  Rotating scroll waves are self-organising patterns which are found in many
oscillating or excitable systems. Here we show that quasi-periodic (meandering)
scroll waves, which include the rotors that organise cardiac arrhythmias,
exhibit filament tension when averaged over the meander cycle. With strong
filament curvature or medium thickness gradients, however, scroll wave dynamics
are governed by phase-locked drift instead of filament tension. Our results are
validated in computational models of cycloidal meander and a cardiac tissue
model with linear core.
