Importance of atrial flutter isthmus in postoperative intra-atrial reentrant tachycardia

Background-In survivors of congenital heart surgery, intra-atrial reentrant tachycardia (IART) often develops. Previous reports have emphasized the at riotomy scar as the central barrier around which a reentrant circuit may ro tate but have not systematically evaluated the atrial flutter isthmus in su ch patients. We sought to determine the role of the atrial flutter isthmus in supporting IART in a group of postoperative patients with congenital hea rt disease. Methods and Results-Nineteen postoperative patients with IART underwent ele ctrophysiological studies with entrainment mapping of the atrial flutter is thmus for determining postpacing intervals. Radiofrequency ablation was per formed at the identified isthmus in an effort to create a complete line of block. Twenty-one IARTs were identified in 19 patients, with a mean tachyca rdia cycle length of 293 +/- 73 ms. The atrial flutter isthmus was part of the circuit in 15 of 21 (71.4%). In the remaining 6 of 21, the ablation tar get zone was at sites near atrial incisions or suture lines. Ablation was s uccessful in 19 of 21 (90.4%) IARTs and in 14 of 15 (93.3%) cases at the at rial flutter isthmus. Conclusions-In most of our postoperative patients, the atrial flutter isthm us was part of the reentrant circuit. The fact that the atrial flutter isth mus is vulnerable to ablation suggests that whenever IART occurs late after repair of a congenital heart defect, the atrial flutter isthmus should be evaluated. These data support the theory that some form of conduction block between the vena cava is essential for the establishment of a stable subst rate for the atrial flutter reentrant circuit.