Atypical right atrial flutter patterns

Background-The purpose of our study was to define the incidence and mechani sms of atypical right atrial flutter, Methods and Results-A total of 28 (8%) of 372 consecutive patients with atr ial flutter (AFL) had 36 episodes of sustained atypical right AFL, Among 24 (67%) of 36 episodes of lower loop reentry (LLR), 13 (54%) of 24 episodes had early breakthrough at the lower lateral tricuspid annulus, whereas 11 ( 46%) of 24 episodes had early breakthrough at the high lateral tricuspid an nulus, and 9 (38%) of 24 episodes showed multiple annular breaks. Bidirecti onal isthmus block resulted in elimination of LLR, A pattern of posterior b reakthrough from the eustachian ridge to the septum was observed in 4 (14%) of 28 patients. Upper loop reentry was observed in 8 (22%) of 36 episodes and was defined as showing a clockwise orientation with early annular break and wave front collision over the isthmus, Two patients had atypical right AFL around low voltage areas ("scars") in the posterolateral right atrium. Conclusions-Atypical right AFL is most commonly associated with an isthmus- dependent mechanism (ie, LLR or subeustachian isthmus breaks). Non-isthmus- dependent circuits include upper loop reentry or scar-related circuits.