<unk>  is caused by a re-entrant rhythm. This usually occurs along the cavo-tricuspid isthmus of the right atrium though<unk>  can originate in the left atrium as well. Typically initiated by a premature electrical impulse arising in the<unk> <unk>  is propagated due to differences in refractory periods of<unk>  tissue. This creates electrical activity that moves in a localized self-perpetuating loop, which usually lasts about 200 milliseconds for the complete circuit. For each cycle around the loop, an electric impulse results and propagates through the<unk>  The impact and symptoms of<unk>  depend on the heart rate of the<unk> fected person. Heart rate is a measure of ventricular rather than<unk>  activity. Impulses from the<unk> are conducted to the ventricles through the atrio-ventricular node (AV node). In a person with<unk> , a 12-lead electrocardiogram (ECG) will demonstrate the<unk>  chambers of the heart contracting at a rate of 280–300 beats per minute whereas the ventricular chambers of the heart typically beat at a rate of 140–150 beats per minute. Due primarily to its longer refractory period, the AV node exerts a protective effect on heart rate by blocking<unk>  impulses in excess of about 180 beats/minute, for the example of a resting heart rate. (This block is dependent on the age of the patient, and can be calculated roughly by subtracting patient age from 220). If the<unk>  rate is 300/minute only half of these impulses will be conducted, giving a ventricular rate of 150/minute, or a 2:1 heart block. The addition of rate-controlling drugs or conduction system disease can increase this block substantially
Atrial flutter
Ventricular flutter
Sinus arrhythmia
Supraventricular tachycardia
Atrial fibrillation
Ventricular fibrillation
Left bundle branch block
Junctional tachycardia