  The tunnelling of virtual matter-antimatter pairs from the quantum vacuum in
multidimensions is studied. We consider electric backgrounds as a linear
combination of a spatial Sauter field and, interchangeably, certain weaker time
dependent fields without poles in the complex plane such as the sinusoidal and
Gaussian cases. Based on recent geometric considerations within the worldline
formalism, we employ the relevant critical points in order to analytically
estimate a characteristic threshold for the temporal inhomogeneity. We set
appropriate initial conditions and apply additional symmetry constraints in
order to determine the classical periodic paths in spacetime. Using these
worldline instantons, we compute the corresponding leading order exponential
factors showing large dynamical enhancement in general. We work out the main
differences caused by the analytic structure of such composite backgrounds and
also discuss the case with a strong temporal variation of Sauter-type.
