Dynamics of intramural scroll waves in three-dimensional continuous myocardium with rotational anisotropy

It has been suggested that reentrant activity in three-dimensional cardiac muscle may be organized as a scroll wave rotating around a singularity line called the filament. Experimental studies indicate that filaments are ofte n concealed inside the ventricular wall and consequently, scroll waves do n ot, manifest reentrant activity on the surface. Here we analyse how such co ncealed scroll waves are affected by a twisted anisotropy resulting from ro tation of layers of muscle fibers inside the ventricular wall. We used a co mputer model of a ventricular slab (15 x 15 x 15 mm(3)) with a fiber twist of 120 degrees from endocardium to epicardium. The action potential was sim ulated using FitzHugh-Nagumo equations. Scroll waves with rectilinear filam ents were initiated at various depths of the slab and at different angles w ith respect to fiber orientation. The analysis shows that independent of in itial conditions, after a certain transitional period, the filament aligns with the local fiber orientation. The alignment of the filament is determin ed by the directional variations in cell coupling due to fiber rotation and by boundary conditions. Our findings provide a mechanistic explanation for the prevalence of intramural reentry over transmural reentry during polymo rphic ventricular tachycardia and fibrillation. (C) 1999 Academic Press.