Atypical Atrial Flutter From Lipomatous Hypertrophy of the Interatrial Septum in a Procedure-Naive Patient

BACKGROUND: Lipomatous hypertrophy of the interatrial septum (LHIS) is generally benign and often discovered incidentally; however, it can occasionally serve as a substrate for atrial arrhythmias. CASE SUMMARY: An 86-year-old man with no prior cardiac history presented with new onset atrial flutter (AFL) with an atrial rate of 280 beats/min. During an electrophysiology study, intracardiac echocardiography identified LHIS. Three-dimensional electroanatomic activation mapping demonstrated the earliest focal activation at the superior posteroseptal right atrium, corresponding to the location of the LHIS. Radiofrequency ablation at this site terminated the AFL, rendering the tachycardia noninducible. DISCUSSION: LHIS can act as an isolated arrhythmogenic substrate for atypical AFL. The combination of intracardiac echocardiography and high-density electroanatomic mapping allows precise localization of the arrhythmogenic focus, facilitating safe and effective catheter ablation. TAKE-HOME MESSAGES: LHIS should be considered a potential arrhythmogenic substrate in patients with atypical AFL. Catheter ablation of LHIS-associated AFL is safe and effective.