English Reading Materials Chapter 19:Agents Used in Cardiac Arrhythmias INTRODUCTION Cardiac arrhythmias are a frequent problem in clinical practice,occurring in up to 25%of patients treated with digitalis,50%of anesthetized patients,and over 80%of patients with acute myocardial infarction.Arrhythmias may require treatment because rhythms that are too rapid,too slow,or asynchronous can reduce cardiac output.Some arrhythmias can precipitate more serious or even lethal rhythm disturbances eg, early premature ventricular depolarizations can precipitate ventricular fibrillation.In such patients,antiarrhythmic drugs may be lifesaving.On the other hand,the hazards of antiarrhythmic drugs and in particular the fact that they can precipitate lethal arrhythmias in some patients has led to a reevaluation of their relative risks and benefits.In general,treatment of asymptomatic or minimally symptomatic arrhythmias should be avoided for this reason. Arrhythmias can be treated with the drugs discussed in this chapter and with nonpharmacologic therapies such as pacemakers,cardioversion,catheter ablation,and surgery.This chapter describes the pharmacology of drugs that suppress arrhythmias by a direct action on the cardiac cell membrane.Other modes of therapy are discussed briefly(see Box,The Nonpharmacologic Therapy of Cardiac Arrhythmias) THE NONPHARMACOLOGIC THERAPY OF CARDIAC ARRHYTHMIAS It was recognized over 100 years ago that reentry in simple in vitro models (eg,rings of conducting tissues)was permanently interrupted by transecting the reentry circuit. This concept is now applied in cardiac arrhythmias with defined anatomic pathways eg,atrioventricular reentry using accessory pathways,atrioventricular node reentry,atrial flutter,and some forms of ventricular tachycardia by treatment with radiofrequency catheter ablation.Recent studies have shown that paroxysmal and persistent atrial fibrillation may arise from one of the pulmonary veins.Both forms of atrial fibrillation can be cured by electrically isolating the pulmonary veins by radiofrequency catheter ablation or during concomitant cardiac surgery. Another form of nonpharmacologic therapy is the implantable cardioverter-defibrillator (ICD),a device that can automatically detect and treat potentially fatal arrhythmias such as ventricular fibrillation.ICDs are now widely used in patients who have been resuscitated from such arrhythmias,and several trials have shown that ICD treatment reduces mortality in patients with coronary artery 11 English Reading Materials Chapter 19: Agents Used in Cardiac Arrhythmias INTRODUCTION Cardiac arrhythmias are a frequent problem in clinical practice, occurring in up to 25% of patients treated with digitalis, 50% of anesthetized patients, and over 80% of patients with acute myocardial infarction. Arrhythmias may require treatment because rhythms that are too rapid, too slow, or asynchronous can reduce cardiac output. Some arrhythmias can precipitate more serious or even lethal rhythm disturbances eg, early premature ventricular depolarizations can precipitate ventricular fibrillation. In such patients, antiarrhythmic drugs may be lifesaving. On the other hand, the hazards of antiarrhythmic drugs and in particular the fact that they can precipitate lethal arrhythmias in some patients has led to a reevaluation of their relative risks and benefits. In general, treatment of asymptomatic or minimally symptomatic arrhythmias should be avoided for this reason. Arrhythmias can be treated with the drugs discussed in this chapter and with nonpharmacologic therapies such as pacemakers, cardioversion, catheter ablation, and surgery. This chapter describes the pharmacology of drugs that suppress arrhythmias by a direct action on the cardiac cell membrane. Other modes of therapy are discussed briefly (see Box, The Nonpharmacologic Therapy of Cardiac Arrhythmias). THE NONPHARMACOLOGIC THERAPY OF CARDIAC ARRHYTHMIAS It was recognized over 100 years ago that reentry in simple in vitro models (eg, rings of conducting tissues) was permanently interrupted by transecting the reentry circuit. This concept is now applied in cardiac arrhythmias with defined anatomic pathways eg, atrioventricular reentry using accessory pathways, atrioventricular node reentry, atrial flutter, and some forms of ventricular tachycardia by treatment with radiofrequency catheter ablation. Recent studies have shown that paroxysmal and persistent atrial fibrillation may arise from one of the pulmonary veins. Both forms of atrial fibrillation can be cured by electrically isolating the pulmonary veins by radiofrequency catheter ablation or during concomitant cardiac surgery. Another form of nonpharmacologic therapy is the implantable cardioverter-defibrillator (ICD), a device that can automatically detect and treat potentially fatal arrhythmias such as ventricular fibrillation. ICDs are now widely used in patients who have been resuscitated from such arrhythmias, and several trials have shown that ICD treatment reduces mortality in patients with coronary artery