chapter 25 antidysrhythmic drugs copyright © 2014 by mosby, an imprint of elsevier inc
TRANSCRIPT
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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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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