  Spiral waves of excitation in cardiac tissue are associated with
life-threatening cardiac arrhythmias. It is, therefore, important to study the
electrophysiological factors that affect the dynamics of these spiral waves. By
using an electrophysiologically detailed mathematical model of a myocyte
(cardiac cell), we study the effects of cellular parameters, such as
membrane-ion-channel conductances, on the properties of the action-potential
(AP) of a myocyte. We then investigate how changes in these properties,
specifically the upstroke velocity and the AP duration (APD), affect the
frequency $\omega$ of a spiral wave in the mathematical model that we use for
human-ventricular tissue. We find that an increase (decrease) in this
upstroke-velocity or a decrease (increase) in the AP duration increases
(decreases) $\omega$. We also study how other intercellular factors, such as
the fibroblast-myocyte coupling, diffusive coupling strength, and the effective
number of neighboring myocytes, modulate $\omega$. Finally, we demonstrate how
a spiral wave can drift to a region with a high density of fibroblasts. Our
results provide a natural explanation for the anchoring of spiral waves in
highly fibrotic regions in fibrotic hearts.
