CHAPTER 23 Antiarrhythmic Drugs 2012 The Mc GrawHill

23 -2 Types of Arrhythmias • Arrhythmias are caused by electrolyte disturbances and overstimulation

23 -3 Types of Arrhythmias • Abnormalities in ECG waves indicate conduction malfunction. •

23 -4 Types of Arrhythmias © 2012 The Mc. Graw-Hill Companies, Inc. All rights

23 -5 Antiarrhythmic Drugs • Classified according to the Vaughn. Williams classification system. •

1 -6 The following table shows the Vaughan. Williams classification and the basic mechanism

23 -7 Antiarrhythmic Drugs © 2012 The Mc. Graw-Hill Companies, Inc. All rights reserved.

23 -8 Class 1—Sodium Channel Blockers • Class 1 antiarrhythmic drugs: – Possess local

23 -9 Class 1—Sodium Channel Blockers • Subdivided into three groups: – IA, IB,

23 -10 Class 1—Sodium Channel Blockers • IB: – Lidocaine – Mexiletine • IC:

23 -11 Class 2—Beta-Blockers • Decrease heart rate, AV conduction, and automaticity of the

$23 -12 Class 3—Potassium Channel Blockers • Block potassium during repolarization • Prolong refractory$

23 -13 Class 4—Calcium Channel Blockers • Decrease calcium influx into heart cells •

23 -14 Class 4—Calcium Channel Blockers • Common calcium channel blockers: – Verapamil –

1 -15 The drugs that make up the different classes differ in their efficacy

1 -16 Sinus tachycardia Class II, IV Other underlying causes may need treatment Atrial

23 -17 Special Considerations • The control of arrhythmias can be difficult. • Antiarrhythmic

23 -18 Preferred Therapy • To stabilize and protect ventricles: – Beta-blockers – Calcium

23 -19 Preferred Therapy • If there is increased sympathetic tone: – Beta-blockers •

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23 -2 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 © 2012 The Mc. Graw-Hill Companies, Inc. All rights reserved.

23 -3 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. © 2012 The Mc. Graw-Hill Companies, Inc. All rights reserved.

23 -5 Antiarrhythmic Drugs • Classified according to the Vaughn. Williams classification system. • Organized into four major classes based on major mechanism of action. © 2012 The Mc. Graw-Hill Companies, Inc. All rights reserved.

1 -6 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. © 2012 The Mc. Graw-Hill Companies, Inc. All rights reserved.

23 -8 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 © 2012 The Mc. Graw-Hill Companies, Inc. All rights reserved.

23 -11 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 © 2012 The Mc. Graw-Hill Companies, Inc. All rights reserved.

$23 -12 Class 3—Potassium Channel Blockers • Block potassium during repolarization • Prolong refractory$

23 -12 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 © 2012 The Mc. Graw-Hill Companies, Inc. All rights reserved.

23 -13 Class 4—Calcium Channel Blockers • Decrease calcium influx into heart cells • Slow depolarization • Decrease heart rate • Slow conduction of AV node • Reduce myocardial contractility © 2012 The Mc. Graw-Hill Companies, Inc. All rights reserved.

1 -15 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. © 2012 The Mc. Graw-Hill Companies, Inc. All rights reserved.

1 -16 Sinus tachycardia Class II, IV Other underlying causes may need treatment Atrial fibrillation/flutter Class IA, IC, III, IV digitalis Ventricular rate control is important goal; anticoagulation is required Paroxysmal Class IA, IC, III, IV supraventricular tachycardia adenosine AV block atropine Ventricular tachycardia Class I, III Premature ventricular complexes Class II, IV magnesium sulfate Digitalis toxicity Class IB magnesium sulfate Acute reversal PVCs are often benign and do not require treatment © 2012 The Mc. Graw-Hill Companies, Inc. All rights reserved.

23 -17 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 © 2012 The Mc. Graw-Hill Companies, Inc. All rights reserved.

23 -18 Preferred Therapy • To stabilize and protect ventricles: – Beta-blockers – Calcium channel blockers – Digoxin • For chronic therapy of arrhythmias: – Beta-blockers – Calcium channel blockers – Digoxin © 2012 The Mc. Graw-Hill Companies, Inc. All rights reserved.

23 -19 Preferred Therapy • If there is increased sympathetic tone: – Beta-blockers • For ventricular tachycardia: – Amiodarone – Lidocaine • Ventricular arrhythmias & tachycardia: – Amiodarone – Beta-blockers © 2012 The Mc. Graw-Hill Companies, Inc. All rights reserved.