Abstract Body (Do not enter title and authors here): Background
Catheter ablation of typical atrial flutter (AFL) typically relies on femoral venous access. Inferior vena cava (IVC) interruption is a congenital anomaly that complicates right heart access. Alternative approaches, including jugular or axillary access have been described, but catheter stability and limited intraprocedural imaging are challenges. We present a novel case of AFL ablation using superior venous access for mapping and ablation paired with femoral access for intracardiac echocardiography (ICE) from the azygous vein.

Description of Case
A 66-year-old woman with paroxysmal AFL and dual-chamber pacemaker presented with symptomatic AFL and variable AV block. A prior ablation attempt was aborted after bilateral femoral access attempts revealed interrupted IVC with anomalous SVC return via a dilated azygous vein. CT scan confirmed IVC interruption and azygous continuation coursing posterior to the left atrium. A second ablation attempt succeeded using superior access via the right internal jugular (RIJ) and left axillary vein (LAV) to advance ablation and coronary sinus catheters. An ICE catheter was introduced via femoral vein and navigated to the thoracic azygous vein imaging directly behind the heart. This gave excellent imaging of the right atrium and cavotricuspid isthmus (CTI). Ablation with a contact-force irrigated catheter via the LAV improved catheter stability compared to the RIJ approach.

Discussion
This is the first report using ICE from the azygous vein via the femoral route for intraprocedural imaging of CTI ablation. The posterior trajectory of the azygous vein enabled ICE imaging in planes similar to transesophageal echocardiography. Superior access from RIJ and LAV allowed mapping and ablation despite the absence of IVC continuity. Ablation on the CTI with a superior approach is challenging. Reduced catheter contact and stability can result in breakthrough of the lesion set and recurrence of AFL. ICE provides visual feedback to ensure catheter contact and stability. This approach overcomes several limitations in patients with interrupted IVC.

Conclusion
In patients with IVC interruption, superior venous access for catheter manipulation combined with transfemoral ICE catheter placement in the azygous vein is a novel, effective strategy for AFL ablation. This technique enables high-resolution imaging and improved catheter stability, expanding options for successful AFL ablation in patients with complex venous anatomy.