Arrhythmias may result from abnormalities of impulse initiation (automaticity), conduction (slow conduction, block, reentry), or a combination. The central and peripheral nervous systems have an important influence on the genesis of cardiac arrhythmias. Sympathetic and parasympathetic fibers innervate both atria and ventricle. The study of clinical cardiac arrhythmmias includes the use of invasive and noninvasive testing procedures. The ECG, ambulatory monitoring, esophageal recording, exercise testing, and signal averaging techniques are the currently used noninvasive tests. Intracardiac electrophysiologic studies and endocardial catheter mapping are invasive techniques. The treatment of cardiac arrhythmias includes the use of antiarrhythmic drugs, cardiac pacing (antibradycardia, antitachycardia), implantable automatic defibrillator, cardiac fulguration, and antitachycardiac surgery. Clinical cardiac arrhythmias are of two types, the bradyarrhythmias and the tachyarrhythmias. The tachyarrhythmia, in turn, may be supraventricular or ventricular. There are clinical syndromes specifically related to arrhythmias: preexcitation syndromes are associated with supraventricular tachyarrhythmias, long Q-T syndromes with ventricular tachyarrhythmias, and sick sinus syndrome with bradyarrhythmias. The "tachycardia-bradycardia syndrome" is a combination of atrial tachyarrhythmias and sinus node dysfunction (some of the patients may also have ventricular tachyarrhythmias). Specific arrhythmias are recognized by their ECG characteristics. These arrhythmias also have specific electrophysiologic features which can be defined during invasive electrophysiologic studies. Cardiac arrhythmias may or may not be accompanied by underlying organic heart disease. Their treatment is related to the specific diagnosis and mechanism of the rhythm disturbance. The presence and extent of underlying organic heart disease is an important factor in the selection of antiarrhythmic therapy (drug, pacemaker, or surgery).
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