ELECTRICAL-ANATOMIC CORRELATIONS BETWEEN TYPICAL ATRIAL-FLUTTER AND INTRAATRIAL REENTRY FOLLOWING ATRIAL SURGERY

It is well known that in typical (or type I) atrial flutter, conductio n proceeds counterclockwise, up the interatrial septum and down the ri ght atrial wall anterior to the crista terminalis (CT). Recent careful mapping studies using entrainment pacing have clearly shown the impor tance of the CT and the eustachian valve ridge (EVR), which act as fix ed barriers to intraatrial conduction and interact with other barriers , including the tricuspid valve, inferior vena cava (IVC), and coronar y sinus os, to create a long macroreentrant circuit. Ablative lesions are directed at the isthmus between the tricuspid valve and the IVC or between the tricuspid valve and the EVR. Patients who have had cardia c surgery may have typical atrial flutter, either counterclockwise or clockwise, and prior surgery may act to stabilize the circuit. Such pa tients may also have atypical flutter, which does not utilize this cir cuit. Surgical closure of septal defects requires a long anterior obli que atriotomy. Commonly, reentrant circuits are identified that use th is barrier, as well as the tricuspid valve and CT, and are confined to the anterior atrial wall and do not involve the typical flutter isthm us. These may be ablated al the lower or the upper end of the atriotom y, extending the block to the tricuspid valve, IVC, or superior vena c ava. After the Senning or Mustard procedure, typical flutter is common , and the baffle bisects the isthmus at the site of the EVR, perhaps e nforcing block. Anterior atriotomy-mediated reentry also is seen, and both circuits need to be approached in a retrograde manner. After the Fontan atriopulmonary connection, atriotomies and atrial dilation may interact to make reentry more likely. After the ''lateral tunnel'' Fon tan (cavopulmonary connection) suture lines are similar to those of th e Senning procedure, but nearly all right atrial anatomy is in the pul monary venous atrium. Such circuits may need to be approached via an a trial fenestration.