Modification by pion exchange of near threshold resonance line shape in open heavy flavor channel

The effect of the pion exchange on the line shape of near threshold bottomoniumlike resonances decaying into an $S$ wave pair of $B^{(\ast )}$ mesons is considered. It is pointed out that this effect, parametrically enhanced by the heavy meson mass, can be of a practical significance in determining the parameters of the bottomoniumlike resonances such as the known $Z_b(10610)$ and $Z_b(10650)$ states.