11 Antidysrhythmics Upd

Copyright © 2002, 1998, Elsevier Science (USA). All rights reserved.

Antidysrhythmic AgentsAntidysrhythmic Agents


AntidysrhythmicsAntidysrhythmics

DysrhythmiaDysrhythmia

• Any deviation from the normal rhythm of the heartAny deviation from the normal rhythm of the heart


• Drugs used for the treatment and prevention of Drugs used for the treatment and prevention of disturbances in cardiac rhythmdisturbances in cardiac rhythm


Cardiac CellCardiac Cell

• Inside the cardiac cell, there exists a net Inside the cardiac cell, there exists a net negative charge relative to the outside of negative charge relative to the outside of the cell.the cell.


Resting Membrane Potential: RMPResting Membrane Potential: RMP

• This difference in the electronegative charge.This difference in the electronegative charge.

• Results from an uneven distribution of ions Results from an uneven distribution of ions (sodium, potassium, calcium) across the cell (sodium, potassium, calcium) across the cell membrane.membrane.

• An energy-requiring pump is needed to An energy-requiring pump is needed to maintain this uneven distribution of ions.maintain this uneven distribution of ions.

• Sodium-potassium ATPase pumpSodium-potassium ATPase pump


Instructors may wish to insert: Instructors may wish to insert: EIC Image # 61: EIC Image # 61:

Heart and Conduction System Heart and Conduction System

EIC Image # 63: EIC Image # 63:

Resting Membrane Potential Resting Membrane Potential of a Cardiac Cellof a Cardiac Cell


Action PotentialAction Potential

• A change in the distribution of ions causes A change in the distribution of ions causes cardiac cells to become excited.cardiac cells to become excited.

• The movement of ions across the cardiac The movement of ions across the cardiac cell’s membrane results in the propagation cell’s membrane results in the propagation of an electrical impulse.of an electrical impulse.

• This electrical impulse leads to contraction This electrical impulse leads to contraction of the myocardial muscle.of the myocardial muscle.


Action PotentialAction Potential

Four PhasesFour Phases

• The SA node and the Purkinje cells each have The SA node and the Purkinje cells each have separate action potentials.separate action potentials.


Instructors may wish to insert: Instructors may wish to insert: EIC Image # 64: EIC Image # 64:

Action Potentials: Phases (SA Node) Action Potentials: Phases (SA Node)

EIC Image # 65:EIC Image # 65: Action Potentials: Purkinje Fiber Action Potentials: Purkinje Fiber

EIC Image # 66:EIC Image # 66:Action Potentials: IntervalsAction Potentials: Intervals


Vaughan Williams ClassificationVaughan Williams Classification

• System commonly used to classify System commonly used to classify antidysrhythmic drugsantidysrhythmic drugs



• Class 1Class 1

– Class IaClass Ia

– Class IbClass Ib

– Class IcClass Ic

• Class IIClass II

• Class IIIClass III

• Class IVClass IV

• OtherOther



Class IClass I

• Membrane-stabilizing agentsMembrane-stabilizing agents

• Fast sodium channel blockersFast sodium channel blockers

• Divided into Ia, Ib, and Ic agents, according Divided into Ia, Ib, and Ic agents, according to effectsto effects



Class IClass I

moricizinemoricizine

• General Class I agentGeneral Class I agent

• Has characteristics of all three subclassesHas characteristics of all three subclasses

• Used for symptomatic ventricular and life-Used for symptomatic ventricular and life-threatening dysrhythmiasthreatening dysrhythmias



Class IaClass Ia

quinidine, procainamide, disopyramidequinidine, procainamide, disopyramide

• Block sodium channelsBlock sodium channels

• Delay repolarizationDelay repolarization

• Increase the APDIncrease the APD

• Used for atrial fibrillation, premature atrial Used for atrial fibrillation, premature atrial contractions, premature ventricular contractions, contractions, premature ventricular contractions, ventricular tachycardia, Wolff-Parkinson-White ventricular tachycardia, Wolff-Parkinson-White syndromesyndrome



Class IbClass Ib

tocainide, mexiletine, phenytoin, lidocainetocainide, mexiletine, phenytoin, lidocaine

• Block sodium channelsBlock sodium channels

• Accelerate repolarizationAccelerate repolarization

• Decrease the APDDecrease the APD

• Used for ventricular dysrhythmias only Used for ventricular dysrhythmias only (premature ventricular contractions, ventricular (premature ventricular contractions, ventricular tachycardia, ventricular fibrillation)tachycardia, ventricular fibrillation)



Class IcClass Ic

encainide, flecainide, propafenone encainide, flecainide, propafenone

• Block sodium channels (more pronounced effect)Block sodium channels (more pronounced effect)

• Little effect on APD or repolarizationLittle effect on APD or repolarization

• Used for severe ventricular dysrhythmiasUsed for severe ventricular dysrhythmias

• May be used in atrial fibrillation/flutterMay be used in atrial fibrillation/flutter



Class IIClass II

Beta blockers: atenolol, esmolol, petaprolol, Beta blockers: atenolol, esmolol, petaprolol, propranolol propranolol

• Reduce or block sympathetic nervous system Reduce or block sympathetic nervous system stimulation, thus reducing transmission of impulses in stimulation, thus reducing transmission of impulses in the heart’s conduction systemthe heart’s conduction system

