Nitrogen doped 4H-SiC epitaxial layers grown by hot-wall chemical vapor deposition were investigated by Deep Level Transient Spectroscopy after irradiation with 6 MeV electrons at room temperature. This study is focusing on the influence of nitrogen doping and C/Si ratio on the behaviour of the Z1,2 and EH6,7 levels which occur in already as-grown material but are substantially enhanced by electron and ion irradiation. It was found that both the Z1,2 and EH6,7 concentrations increase with both the nitrogen doping and the C/Si ratio. However, while the Z1,2 concentration increases during post-irradiation thermal treatment the opposite holds for the EH6,7 level especially in silicon rich samples. On the basis of these results, the influence of carbon and nitrogen on the formation of the Z1,2 complex is reconfirmed and a possible identity of the EH6,7 defect is discussed.