ATRIAL-FLUTTER MAPPING AND ABLATION .1. STUDYING ATRIAL-FLUTTER MECHANISMS BY MAPPING AND ENTRAINMENT

Endocardial mapping has led to a detailed knowledge of reentry mechani sms in atrial flutter. Multipolar and deflecting tip catheters allow r ecording local electrograms from multiple areas of the right atrium, a nd from the coronary sinus. In common flutter, with the typical ''sawt ooth'' pattern, there is a circular activation of the right atrium in a ''counterclockwise'' direction, descending in the anterior and later al walls, and ascending in the septum and posterior wall. Superior and inferior vena cava, linked by a ''line'' of functional block in the p osterolateral wall, make the central obstacle for circular activation. The cranial and caudal turning points are the atrial ''roof'', and th e isthmus between the inferior vena cava and the tricuspid valve. Comp lex conduction patterns, probably including slow conduction are detect able in the low septal area, around the coronary sinus. Atypical flutt er, without the sharp negative deflections of common flutter, sometime s shows circular activation in the right atrium, rotating in the oppos ite direction of common flutter (clockwise). Other atypical flutters s how no circular right atrial activation, and only partial data from co ronary sinus activation, combined with the response to atrial stimulat ion (entrainment) allow the diagnosis of left atrial reentry, without a precise delimitation of the circuits. In patients having undergone c ardiac surgery, atypical flutter may be based on reentry around surgic al scars. To our knowledge, the mechanism of type II flutter has not b een disclosed in humans.