Out-of-Hospital cardiac arrest & SmartphonE RespOndErS trial (HEROES Trial): Methodology and study protocol of a pre-post-design trial of the effect of implementing a smartphon... oleh Michael P. Müller, Julian Ganter, Hans-Jörg Busch, Georg Trummer, Jörg Sahlmann, Florian Brettner, Maria Reden, Daniel Elschenbroich, Michael Preusch, Jonas Rusnak, Stephan Katzenschlager, Dirk Nauheimer, Robert Wunderlich, Jan-Steffen Pooth