Disturbances in the sophisticated electrical wiring of the heart lead to abnormalities of the heart rhythm, or arrhythmia. The study and treatment of these arrhythmias is called electrophysiology. Arrhythmias can be divided into bradycardia (slow heart beat) and tachycardia (fast heart beat).

Bradycardias usually result from degenerative disease of the conduction nerves and nerve centers in the heart, such as the sinus node, AV node, and bundle of His. For example, the sinus node may fire too slowly or not fire at all, causing sinus arrest. In this setting, one of the backup pacemaker centers of the heart takes over, usually at a very slow heart rate. Alternatively, the AV node may conduct too slowly or not at all, causing a breakdown in communication between the atria and ventricles, or AV dissociation. Severe disease in the Bundle of His may also cause AV dissociation. Some bradycardias may also result from high dose of medications, such as beta blockers. Bradycardias may cause symptoms such as weakness, dizziness, or fainting spells. Severe bradycardias are treated with a pacemaker.

Tachycardias are characterized by an erratic, rapid beating of the heart that overrides the normal SA node pacemaker. Tachycardias that have their origin in the atria are called atrial tachycardias. These include atrial fibrillation, atrial flutter, and atrial tachycardia.

Atrial fibrillation is a very common arrhythmia characterized by a very rapid and irregular beating of the heart. This arrhythmia is usually treated with digoxin or a beta blocker for control of the heart rate. Other antyrrhythmic drugs, such as sotalol, disopyramide, or amiodarone may be added to suppress the fibrillation rhythm itself. In some cases, electrical shock can be used to convert the patient back to sinus rhythm. Since atrial fibrillation may lead to the formation of blood clots in the heart, patients with atrial fibrillation are usually treated with coumadin, a potent blood thinner, to prevent the occurance of stroke.

Atrial flutter and atrial tachycardia typically cause symptoms of palpitations or lightheadedness.

Tachycardias that originate in the ventricles, termed ventricular tachycardias, are usually more dangerous in that they may cause severe drops in blood pressure, leading to loss of consciousness. Some of these arrhythmias can be controlled with medications. However, some severe tachycardias cause repeated lapses of consciousness and are life-threatening. These are treated with an automatic implantable cardiac defibrillator (AICD), a device implanted under the skin that detects a dangerous tachycardia and terminates it with an electrical shock. Some difficult-to-treat tachycardias that do not respond to medicine may be ablated by radiofrequency catheter ablation therapy, which is done through a catheter in the groin.

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