  Helicity amplitudes and differential cross section of high-energy $e^+e^-$
photoproduction accompanied by bremsstrahlung in the electric field of a heavy
atom are derived. The results are exact in the nuclear charge number and
obtained in the leading quasiclassical approximation. They correspond to the
leading high-energy small-angle asymptotics of the amplitude. It is shown that,
in general, the Coulomb corrections essentially modify the differential cross
section as compared to the Born result. When the initial photon is circularly
polarized the Coulomb corrections lead to the asymmetry in the distribution
over the azimuth angles $\varphi_i$ of produced particles with respect to the
replacement $\varphi_i\to -\varphi_i$.
