Received: 5 March 2019
Accepted: 7 November 2019
First Online: 15 November 2019
Ethics approval and consent to participate
: Because of the strictly retrospective design of our study, approval by a local ethics committee and written informed consent from the participants were not required, in accordance with German law (paragraph 15, sentence 1, North Rhine Medical Association’s professional code of conduct from 14 November 1998 as amended on 19 November 2011, and paragraph 6, sentence 1, Health Data Protection Act of North Rhine-Westphalia).
: Not applicable.
: The authors declare that they have no competing interests.