Parallel Septal Balloon Occlusion for Acute Right-to-Left Shunt During Mitral Transcatheter Edge-to-Edge Repair.

BACKGROUND: Mitral transcatheter edge-to-edge repair (M-TEER) requires large-bore transseptal puncture, creating an iatrogenic atrial septal defect (IASD). Right-to-left shunting across an IASD is rare but can cause significant hypoxemia in high-risk patients. CASE SUMMARY: A 78-year-old man with nonischemic cardiomyopathy and severe mitral and tricuspid regurgitation underwent M-TEER. Profound hypoxemia secondary to acute right-to-left shunt developed immediately after transseptal instrumentation with a large-bore sheath. A compliant sizing balloon was inflated across the septal defect in parallel with the transseptal sheath, restoring oxygenation and allowing safe deployment of the PASCAL (Edwards Lifesciences) valve, with septal closure performed at the end of the procedure. DISCUSSION: This case illustrates a distinctive predeployment presentation of right-to-left IASD shunting and a novel bailout technique that preserves transseptal access without requiring additional venous puncture. TAKE-HOME MESSAGES: Right-to-left IASD shunting should be anticipated in patients with high-risk hemodynamic profiles before transseptal puncture. Parallel balloon septal occlusion represents a practical bridging strategy enabling safe M-TEER completion.