Nifekalant–Magnesium Cocktail for Chemical Cardioversion of Atrial Flutter: A Multicenter Pilot Study

BACKGROUND: Pharmacologic cardioversion of atrial flutter (AFL) remains challenging, particularly in older or frail patients who are not candidates for catheter ablation. Nifekalant is effective for AFL but is limited by QT prolongation and the risk of torsades de pointes (TdP). Magnesium sulfate may mitigate this risk. METHODS: In this multicenter, investigator-initiated pilot study, 86 patients with symptomatic persistent AFL received intravenous magnesium sulfate followed by nifekalant. The primary outcome was AFL termination within 60 min. Time to termination and safety outcomes, including TdP, were assessed. Multivariable logistic regression analyses were performed to identify factors associated with AFL termination. RESULTS: AFL terminated in 42 patients (48.8%). Among patients with successful cardioversion, 80% achieved termination within 20 min. Larger left atrial diameter was associated with a lower likelihood of AFL termination. Adverse events occurred in 2 patients (2.3%), including sinus pauses requiring pacemaker implantation and transient hypotension requiring vasopressor support. No cases of TdP were observed. CONCLUSIONS: These findings suggest that the nifekalant-magnesium cocktail may be a feasible and potentially safe option for chemical cardioversion of AFL, warranting further investigation in larger studies.