Chapter 25 Antidysrhythmic Drugs Copyright © 2014 by Mosby, an imprint of Elsevier Inc

Chapter 25

Antidysrhythmic Drugs

Copyright © 2014 by Mosby, an imprint of Elsevier Inc.

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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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

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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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)

Class I Class Ia Class Ib Class Ic

Class II Class III Class IV

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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 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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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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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

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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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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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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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)

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)

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)

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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