Abstract
Spiral waves (SWs) are principal mechanisms of life-threatening ventricular tachyarrhythmias, but their dynamics are not fully understood. We investigated action potential (AP) dynamics of SWs in a 2-dimensional subepicardial layer of rabbit ventricular muscle by using high-resolution optical mapping. The preparations showed uniform anisotropy with an anistropic ratio of conduction at 2.6-3.2. SWs induced by cross-field stimulation rotated around a functional line of block (BL) with periodic meandering. The BL was composed of 2 segments: a central segment (C-BL) with a phase-shift between the two limbs of the circuit, and small terminal segments (T-BLs) with a localized conduction delay around the pivot points. The latter was always parallel to the fiber direction. APs changed gradually from the periphery to the center of the circuit: APs had progressively slower upstroke as close to the pivot points and were transformed into double potentials on the C-BL. INa blockade increased the cycle length (CL) of SWs and prolonged T-BLs. APs on T-BLs showed steps in the depolarization phase, longer duration and shorter electrical diastole as close to the pivot points. ICa,L blockade shortened the C-BL and decreased CL: SWs were more stabilized. These results suggest that depolarization efficiency of SWs depends primarily on the tissue anisotropy and Na channel availability. L-type Ca channel availability may affect the rotation period and stability of SWs through a modulation of AP repolarization. [J Physiol Sci. 2007;57 Suppl:S211]