• Depress phase 4 depolarizationDepress phase 4 depolarization

• General myocardial depressants for both General myocardial depressants for both supraventricular and ventricular dysrhythmiassupraventricular and ventricular dysrhythmias



Class IIIClass III

amiodarone, bretylium, sotalol, ibutilide amiodarone, bretylium, sotalol, ibutilide

• Increase APDIncrease APD

• Prolong repolarization in phase 3Prolong repolarization in phase 3

• Used for dysrhythmias that are difficult to treatUsed for dysrhythmias that are difficult to treat

• Life-threatening ventricular tachycardia or fibrillation, Life-threatening ventricular tachycardia or fibrillation, atrial fibrillation or flutter—resistant to other drugsatrial fibrillation or flutter—resistant to other drugs

• Sustained ventricular tachycardiaSustained ventricular tachycardia



Class IVClass IV

verapamil, diltiazem verapamil, diltiazem

• Calcium channel blockersCalcium channel blockers

• Depress phase 4 depolarizationDepress phase 4 depolarization

• Used for paroxysmal supraventricular tachycardia; Used for paroxysmal supraventricular tachycardia; rate control for atrial fibrillation and flutterrate control for atrial fibrillation and flutter



Other AntidysrhythmicsOther Antidysrhythmics

digoxin, adenosine digoxin, adenosine

• Have properties of several classes and are not Have properties of several classes and are not placed into one particular classplaced into one particular class



DigoxinDigoxin

• Cardiac glycosideCardiac glycoside

• Inhibits the sodium-potassium ATPase pumpInhibits the sodium-potassium ATPase pump

• Positive inotrope—improves the strength of cardiac Positive inotrope—improves the strength of cardiac contractioncontraction

• Allows more calcium to be available for contractionAllows more calcium to be available for contraction

• Used for CHF and atrial dysrhythmiasUsed for CHF and atrial dysrhythmias

• Monitor potassium levels, drug levels, and Monitor potassium levels, drug levels, and for toxicityfor toxicity



adenosine (Adenocard)adenosine (Adenocard)

• Slows conduction through the AV nodeSlows conduction through the AV node

• Used to convert paroxysmal supraventricular Used to convert paroxysmal supraventricular tachycardia to sinus rhythmtachycardia to sinus rhythm

• Very short half-lifeVery short half-life

• Only administered as fast IV pushOnly administered as fast IV push

• May cause asystole for a few secondsMay cause asystole for a few seconds

• Other side effects minimalOther side effects minimal


Antidysrhythmics: Side EffectsAntidysrhythmics: Side Effects

ALL antidysrhythmics can cause dysrhythmias!!ALL antidysrhythmics can cause dysrhythmias!!

• Hypersensitivity reactionsHypersensitivity reactions

– NauseaNausea

– VomitingVomiting

– DiarrheaDiarrhea

– DizzinessDizziness

– Blurred visionBlurred vision

– HeadacheHeadache


Antidysrhythmics: Antidysrhythmics: Nursing ImplicationsNursing Implications

• Obtain a thorough drug and medical history.Obtain a thorough drug and medical history.

• Measure baseline BP, P, I & O, and Measure baseline BP, P, I & O, and cardiac rhythm.cardiac rhythm.

• Measure serum potassium levels before Measure serum potassium levels before initiating therapy.initiating therapy.



• Assess for conditions that may be Assess for conditions that may be contraindications for use of specific agents.contraindications for use of specific agents.

• Assess for potential drug interactions.Assess for potential drug interactions.

• Instruct patients regarding dosing schedules Instruct patients regarding dosing schedules and side effects to report to physician.and side effects to report to physician.



• During therapy, monitor cardiac rhythm, During therapy, monitor cardiac rhythm, heart rate, BP, general well-being, skin color, heart rate, BP, general well-being, skin color, temperature, heart and breath sounds.temperature, heart and breath sounds.

• Assess plasma drug levels as indicated.Assess plasma drug levels as indicated.

• Monitor for toxic effects.Monitor for toxic effects.



• Instruct patients to take medications as Instruct patients to take medications as scheduled and not to skip doses or double scheduled and not to skip doses or double up for missed doses.up for missed doses.

• Patients who miss a dose should contact Patients who miss a dose should contact their physician for instructions if a dose is their physician for instructions if a dose is missed.missed.

• Instruct patients not to crush or chew any Instruct patients not to crush or chew any oral sustained-release preparations.oral sustained-release preparations.



• For class I agents, monitor ECG for QT For class I agents, monitor ECG for QT intervals prolonged more than 50%.intervals prolonged more than 50%.

• IV infusions should be administered with IV infusions should be administered with an IV pump.an IV pump.



• Patients taking propranolol, digoxin, and Patients taking propranolol, digoxin, and other agents should be taught how to take other agents should be taught how to take their own radial pulse for 1 full minute, and to their own radial pulse for 1 full minute, and to notify their physician if the pulse is less than notify their physician if the pulse is less than 60 beats/minute before taking the next dose 60 beats/minute before taking the next dose of medication.of medication.



• Monitor for therapeutic response:Monitor for therapeutic response:

– Decreased BP in hypertensive patientsDecreased BP in hypertensive patients

– Decreased edemaDecreased edema

– Regular pulse rate orRegular pulse rate or

– Pulse rate without major irregularities, orPulse rate without major irregularities, or

– Improved regularity of rhythmImproved regularity of rhythm

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11 Antidysrhythmics Upd