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In page Atrial flutter:

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Atrial flutter is caused by a re-entrant rhythm. This usually occurs along the cavo-tricuspid isthmus of the right atrium though atrial flutter can originate in the left atrium as well. Typically initiated by a premature electrical impulse arising in the atria, atrial flutter is propagated due to differences in refractory periods of atrial 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 atria.[citation needed]