[en] The effect of quadrupole-octupole deformations on the energy and magnetic properties of high-K isomeric states in even-even heavy and superheavy nuclei is studied within a deformed shell model (DSM) with BCS pairing interaction. The neutron two-quasiparticle (2qp) isomeric energies and magnetic dipole moments are calculated over a wide range of quadrupole and octupole deformations. It is found that in most of the considered nuclei the magnetic moments exhibit a pronounced sensitivity to the octupole deformation. At the same time in many cases the behaviour of the 2qp energies shows minima which suggest that the presence of high-K isomeric states may be associated with the presence of octupole softness or even with octupole deformation. In the present work the influence of the BCS pairing strength on the energy of the blocked isomer configuration is examined. The analysis of the 2qp energy minima obtained in the space of quadrupole-octupole deformations for different pairing strengths shows that the formation of high-K isomeric states is a subtle effect depending on both, deformations and nuclear pairing correlations. (author)