1. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 1 CHAPTER 23 Antiarrhythmic Drugs

2. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 2 Cardiac Arrhythmias Arrhythmias are disturbances in the normal electrical activity of the heart Arrhythmias can be detected on a recording of the electrocardiogram (ECG) Supraventricular arrhythmias occur above the ventricles in the atria, SA node, and AV node Ventricular arrhythmias occur in the ventricles and Purkinje fibers and are usually more serious and life-threatening

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5. 5 Electrophysiological Properties of the Heart Excitability – associated with membrane depolarization and the influx of Na ions Refractory period – associated with repolarization and the efflux of K ions Automaticity – ability of the SA and AV nodes to initiate membrane depolarizations Under conditions of hypoxia and excessive sympathetic stimulation, the ventricles can also demonstrate automaticity to cause ectopic beats or PVCs

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8. 8 Quinidine and Procainamide Classified as class 1 antiarrhythmic drugs Possess local anesthetic activity and block the influx of Na ions during depolarization Main effects are to decrease excitability, slow conduction, and prolong the refractory period ECG: prolong the PR, QRS, and QT intervals Used for both supraventricular and ventricular arrhythmias

9. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 9 Lidocaine Class 1 local anesthetic-type antiarrhythmic used only for ventricular arrhythmias Must be administered IV by infusion The drug of choice in acute and emergency ventricular arrhythmias Main effect is to decrease automaticity Mexiletine and tocainide are similar to lidocaine and can be administered orally

10. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 10 Propranolol Classified as a class 2 antiarrhythmic drug Primarily blocks cardiac beta receptors to slow heart rate, AV conduction, and prolong the refractory period ECG: mainly increases the PR interval Used for both supraventricular and ventricular arrhythmias

11. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 11 Amiodarone Classified as a class 3 antiarrhythmic drug Usually reserved for more serious arrhythmias when other drugs have failed Main effect is to prolong the refractory period and increase the QT interval Drug contains iodine and can interfere with thyroid function

12. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 12 Verapamil and Diltiazem Classified as class 4 antiarrhythmic drugs Act by blocking calcium ions Main effects are to decrease heart rate and AV conduction, increase the PR interval Mainly used to treat supraventricular arrhythmias May cause cardiac depression at higher doses

13. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 13 Adenosine Administered IV in emergency situations Main action is to decrease AV conduction and slow the heart rate Used to treat acute supraventricular tachycardia Duration of action is 15–30 seconds