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CHAPTER 23
Antidysrhythmic Drugs
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Antidysrhythmics

Dysrhythmia


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



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

The SA node and the Purkinje cells each have
separate action potentials
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Action Potential Duration



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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
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Supraventricular dysrhythmias
Ventricular dysrhythmias
Ectopic foci
Conduction blocks
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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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Vaughan Williams
Classification (cont’d)
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Class I
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

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
Class Ia
Class Ib
Class Ic
Class II
Class III
Class IV
Other
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Vaughan Williams Classification:
Mechanism of Action

Class I



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 I: moricizine
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

General class I drug
Has characteristics of all three subclasses
Used for symptomatic ventricular and
life-threatening dysrhythmias
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Vaughan Williams Classification:
Mechanism of Action and
Indications (cont’d)

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
 Used for ventricular dysrhythmias only
• Premature ventricular contractions, ventricular
tachycardia, ventricular fibrillation
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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)

Class II: beta-blockers: atenolol, esmolol,
metaprolol, propranolol



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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)

Class III: amiodarone, sotalol*, ibutilide,
others
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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—resistant to other drugs
• Sustained ventricular tachycardia
*Sotalol also exhibits Class II properties
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Vaughan Williams Classification:
Mechanism of Action and
Indications (cont’d)

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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Vaughan Williams Classification:
Other Antidysrhythmics

Digoxin, adenosine

Have properties of several classes and are not
placed into one particular class
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Unclassified Antidysrhythmic

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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Antidysrhythmics:
Adverse Effects

ALL antidysrhythmics can cause
dysrhythmias!

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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Nursing Implications (cont’d)
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
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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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Nursing Implications (cont’d)
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
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For class I drugs, monitor ECG for QT
intervals prolonged more than 50%
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)

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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