Atypical atrial flutters.

Typical atrial flutter is due to a counterclockwise macro-re-entry circuit localized in the right atrium with a surface ECG pattern showing predominantly negative F waves in the inferior leads and positive F waves in V1. Recently it has been proposed to classify atrial flutter on the basis of its cavo-tricuspid isthmus dependence rather than on the ECG pattern. Therefore some atrial flutters are considered typical even if the ECG does not exhibit a typical pattern. This is the case for reverse typical atrial flutter, lower loop re-entry and partial-isthmus-dependent short circuit flutter. The term atypical flutter refers to a non-isthmus dependent flutter. Usually these patients have had previous cardiac surgery with a right or left atriotomy. Flutter involving a spontaneous right atrial scar is not uncommon.