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In page Atrial flutter:

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Typical atrial flutter is recognized on an electrocardiogram by the presence of characteristic "flutter waves" at a regular rate of 250 to 350 beats per minute. Flutter waves may not be evident on an ECG in atypical forms of atrial flutter. Individual flutter waves may be symmetrical, resembling p-waves, or maybe asymmetrical with a "sawtooth" shape, rising gradually and falling abruptly or vice versa. If atrial flutter is suspected clinically but is not clearly evident on ECG, acquiring a Lewis lead ECG may be helpful in revealing flutter waves.[citation needed]