First Reported Experience Using a Lattice-Tip Dual-Energy Catheter Within the Coronary Sinus to Achieve Bidirectional Mitral Annular Block

Background Mitral isthmus (MI) ablation is frequently performed for persistent atrial fibrillation (AF) and mitral annular atrial flutter (AFL), but bidirectional block remains challenging because of tissue thickness, fibrosis, epicardial coronary sinus (CS) connections, and proximity to vascular structures. Objectives To describe the first case series using lattice-tip dual-energy Sphere-9 catheter to deliver temperature-controlled radiofrequency (RF) energy within the CS as an adjunctive epicardial strategy for bidirectional MI block after failed endocardial ablation. Methods Six consecutive patients with drug-refractory AF or AFL underwent endocardial ablation combining pulsed field ablation (PFA) and RF energy. When bidirectional MI block could not be achieved endocardially, CS-based RF ablation was performed using a stepwise temperature-escalation strategy, initiated at 50 °C for 3 seconds and titrated in 5 °C and 2-second increments to a maximum of 60–70 °C for 7 seconds. PFA was avoided within the CS given concern for vasospasm of adjacent coronary structures. Bidirectional block was confirmed by activation sequence reversal and absence of inducible arrhythmias. Results Bidirectional MI block was achieved in all six patients. Three required escalation to 70 °C for 7 seconds for persistent block; in one, initial 60 °C ablation produced only transient block that recovered. No coronary artery injury, pericardial tamponade, or CS perforation was observed. At latest rhythm documentation, all patients remained in normal sinus rhythm. Conclusions Hybrid epicardial MI ablation via the CS using the Sphere-9 catheter with stepwise RF escalation is feasible and appears safe when endocardial ablation is insufficient. Prospective studies are warranted.