Electrical-anatomic correlations between typical atrial flutter and intra-atrial re-entry following atrial surgery

It is well known that in typical (or type I) atrial flutter, conduction proceeds counterclockwise, up the interatrial septum and down the right atrial wall anterior to the crista terminalis (CT). Recent careful mapping studies using entrainment pacing have clearly shown the importance of the CT and the eustachian valve ridge (EVR), which act as fixed barriers to intraatrial conduction and interact with other barriers, including the tricuspid valve, inferior vena cava (IVC), and coronary 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 cardiac surgery may have typical atrial flutter, either counterclockwise or clockwise, and prior surgery may act to stabilize the circuit. Such patients may also have atypical flutter, which does not utilize this circuit. Surgical closure of septal defects requires a long anterior oblique atriotomy. Commonly, reentrant circuits are identified that use this barrier, as well as the tricuspid valve and CT, and are confined to the anterior atrial wall and do not involve the typical flutter isthmus. These may be ablated at the lower or the upper end of the atriotomy, extending the block to the tricuspid valve, IVC, or superior vena cava. After the Senning or Mustard procedure, typical flutter is common, and the baffle bisects the isthmus at the site of the EVR, perhaps enforcing 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' Fontan (cavopulmonary connection) suture lines are similar to those of the Senning procedure, but nearly all right atrial anatomy is in the pulmonary venous atrium. Such circuits may need to be approached via an atrial fenestration.