Received: 3 July 2018
Accepted: 3 October 2018
First Online: 30 October 2018
Ethics approval and consent to participate
: This study was approved by the Institutional Review Board of SNUBH (B-1704/390–104), which waived the need for informed consent on account of the retrospective study design.
: Not applicable.
: The authors declare that they have no competing interests.
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