to convert paroxysmal supraventricular tachycardia to sinus rhythm
Very short half-life—less than 10 seconds
Only administered as fast IV push
May cause asystole for a few seconds
Other adverse effects minimal
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25. Classroom Response Question
A patient has received an IV dose of adenosine, and almost immediately the heart monitor shows asystole. What should the nurse do next?
Check the patient’s pulse.
Prepare to administer CPR.
Set up for defibrillation.
Continue to monitor the patient.
Correct answer: D
Rationale: The half-life of adenosine is very fast—only 10 seconds, and the asystole only lasts for a few seconds. The nurse should continue to monitor the patient for therapeutic and adverse effects of the medication.
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26. Antidysrhythmics: Adverse Effects
ALL antidysrhythmics can cause dysrhythmias!
Hypersensitivity reactions
Nausea
Vomiting
Diarrhea
Dizziness
Blurred vision
Headache
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Nursing Implications
Obtain a thorough drug and medical history
Measure baseline BP, P, I&O, and cardiac rhythm
Measure serum potassium levels before initiating therapy
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28. Nursing Implications (cont’d)
Assess for conditions that may be contraindications for use of specific drugs
Assess for potential drug interactions
Instruct patients to report dosing schedules and adverse effects to physician
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29. Nursing Implications (cont’d)
During therapy, monitor cardiac rhythm, heart rate, BP, general well-being, skin color, temperature, heart and lung sounds
Assess plasma drug levels as indicated
Monitor for toxic effects
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30. Classroom Response Question
A patient is in the emergency department with an unspecified supraventricular dysrhythmia. The physician orders a dose of diltiazem (Cardizem) IV push. While the nurse administers the medication through the IV lock, the patient states she feels something wet spilling on her arm. Her heart rate was unchanged. What will the nurse do next?
Assess the patient for diaphoresis.
Check the IV lock to see if it is functioning properly.
Repeat the dose of diltiazem (Cardizem)
Restart the IV in another location.
Correct answer: B
Rationale: Since the heart rate was unchanged and the patient felt fluid on her arm, the IV lock is probably not working properly. Before anything else is done, the IV lock should be checked for proper functioning. Another dose would be wasted if the IV lock is not working.
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31. Nursing Implications (cont’d)
Instruct patients to take medications as scheduled and not to skip doses or double up for missed doses
Instruct patients to contact their physician for instructions if a dose is missed
Instruct patients not to crush or chew oral sustained-release preparations
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32. Classroom Response Question
A patient is receiving oral quinidine. Which assessment finding is of most concern?
Nausea
Prolonged QT interval
Diarrhea
Occasional palpitations
Correct answer: B
Rationale: Patients on quinidine need to be monitored for prolonged QRS or QT intervals, which may be a precursor to more serious dysrhythmia problems.
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33. Nursing Implications (cont’d)
Monitor ECG for prolonged QT interval with use of antidysrhythmics, including amiodarone, procainamide, quinidine, dofetilide, bepridil, sotalol, flecainide
Administer IV infusions with an IV pump
Solutions of lidocaine that contain epinephrine should not be given IV—they are to be used ONLY as local anesthetics
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34. Nursing Implications (cont’d)
Ensure that the patient knows to notify health care provider of any worsening of dysrhythmia or toxic effects
Shortness of breath
Edema
Dizziness
Syncope
Chest pain
GI distress
Blurred vision
Edema
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35. Nursing Implications (cont’d)
Teach patients taking beta blockers, digoxin, and other drugs how to take their own radial pulse for 1 full minute, and to notify their physician if the pulse is less than 60 beats/minute before taking the next dose
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36. Nursing Implications (cont’d)
Monitor for therapeutic response
Decreased BP in hypertensive patients
Decreased edema
Decreased fatigue
Regular pulse rate
Pulse rate without major irregularities
Improved regularity of rhythm
Improved cardiac output
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