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Types of Arrhythmias

Arrhythmias are categorized by their speed.

Bradycardia = slow heart rate
Tachycardia = fast heart rate
Fibrillation = fast, uncoordinated beats — a quivering heart

Some common arrhythmias include:

Supraventricular tachycardia is a burst of rapid heartbeats that originates in your heart's upper chambers. The bursts usually begin and end suddenly. Episodes can last seconds to days.

Atrial flutter is when the heart's upper chambers flutter, beating rapidly. Atrial flutter is often associated with damage to the heart caused by a faulty heart valve.
Atrial fibrillation is a very common arrhythmia, affecting mainly older people. In atrial fibrillation, the heart's upper chambers beat very fast (300 to 600 beats a minute) and chaotically. The ventricles also speed up, resulting in an irregular and often rapid heart rhythm.

Wolff-Parkinson-White syndrome, named after the physicians who first described it, is caused by an extra electrical pathway that develops between the heart's upper and lower chambers. This extra pathway allows too many electrical impulses to reach the ventricles, speeding up the heart rate.

Ventricular tachycardia is when faulty electrical signals that arise from your heart's lower chambers cause your ventricles to beat too fast. Ventricular tachycardia is almost always associated with heart disease or recent heart attack and can deteriorate to the most serious form of fast heartbeat — ventricular fibrillation.

Ventricular fibrillation is considered a medical emergency. Chaotic electrical signals through your heart's lower chambers cause your heart to suddenly quiver uselessly and cease pumping. Most people lose consciousness seconds later and require some type of immediate emergency medical assistance, such as CPR. Unless the heart is shocked back into a normal rhythm by a device called a defibrillator, ventricular fibrillation results in sudden death.

Long QT syndrome is an inherited arrhythmia, involving a defect in the ventricles. QT refers to a pattern seen on an electrocardiogram — a test that measures the electrical impulses of the heart. These impulses, read from electrodes attached to the chest, are recorded as waves. The different peaks and valleys of these waves are designated by letters — P, Q, R, S and T. The Q-to-T interval represents the firing and resting of the ventricles during each heartbeat. Doctors measure this interval and can tell if a QT interval takes a normal amount of time or takes too long and results in rapid heartbeats.

Sick sinus syndrome is when the heart's sinus node isn't firing right, your heart rate slows down or slows down and then speeds up. Sick sinus syndrome, which is common in older people, is considered a type of bradycardia. This arrhythmia sometimes accompanies atrial fibrillation.

Heart block occurs when the electrical pathways that run between your heart's upper and lower chambers and through your heart's lower chambers become blocked, slowing the transmission of electrical impulses through the heart. The result is a very slow heart rate (bradycardia).

Premature beats are the most common arrhythmia, premature beats—which affect a large number of people, especially older Americans—are benign and are often described as "flip-flops." Caffeine and stress increase the occurrence of premature beats.