Download Pharmacology and the Nursing Process, 4th ed. Lilley/Harrington

Chapter 25
Antidysrhythmic Drugs
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Antidysrhythmics
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Dysrhythmia
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
Any deviation from the normal rhythm of the heart
Antidysrhythmics
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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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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
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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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Action Potential (cont’d)

Four phases
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The SA node and the Purkinje cells each have
separate action potentials
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Action Potential Duration
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Absolute or effective refractory period
Relative refractory period
Threshold potential

Automaticity or pacemaker activity
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Electrocardiography
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ECG or EKG
P wave
PR interval
QRS complex
ST segment
T wave
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Common Dysrhythmias
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Supraventricular dysrhythmias
Ventricular dysrhythmias
Ectopic foci
Conduction blocks
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Vaughan Williams Classification
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
System commonly used to classify
antidysrhythmic drugs
Based on the electrophysiologic effect of
particular drugs on the action potential
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Vaughan Williams
Classification (cont’d)
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Class I
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Class Ia
Class Ib
Class Ic
Class II
Class III
Class IV
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Vaughan Williams Classification:
Mechanism of Action
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Class I
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

Membrane-stabilizing drugs
Fast sodium channel blockers
Divided into Ia, Ib, and Ic drugs, according
to effects
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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)
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Class Ib: phenytoin, lidocaine
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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
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Block sodium channels (more pronounced effect)
Little effect on APD or repolarization
Used for severe ventricular dysrhythmias
May be used in atrial fibrillation/flutter, WolffParkinson-White syndrome, supraventricular
tachycardia dysrhythmias
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Vaughan Williams Classification:
Mechanism of Action and
Indications (cont’d)
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Class II: beta blockers: atenolol, esmolol,
metaprolol
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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)
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Class III: amiodarone, dronedarone,
dofetilide, sotalol*, ibutilide
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
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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)
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Class IV: verapamil, diltiazem
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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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Unclassified Antidysrhythmic
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adenosine (Adenocard)
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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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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?
A. Check the patient’s pulse.
B. Prepare to administer CPR.
C. Set up for defibrillation.
D. Continue to monitor the patient.
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Antidysrhythmics:
Adverse Effects
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ALL antidysrhythmics can cause
dysrhythmias!
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Hypersensitivity reactions
 Nausea
 Vomiting
 Diarrhea
 Dizziness
 Blurred vision
 Headache
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Nursing Implications
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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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Nursing Implications (cont’d)
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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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Nursing Implications (cont’d)
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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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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?
A. Assess the patient for diaphoresis.
B. Check the IV lock to see if it is functioning properly.
C. Repeat the dose of diltiazem (Cardizem)
D. Restart the IV in another location.
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Nursing Implications (cont’d)
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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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Classroom Response Question
A patient is receiving oral quinidine. Which
assessment finding is of most concern?
A. Nausea
B. Prolonged QT interval
C. Diarrhea
D. Occasional palpitations
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Nursing Implications (cont’d)
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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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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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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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Nursing Implications (cont’d)
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Monitor for therapeutic response
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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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