Abstract 2025: Effect of Nifekalant on the Right Atrial Electrophysiologic Characteristics During Typical Atrial Flutter
Background: It has been shown that nifekalant, a novel IKr-selective blocking class III agent, effectively suppresses ventricular tachyarrhythmias. However, its electrophysiologic effects on human atria have not been fully evaluated.
Objectives: The purpose of the study is to elucidate the effects of nifekalant on the electrophysiologic properties of the atrium during typical atrial flutter (AFL).
Methods: Thirteen patients with counter-clockwise typical AFL were studied. A 20-pole “halo” catheter was positioned around the tricuspid annulus, and another 3 catheters were positioned at the His bundle site, coronary sinus and lateral portion of the cavotricuspid annulus (CTI), respectively. Atrial activation was also mapped by the non-contact mapping system (EnSite 3000). During AFL, we measured the conduction time from the lateral to septal CTI (IS) and that through the reminder of the right atrium (nIS). Variability during AFL was quantified by the maximum difference in the cycle length (CL) over 5 consecutive beats. Resetting response curves and atrial effective refractory periods were determined by the single extrastimuli delivered from the lateral CTI. Nifekalant at a dose of 0.2–0.3 mg/kg was administered intravenously.
Results: After infusion of nifekalant, no significant change was observed in the AFL-CL (251.8±32.7 vs. 258.6±36.6 msec, P=NS), IS (71.2±25.8 vs. 73.6±29.6 msec, P=NS) and nIS (180.6±22.0 vs. 185.0±28.4 msec, P=NS). Effective refractory periods and AFL-CL variability increased after administration of nifekalant (161.0±24.7 vs. 178.3±44.8 msec, P<0.05 and 4.0±1.9 vs. 8.3±2.9 msec, P=0.002). The total excitable gap was significantly decreased from 67.7±14.2 to 53.1±13.2 msec (p=0.01) with a rightward shift of the resetting response curves and loss of full excitability. In 9 patients (69%), AFL was terminated spontaneously (n=6) or by single extrastimuli (n=3) which were not effective before administration of nifekalant. Termination was associated with orthodromic block in the CTI.
Conclusions: Nifekalant increases the atrial effective refractory period and AFL-CL variability by abolishment of a full excitable gap, without prolongation of AFL-CL. These unique effects facilitate the termination of AFL.