CHAPTER

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23Antiarrhythmic

Drugs

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Types of Arrhythmias

• Arrhythmias are caused by electrolyte disturbances and overstimulation of the heart and can originate anywhere in the heart.

• Most common types are:– Tachycardias– Premature contractions– Flutters– Fibrillations

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Types of Arrhythmias

• Abnormalities in ECG waves indicate conduction malfunction.

• Several ions help regulate the heart:– Sodium– Potassium– Calcium

• Each one is active during different phases of the cardiac action potential.

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Types of Arrhythmias

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Antiarrhythmic Drugs

• Classified according to the Vaughn-Williams classification system.

• Organized into four major classes based on major mechanism of action.

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The following table shows the Vaughan-Williams classification and the basic mechanism of action associated with each class. Note that Class I drugs are further broken down into subclasses because of subtle, yet important differences in their effects on action potentials.

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Antiarrhythmic Drugs

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Class 1—Sodium Channel Blockers

• Class 1 antiarrhythmic drugs:

– Possess local anesthetic activity

– Block the influx of Na ions during

depolarization

– Suppress arrhythmias in cardiac cells

that are hyperexcitable

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Class 1—Sodium Channel Blockers

• Subdivided into three groups:– IA, IB, IC

• IA:

– Quinidine

– Procainamide

– Disopyramide

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Class 1—Sodium Channel Blockers

• IB:

– Lidocaine

– Mexiletine

• IC:

– Flecanide

– Propafenone

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Class 2—Beta-Blockers

• Decrease heart rate, AV conduction, and automaticity of the SA and AV nodes and heart muscle

• Most common beta-blockers used for arrhythmias:– Propranolol– Acebutolol– Esmolol

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Class 3—Potassium Channel Blockers

• Block potassium during repolarization

• Prolong refractory period and decrease frequency of arrhythmias

• Common Class 3 antiarrhythmics:– Amiodarone– Sotalol– Dofetilide– Ibutilide

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Class 4—Calcium Channel Blockers

• Decrease calcium influx into heart cells

• Slow depolarization

• Decrease heart rate

• Slow conduction of AV node

• Reduce myocardial contractility

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Class 4—Calcium Channel Blockers

• Common calcium channel blockers:– Verapamil

– Diltiazem

– Adenosine

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The drugs that make up the different classes differ in their efficacy (and sometimes safety) for different types of arrhythmias. The following table provides an overview of drug classes and associated arrhythmias. Antiarrhythmic agents that are not included in the Vaughan-Williams scheme are also shown in the table.

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Sinus tachycardia Class II, IVOther underlying causes may need treatment

Atrial fibrillation/flutterClass IA, IC, II, III, IVdigitalis

Ventricular rate control is important goal; anticoagulation is required

Paroxysmal supraventricular tachycardia

Class IA, IC, II, III, IVadenosine

AV block atropine Acute reversal

Ventricular tachycardia Class I, II, III

Premature ventricular complexes

Class II, IVmagnesium sulfate

PVCs are often benign and do not require treatment

Digitalis toxicityClass IBmagnesium sulfate

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Special Considerations

• The control of arrhythmias can be difficult.

• Antiarrhythmic drugs are frequently administered by IV infusion.

• Many anthiarrhythmic drugs are cardiac depressants:– Can produce heart failure

– Can produce new cardiac arrhythmias

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Preferred Therapy

• To stabilize and protect ventricles:– Beta-blockers– Calcium channel blockers– Digoxin

• For chronic therapy of arrhythmias:– Beta-blockers– Calcium channel blockers– Digoxin

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Preferred Therapy

• If there is increased sympathetic tone:– Beta-blockers

• For ventricular tachycardia:– Amiodarone– Lidocaine

• Ventricular arrhythmias & tachycardia:– Amiodarone– Beta-blockers

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