Flecainide widens the excitable gap at pivot points of premature turning wavefronts in rabbit ventricular myocardium

Introduction: The mechanisms by which Class IC drugs slow the rate of funct ional reentrant arrhythmias are not completely understood. We hypothesized that flecainide widens the excitable gap beyond the pivot point of prematur e turning wavefronts. Methods and Results: In eight perfused subepicardial layers of rabbit left ventricle, a linear lesion was made by radiofrequency (RF) ablation paralle l to the fiber orientation. One end of the RF lesion was extended by a shor t incision. Pacing next to the lesion induced a wavefront propagating with a sharp U-turn around the end of the lesion in either the clockwise or coun terclockwise direction. A high-density mapping electrode (240 electrodes, 3 50-mum resolution) was used to record unipolar electrograms at the pivot po int. During control, the shortest V1-V2 interval proximal to the pivot poin t was 162 +/- 12 msec compared with 173 +/- 13 msec distal to the pivot poi nt (difference 11 +/-8 msec; P<0.01). After infusion of flecainide 2 mg/L, the shortest V1-V2 interval proximal and distal to the pivot point were 217 <plus/minus>29 msec and 244 +/- 36 msec (difference 27 +/- 16 msec; P<0.01) . Due to the increase in V1-V2 interval at the pivot point, flecainide wide ned the temporal excitable gap in the returning limb of the turning wavefro nt from 30<plus/minus>11 msec to 55 +/- 22 msec (P<0.01). High-density mapp ing at the pivot point revealed that this widening of the excitable gap was due to both macroscopic discontinuous conduction and functional conduction block at the pivot point. Conclusion: Flecainide widens the excitable gap in the returning limb of pr emature U-turning wavefronts by causing macroscopic discontinuous conductio n and functional conduction block at the pivot point.